iii
Specially Dedicated To my Beloved Mother
To my Husband, Ervan Latuhari
To my parents in law,
To my Family, Brothers and Sisters
iv
ACKNOWLEDGEMENT
First of all, I thank Almighty Allah, The Creator, for Mercy and Guidance in
my whole life and giving me the ability to complete this research.
I would like to express my sincere appreciation and deepest gratitude to my
supervisor, Assoc. Prof. Dr. Salasiah Endud, Dr. Hadi Nur and Assoc. Prof. Dr.
Zainab Ramli for their supervision, guidance, encouragement, advice, critics,
motivation, and patience. Without their support and assistance, this thesis would not
have been the same as presented here. It has been truly memorable and educative
being a researcher under their supervision. I wish to express special appreciation to
Prof. Dr. Halimaton Hamdan, Didik Prasetyoko, M.Sc. and Zeolite and Porous
Material Group (ZPMG) members for their help support and valuable hints.
I am also indebted to Ministry of Science, Technology and Innovation (MOSTI) for
its support in providing the research grant for the IRPA funding 09-02-06-0057SR0005/09-04. My study would not have been possible without this funding. I must
give my special thanks to Ibnu Sina Institute for Fundamental Science Studies,
Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia and
also my research friends, thank you for your help and support.
My sincere appreciation also extends to all of my dearest family in
www.S36chantique.com and all my sisters in H21 who have given me a beautiful
friendship. I thank all of them, who are too numerous to mention each of them
individually. And last, I would like to give greatest thank to my beloved mother,
Andi Djuaeda, my parents in law, my dearest sisters and brothers, and all of my
lovely big family, for their support, encouragement, care and love. And especially
grateful to someone who is very patience, love, and supportive to me, my husband
Ervan Latuhari, thank you so much.
v
ABSTRACT
Mesoporous molecular sieve Al-MCM-41 with Si/Al=20 and polymethacrylic
acid (PMAA) were used as supports for the immobilization of bulky iron(III)5,10,15,20-tetra-(4-pyridyl) porphyrin (Fe-TPyP). Metalloporphyrin of Fe(III) was
encapsulated inside the mesopores of the ordered structure of Al-MCM-41 by
sequential synthesis of Fe-TPyP via treatment of FeCl3 with 5,10,15,20-tetra-(4pyridyl) porphyrin (TPyP), followed by encapsulation of Fe-TPyP. Fe-TPyP
complexes were also successfully encapsulated into PMAA by polymerizing
methacrylic acid (MAA) with a cross-linker around the Fe-TPyP complexes. The
materials obtained were characterized by X-ray Diffraction (XRD), Fourier
Transform Infrared (FTIR), Ultraviolet Visible Diffuse Reflectance (UV-Vis DR),
Electron Spin Resonance (ESR), Luminescence and 13C CP/MAS NMR
spectroscopies, Thermogravimetric Analysis (TGA) and elemental analysis. The
powder XRD data confirmed that the ordered structure of mesoporous Al-MCM-41
remained intact after encapsulation process. Characterization of Fe-TPyP composite
with Al-MCM-41 and PMAA using FTIR, UV-Vis DR and ESR confirmed that the
structure of Fe-TPyP in inorganic and polymer supports is similar with bare
Fe-TPyP. The specific interaction of Fe-TPyP in Al-MCM-41 and/or PMAA was
studied by ESR, 13C CP/MAS NMR and Luminescence spectroscopies. The ESR
spectra of Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA composites showed that there
is a shift towards a higher g-value confirming the interaction between Fe-TPyP and
supports is occurred. By quenching of the luminescence spectra of Fe-TPyP/PMAA
with various concentration of Fe-TPyP, it is evidenced that there is some interaction
between Fe-TPyP and PMAA. Further evidence of interaction was corroborated by
13
C CP/MAS NMR spectra with show that the peak of carboxyl of PMAA is shifted
to higher magnetic field. Single-point BET surface area analysis was used to
determine specific surface area of the composites. It is revealed that the surface area
of Fe-TPyP/Al-MCM-41 composites is decreased with an increase in Fe-TPyP,
suggesting the encapsulation of the complex in the pores of Al-MCM-41 has been
achieved. With mesoporous molecular sieve (Al-MCM-41) and the polymer
(PMAA) as supports, the immobilized iron-porphyrin system has demonstrated
excellent activity for the single-step synthesis of phenol from benzene under mild
reaction conditions. The effect of reaction time, solvent, amount of Fe-TPyP loading,
temperature and the performance of the recovered catalysts have been studied. The
immobilized iron-porphyrin in PMAA (Fe-TPyP/PMAA) gives a higher activity
compared to Fe-TPyP supported on Al-MCM-41 (Fe-TPyP/Al-MCM-41). However,
the product selectivity of Fe-TPyP/PMAA is not as good as that of Fe-TPyP/
Al-MCM-41. Thus, it is reasonable to assume that the hydrophobic nature of
Fe-TPyP/PMAA would account for the high activity, while the rigid, ordered
structure of Fe-TPyP/Al-MCM-41 would contribute towards the high selectivity in
the single-step synthesis of phenol from benzene in the present study.
vi
ABSTRAK
Penapis molekul mesoliang Al-MCM-41 dengan nisbah Si/Al = 20 dan asid
polimetakrilik (PMAA) telah digunakan sebagai penyokong untuk pemegunan
kompleks ferum(III)-5, 10, 15, 20-tetra-(4-piridil) porfirin (Fe-TyP). Ferum-porfirin
telah dikapsulkan di dalam mesoliang Al-MCM-41 secara sintesis berturutan
Fe-TPyP melalui tindak balas FeCl3 dengan 5, 10, 15, 20-tetra-(4-piridil) porfirin
(TPyP), dan diikuti pengkapsulan Fe-TPyP. Kompleks Fe-TPyP juga telah berjaya
dikapsulkan ke dalam PMAA melalui proses pempolimeran asid metakrilik (MAA)
dengan perangkai silang di sekitar kompleks. Sampel yang terhasil dicirikan dengan
menggunakan kaedah XRD, spektroskopi FTIR, UV-Vis DR, ESR, pendarcahaya
dan 13C CP/MAS NMR, TGA dan analisis unsur. Data XRD menunjukkan bahawa
struktur mesoliang Al-MCM-41 yang teratur masih wujud setelah proses
pengkapsulan. Pencirian komposit Fe-TPyP dengan Al-MCM-41 dan PMAA dengan
kaedah FTIR, UV-Vis DR dan ESR, menunjukkan bahawa struktur Fe-TPyP di
dalam penyokong tak organik dan polimer adalah serupa dengan kompleks asal
Fe-TPyP. Interaksi spesifik Fe-TPyP dalam Al-MCM-41 dan/atau PMAA dikaji
dengan kaedah spektroskopi ESR, pendarcahaya dan 13C CP/MAS NMR. Spektrum
ESR bagi komposit Fe-TPyP/Al-MCM-41 dan Fe-TPyP/PMAA memperlihatkan
anjakan ke arah nilai-g yang lebih tinggi, menunjukkan adanya interaksi antara
Fe-TPyP dan penyokong. Pelindapan spektrum pendarcahaya bagi Fe-TPyP/PMAA
dengan pelbagai kepekatan Fe-TPyP membuktikan terjadinya interaksi antara
Fe-TPyP dan PMAA. Bukti interaksi tersebut juga turut disokong dengan spektrum
13
C CP/MAS NMR yang menunjukkan anjakan puncak karboksil bagi PMAA ke
medan magnet yang lebih tinggi. Analisis luas permukaan BET titik tunggal telah
digunakan untuk penentuan luas permukaan spesifik komposit. Luas permukaan
komposit Fe-TPyP/Al-MCM-41 didapati menurun dengan pertambahan kandungan
Fe-TPyP, menunjukkan bahawa Fe-TPyP telah terkapsulkan di dalam liang
Al-MCM-41. Sampel penapis molekul mesoliang (Al-MCM-41) dan polimer
(PMAA) sebagai penyokong, sistem ferum-porfirin yang dikapsulkan dalam
penyokong telah digunakan untuk sintesis langkah tunggal fenol dari benzena pada
keadaan tindak balas yang sederhana. Pengaruh masa tindak balas, pelarut, jumlah
kandungan Fe-TPyP, suhu dan penjanaan semula mangkin bagi tindak balas tersebut
juga telah dikaji. Ferum-porfirin yang terkapsulkan di dalam PMAA (Fe-TPyP/
PMAA) menunjukkan keaktifan yang lebih tinggi berbanding Fe-TPyP/Al-MCM-41.
Manakala kepilihan hasil tindak balas menggunakan mangkin Fe-TPyP/PMAA
adalah tidak sebaik dengan Fe-TPyP/Al-MCM-41. Maka, adalah dianggapkan
bahawa sifat kehidrofobik Fe-TPyP/PMAA mungkin berperanan meningkatkan
keaktifan mangkin, manakala struktur tegar dan teratur Fe-TPyP/Al-MCM-41 pula
menghasilkan kepilihan yang tinggi dalam sintesis langkah tunggal fenol dari
benzena dalam kajian ini.
vii
TABLE OF CONTENTS
CHAPTER
TITLE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF SCHEMES
x
LIST OF TABLES
xi
LIST OF FIGURES
xii
ABBREVIATIONS
xv
LIST OF APPENDICES
1
2
PAGE
xvii
INTRODUCTION
1.1
Research Background and Problem Statement
1
1.2
Research Objectives
8
1.3
Scope of Study
9
1.4
Outline of Research
10
1.5
Outline of Thesis
11
LITERATURE REVIEW
2.1
Introduce to Metalloporphyrins Complexes
12
2.2
Heterogenization of Metalloporphyrins
14
viii
2.2.1
2.2.2
16
Metalloporphyrins Supported on Polymer
Matrix
21
2.3
Oxidation of Benzene to Phenol
23
2.4
Characterization Techniques
25
2.4.1
X-ray Powder Diffraction (XRD)
26
2.4.2
Fourier Transform Infrared Spectroscopy
(FTIR)
27
UV-Vis Diffuse Reflectance Spectroscopy
(UV-Vis DR)
29
2.4.4
Electron Spin Resonance (ESR)
30
2.4.5
Atomic Absorption Spectroscopy (AAS)
32
2.4.6
Single-Point BET Surface Area Analysis
33
2.4.7
Thermogravimetry Analysis (TGA)
34
2.4.8
Scanning Electron Microscopy (SEM)
35
2.4.9
Luminescence Spectroscopy
36
2.4.3
2.4.10
3
Metalloporphyrins Supported on Molecular
Sieves
13
C CP Magic-Angle-Spinning NMR
Spectroscopy (13C CP/MAS NMR)
37
ENCAPSULATION OF IRON(III)-PORPHYRIN
WITHIN ORDERED MESOPOROUS Al-MCM-41
3.1
Direct Synthesis of Mesoporous Molecular Sieve AlMCM-41
39
Preparation of Iron(III)-Tetra (4-Pyridyl) Porphyrin
(Fe-TPyP)
40
3.3
Preparation of Fe-TPyP/Al-MCM-41
40
3.4
Results and Discussion
42
3.4.1
42
3.2
Characterization of Al-MCM-41
3.4.2 Characterization of Iron(III)-Tetra (4-Pyridyl)
Porphyrin
47
3.4.3 Characterization of Fe-TPyP/Al-MCM-41
50
ix
4
IMMOBILIZATION OF IRON(III)-PORPHYRIN
IN POLYMETHACRYLIC ACID
4.1
Polymethacrylic acid as Organic Support
64
4.2
Synthesis of Polymethacrylic acid (PMAA)
65
4.3
Synthesis of Fe-TPyP/PMAA
65
4.4
Results and Discussion
66
4.4.1
Characterization
(PMAA)
of
Polymethacrylic
acid
4.4.2 Characterization of Fe-TPyP/PMAA
5
70
SINGLE-STEP SYNTHESIS OF PHENOL FROM
BENZENE OVER Fe-TPyP/Al-MCM-41 AND Fe-TPyP/
PMAA CATALYSTS
5.1
Reaction Mechanism of Benzene Oxidation to Phenol
82
5.2
The Single-Step Synthesis of Phenol from Benzene
83
5.3
Analysis of Reaction Products
85
5.3.1
Gas Chromatography (GC)
85
5.3.2
Gas Chromatography – Mass Spectrometry
Analysis (GC-MS)
86
High Performance Liquid Chromatography
(HPLC)
87
5.3.3
5.4
6
66
Results and Discussion
89
5.4.1
Catalytic Activity
89
5.4.2
The Selectivity of Products
91
5.4.3
Regenerability of Catalysts
92
5.4.4
Optimization of Reaction Condition
94
CONCLUSION AND RECOMMENDATION
98
REFERENCES
101
APPENDICES
1090
x
LIST OF SCHEMES
SCHEME NO
1.1
5.1
5.2
TITLE
Basic features of the cytochrome P-450 oxidation
mechanism
PAGE
2
The probable products of benzene oxidation (phenol,
hydroquinone, catechol, resorcinol and benzoquinone)
83
Proposed reaction path for the oxidation of benzene
84
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
3.1
XRD data and lattice parameter of the Al-MCM-41 samples
46
3.2
Assignment of FTIR bands of TPyP and Fe-TPyP complexes
49
3.3
XRD data of iron-containing Al-MCM-41 catalysts
55
3.4
Iron content (%Fe) of Fe-TPyP/Al-MCM-41 with different
amount of Fe-TPyP loading
60
Surface properties of Al-MCM-41-supported Fe-TPyP with
different amount of Fe-TPyP loading
60
Assignment of 13C CP/MAS NMR spectrum of PMAA
69
3.5
4.1
4.2
13
Assignment of chemical shift of C CP/MAS NMR spectra
of as-synthesized PMAA and Fe-TPyP/PMAA with various
of amount of Fe-TPyP loading
79
Iron content (%Fe) of Fe-TPyP/PMAA with different amount
of Fe-TPyP loading determined by AAS
79
Surface properties of PMAA-supported Fe-TPyP with
different amount of Fe-TPyP loading
81
5.1
GC-FID oven-programmed setup for identifying phenol
86
5.2
Catalytic activity of single-step synthesis of phenol from
benzene
89
The catalytic activity of Fe-TPyP supported in Al-MCM-41
and polymethacrylic acid (PMAA) during the recycling in
single-step synthesis of phenol from benzene
93
4.3
4.4
5.3
xii
LIST OF FIGURES
FIGURE NO
1.1.
TITLE
PAGE
Commercial routes to synthesize phenol from benzene
(with cumene as an intermediate)
6
1.2.
Oxidation reaction of benzene to phenol with dioxygen
8
2.1.
Structure of iron(III) tetra-(4-pyridyl)-porphyrin (Fe-TPyP)
14
2.2.
Structure of zeolite NaX (I) and iron(III) porphyrins (FeP)
17
2.3.
M41S family of mesoporous materials: (a) hexagonal
MCM-41; (b) cubic MCM-48; (c) lamellar MCM-50
19
Horväth-Kawazoe pore size distribution for MCM-41,
zeolite Y and amorphous silica
20
Schematic of the structure of the mesoporous material
MCM-41 with cylindrical mesopores packed in a
hexagonal array and amorphous siliceous pore walls
20
Polymer immobilized rhodium catalyst, PRH. PRH was
prepared from the copolymerization of
[(idppe)Rh(nbd)]BF4 (2 mol%) into an ethylene
dimethacrylate-based polymer (98 %)
23
One-step benzene to phenol conversion using N2O in the
gas phase
25
2.8
Bragg reflection diagram
26
2.9
Optical layout of the Michelson interferometer (S = IR
source, D = detector)
28
2.10
The IUPAC classification of adsorption isotherms
33
3.1
Reaction of TPyP with FeCl3 in ethanol in the synthesis of
iron-porphyrin complexes
41
Theoretical encapsulation of Fe-TPyP within ordered
mesoporous Al-MCM-41
42
FTIR spectra of (a) as-synthesized and (b) calcined
samples of Al-MCM-41
43
2.4.
2.5.
2.6.
2.7.
3.2
3.3
xiii
3.4
3.5
XRD patterns of the
Al-MCM-41 samples
as-synthesized
and
calcined
45
TGA thermograms of (a) as-synthesized and (b) calcined
samples of Al-MCM-41
46
3.6
FTIR spectra of (a) TPyP and (b) Fe-TPyP complexes
48
3.7
UV-Vis DR spectra of (a) TPyP and (b) Fe-TPyP
50
3.8
FTIR spectra of (a) Fe-TPyP complexes, (b) Al-MCM-41
and (c) Fe-TPyP/Al-MCM-41
51
FTIR spectra of Fe-TPyP/Al-MCM-41 with various of
Fe-TPyP loadings
53
XRD patterns of Al-MCM-41 and Fe-TPyP/Al-MCM-41
with various of Fe-TPyP loadings
54
UV-Vis DR spectra of (a) Fe-TPyP and (b) Fe-TPyP/
Al-MCM-41
56
UV-Vis DR spectra of Fe-TPyP/Al-MCM-41 with various
of amount of Fe-TPyP loading
57
3.13
ESR spectra of (a) Fe-TPyP and (b) Fe-TPyP/Al-MCM-41
58
3.14
ESR spectra of Fe-TPyP and Fe-TPyP/Al-MCM-41 with
various amount of Fe-TPyP loading
59
TGA thermograms of (a) calcined Al-MCM-41,
(b) Fe-TPyP/Al-MCM-41 and (c) Fe-TPyP complexes
61
Scanning electron micrographs of (a) Al-MCM-41 and
(b) Fe-TPyP/Al-MCM-41
62
Proposed mechanism of Fe-TPyP complex-Al-MCM-41
supports interaction
63
4.1
Structure of polymethacrylic acid (PMAA)
65
4.2
Schematic representation of the procedure of synthesis of
composite Fe-porphyrin-polymethacrylic acid. Methacrylic
acid (MAA) monomers assemble with the metalloporphyrin, followed by cross-linking polymerization
66
FTIR spectrum of as-synthesized polymethacrylic acid
(PMAA)
67
TGA thermograms of as-synthesized polymethacrylic acid
(PMAA)
68
4.5
The luminescence excitation and emission spectra of assynthesized polymethacrylic acid (PMAA) (Ȝex = 333 nm ,
Ȝem = 574 nm)
68
4.6
13
3.9
3.10
3.11
3.12
3.15
3.16
3.17
4.3
4.4
4.7
C CP/MAS NMR spectrum of as-synthesized
polymethacrylic acid (PMAA)
69
FTIR spectra of (a) Fe-TPyP complexes, (b) as-synthesized
PMAA and (c) Fe-TPyP/PMAA
71
xiv
4.8
UV-Vis DR spectra of (a) Fe-TPyP and (b) Fe-TPyP/
PMAA
72
UV-Vis DR spectra of Fe-TPyP/PMAA with various of
amount of Fe-TPyP loading
73
ESR spectra of Fe-TPyP and Fe-TPyP/PMAA (containing
50 and 100 µmol Fe-TPyP)
74
The luminescence emission spectra of (a) as-synthesized
PMAA, (b) Fe-TPyP/PMAA and (c) Fe-TPyP
Ȝex = 333 nm)
75
The luminescence emission spectra of as-synthesized
PMAA and Fe-TPyP/PMAA with different of amount of
Fe-TPyP loading (Ȝex = 333 nm)
76
4.13
The Stern-Volmer kinetics: the dependence of the ratio of
the luminescence intensities (I0/I) on the Fe-TPyP
concentration
77
4.14
13
4.9
4.10
4.11
4.12
C CP/MAS spectra of Fe-TPyP/PMAA with various of
amount of Fe-TPyP loading (a) 100 ȝmol, (b) 50 ȝmol,
(c) 25 ȝmol, (d) 5 ȝmol and (e) as-synthesized PMAA
78
TGA thermograms of (a) Fe-TPyP complexes,
(b) Fe-TPyP/PMAA and (c) as-synthesized
polymethacrylic acid (PMAA)
80
5.1
Block diagram of a gas chromatograph
86
5.2
Effect of the difference catalyst on the phenol yield for 20
hours reaction
90
The product selectivity of single-step synthesis of phenol in
aqueous hydrogen peroxide using Fe-TPyP/Al-MCM-41
and Fe-TPyP/PMAA catalysts
91
The percentage conversion of benzene to phenol in aqueous
hydrogen peroxide using Fe-TPyP/Al-MCM-41 and
Fe-TPyP/PMAA
92
Effect of reaction time on the phenol yield in the singlestep synthesis of phenol from benzene over Fe-TPyP/
Al-MCM-41 and Fe-TPyP/PMAA catalysts
95
Effect of different solvent on phenol yield using Fe-TPyP/
Al-MCM-41 and Fe-TPyP/PMAA as catalysts at 70 °C
95
Effect of amount of Fe-TPyP loading on the phenol yield in
free-solvent at 70 °C for 20 hours reaction time over
Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA catalysts
96
Effect of reaction temperature on phenol yield in freesolvent for 20 hours reaction time over Fe-TPyP/
Al-MCM-41 and Fe-TPyP/PMAA catalysts
97
4.15
5.3
5.4
5.5
5.6
5.7
5.8
xv
ABBREVIATIONS
λ
wavelength
2θ
Bragg angle
AAS
Atomic Absorption Spectroscopy
Al-MCM-41
Aluminium Mobil Crystalline Materials-41
CuKα
X-ray diffraction from copper KĮ energy levels
CP/MAS NMR
Cross-Polarization Magic-Angle-Spinning Nuclear
magnetic Resonance
UV-Vis DR
Ultraviolet Visible Diffuse Reflectance
Fe-TPyP
iron(III)-tetra-(4-pyridyl)porphyrin
FTIR
Fourier Transform Infrared
GC
Gas Chromatography
GC-MS
Gas Chromatography – Mass Spectrometry
h
hour
HPLC
High Performance Liquid Chromatography
IR
Infrared
KBr
Potassium bromide
MAS NMR
Magic-angle-spinning nuclear magnetic resonance
MCM-41
Mobil Crystalline Materials-41
Fe-TPyP/Al-MCM-41
iron(III)-porphyrin supported on Al-MCM-41
OH
hydroxyl
PMAA
Polymethacrylic acid
EGDMA
ethylene glycol dimethacrylate
AIBN
2.2’-azobis (2-methyl) propionitrile
Fe-TPyP/PMAA
iron(III)-porphyrin supported on polymethacrylic acid
SEM
Scanning Electron Microscopy
Si/Al
silicon-to-aluminium ratio
xvi
TGA
Thermogravimetric Analysis
TO4
Tetrahedral unit where T = Al or Si
TPyP
Tetra-(4-pyridyl)-porphyrin
TS-1
Titanium silicalite
XRD
X-ray Diffraction technique
ESR
Electron Spin Resonance
TON
Turnover Number
xvii
LIST OF APPENDICES
APPENDIX
TITLE
A
Ultraviolet-Visible Diffuse Reflectance Spectroscopy
(UV-Vis DR)
109
B
Luminescence Spectroscopy (LS)
110
C
Scanning Electron Microscopy (SEM)
111
D
Gas Chromatography (GC)
113
E
Gas Chromatography-Mass Spectrometry (GC-MS)
118
F
High Performance Liquid Chromatography (HPLC)
124
G
Reaction Path for the Oxidation of Benzene to
Phenol
126
List of Publications
128
H
PAGE
CHAPTER 1
INTRODUCTION
1.1
Research Background and Problem Statement
Selective catalytic oxidation of hydrocarbons under mild conditions is of
academic interest and industrial importance [1]. In synthetic organic chemistry,
oxidation represents one of the most important methods for substrate
functionalization and functional group transformation. In the chemical industry,
oxygenated products of petroleum namely, alcohols, aldehydes or acids, are
important feedstocks for various industrial processes.
Traditionally, oxidation of hydrocarbons are performed with stoichiometric
amounts of inorganic oxidants such chromium chloride and potassium permanganate
[2]. The use of these oxidants for oxidation reaction leads to a big environmental
problem because of the generation of numerous amounts of by-products.
In recent years, as a result of increasing environmental constraints, “clean”
oxidants such as dioxygen (or air), hydrogen peroxide, and alkyl hydroperoxides,
which are inexpensive, is becoming more important both in industry and academia,
and chemical processes based on cleaner technologies are expected to increase
significantly in the next few years.
2
In biological systems, nature has its unique way for doing selective O2
oxidation, which is accomplished by certain enzymatic systems. Some enzymes of
the mono- and dioxygenase types incorporate one or both oxygen atoms of O2
respectively into a substrate.
A well-known monooxygenase, iron porphyrin-based cytochrome P-450, has
been the subject of intensive study [3] largely because of their ability to catalyze a
wide variety of oxidation transformations, such as alkenes epoxidation and alkanes
hydroxylation with molecular oxygen. The key steps in the catalytic cycle is
reductive activation of O2, whereby one oxygen atom is reduced to H2O and the other
oxygen atom becomes available to form a high-valent iron oxo species for the
oxidation process (see Scheme 1.1) [4]. In the last two decades, therefore, increasing
attention in catalytic oxidation has been focused on the reactivity and oxidation
properties of biomimetic systems based on Fe(II), Ru(II) and Mn(II)[5-7].
SO
Fe
III
e
S
II
Fe
FeV O
O2
II
H2O
Fe (O2)
FeIII O22-
e
2H+
Scheme 1.1
Basic features of the cytochrome P-450 oxidation mechanism [4]
3
Synthetic metalloporphyrins are widely used as homogeneous catalysts for
hydrocarbon oxidation,
as well as model for cytochrome P-450 [8-9].
Metalloporphyrin complexes of iron [10], manganese [11] and ruthenium are known
to be active catalysts for alkenes epoxidation. There are, however, several
disadvantages in using metalloporphyrins as catalysts in homogeneous oxidation
processes. The difficulty in separating the catalysts from the product substantially
increases the cost of using homogeneous catalysis in commercial processes.
Heterogeneous catalysts, on the contrary, can be easily separated from the
reaction products simply by filtration. Yet most heterogeneous catalysts are less
selective in complex reactions. Therefore, it is highly desirable to develop materials
based on metalloporphyrin, which possess both the high selectivity of homogeneous
catalysts and the convenience of heterogeneous catalysts. One approach to achieve
this goal is to immobilize homogeneous catalysts on porous solid supports, which
simultaneously has the advantages of tuning the liquid phase oxidation from
homogeneous into heterogeneous.
Microporous materials with regular arrays of internal channels and uniform
pores such as zeolite [12] have been extensively studied as inorganic support.
Immobilization of metalloporphyrin catalysts on microporous zeolite appears to be a
good way to render these materials active for organic substrate oxidation.
Zeolites have large internal surfaces and specific sites available for active
metal substitution thus allowing the preparation of materials for selective processes.
Furthermore, the uniform pore sizes provide both size- and shape-selectivity towards
the reactant and product molecules. Based on isomorphous substitution approach a
number of materials of potential industrial usage have been developed. A typical
example is TS-1, a titanium modified silicalite that catalyses olefin epoxidation,
alcohol oxidation and phenol hydroxylation with 30% hydrogen peroxide [13]. In
addition, metalloporphyrin complex such as cis-Mn(bypy)3 [14] encapsulated in
zeolite Y have been reported to be active catalysts towards cyclohexene oxidation.
4
Supporting metalloporphyrins on zeolite also provides a physical separation
of active sites, thus minimizing catalyst self-destruction and dimerization of
unhindered metalloporphyrins [15]. Although this approach has been demonstrated
to be very successful, the main problem is the pore sizes of zeolites are very small
(<13 Å) which limit their applications to reactions in which large molecules are
involved [16].
In 1992, Beck et al. [17] reported the preparation and characterization of a
new family of crystalline mesoporous molecular sieves, which are designated as
M41S. MCM-41 is a member of this family associated with unique pores (20-100 Å)
and large well-defined internal surface areas (>1000 m2 g-1). Due to the large pores
of these mesoporous molecular sieves, high molecular mass organic molecules can
easily gain access into the pores.
Transition metal complexes and organometallic compounds can be
immobilized onto the mesoporous MCM-41 supports by physical adsorption or
covalent linkage. Titanocene dichloride was anchored to MCM-41 by Maschmeyer
et al. [18]. Copper-salen and iron-salen complexes encapsulated in the channels of
Al-MCM-41 have been reported to be an active catalyst towards polymerization of
bisphenol-A at room temperature using hydrogen peroxide as oxidant and dioxane as
solvent [19]. More recently, much effort was focused on the immobilization of
metalloporphyrins onto the silica MCM-41 surface.
Che and co-workers [20] have immobilized a ruthenium porphyrin on
modified MCM-41. It was reported that the derived catalyst gives higher turnover
numbers (TON) in the epoxidation of olefins than the free ruthenium porphyrin. It is
interesting to note that in the oxidation of cis-stilbene with the modified MCM-41
material, the major product was trans-stibene oxide. In contrast, oxidation of cisstilbene catalyzed by free ruthenium porphyrin gave a 1:1 mixture of cis- and transstilbene oxides. The high selectivity to give trans-stilbene oxide was attributed to the
steric constraint imposed by the uniform channels of the MCM-41 support. This
example demonstrated the potential of mesoporous MCM-41 materials as size and
shape selective catalysts.
5
Stimulated by these works, we are interested in modifying the MCM-41
materials with metalloporphyrin as catalysts for selective oxidation reactions.
MCM-41 can serve as a support for the metalloporphyrin species by providing a
large surface area and uniform surface for catalytic reaction. The larger pore
dimensions would allow processing of bulky chemicals of interest.
In this research, iron porphyrin has been immobilized within ordered
mesoporous Al-MCM-41.
It is well known that iron porphyrin complexes is
effective catalyst for the conversion of olefins into trans-diols or trans-diol monoethers by using H2O2 [21]. In order to tune the activity of the supported catalysts the
knowledge on the microenvironment of the immobilized complexes is essential.
However, there are few reports on correlation between the structure of the
immobilized catalysts and the catalytic activities. It is anticipated that immobilization
of the metalloporphyrins in inorganic or organic support will stabilize and/or modify
the catalytic performance by influencing the chemoselectivity, regioselectivity and
shape selectivity of the reaction.
Supported catalysts are also often plagued by leaching of the metal into
solution. Our approach to this problem is to radically change the nature of the
support. The even distribution of large, regular pores and extremely high surface area
that characterizes mesoporous molecular sieve MCM-41 makes them ideal supports.
This support has the added benefit that the silica structure has stability to chemical
reagents. Also, easy separation of the products from the separation medium, along
with the recovery and reuse of the expensive catalyst provide an attractive advantage
over homogeneous catalysts.
The key feature of the MCM-41, which separates it from currently used
zeolite support, is its extreme porosity. However, the MCM-41, an inorganic
material, is hydrophilic and rigid. In this research, we also propose a procedure to
immobilize iron porphyrin on the polymer support, namely polymethacrylic acid
(PMAA). One expects that the flexibility and hydrophobicity of the polymer as
support give certain advantages in oxidation of organic compounds. The production
of porous polymers containing large aromatic moieties or transition metal complexes
such as the iron porphyrin complexes is considered to be useful, since they are in
6
high demand for a variety of applications ranging from catalysis, chromatography,
diagnostics and sensors [1]. To the best of our knowledge, iron porphyrin complexes
supported on PMAA has not yet been reported.
Phenol is produced globally on the scale of 17 billion pounds/year [22] due to
demand for bisphenol A (polycarbonate resins), phenolic resins, coprolactam (nylon
6.1), xylenols, aniline, alkylphenols and others. It is used in the manufacture of
plywood, construction, automotive and appliance industry. It is also used as a raw
material in the production of nylon and epoxy resins, disinfectant and slime-killing
agent.
Phenol has been mainly manufactured using the cumene method by which the
selectivity for the phenol is high. However, this cumene process consists of three
steps and produces acetone as a byproduct (Figure 1.1) [23]. The efficiency of the
three-step cumene process strongly depends on the price of the by-product acetone,
which is considerably varying.
Phosporic acid
+
+
O2
AlCl3
Benzene
O
Propene
Cumene
Air
H
O
OH
O
Acid
+
H2SO4
Cumene
hydroperoxide
Figure 1.1
Phenol
Acetone
Commercial routes to synthesize phenol from benzene (with cumene
as an intermediate) [23]
7
The cumene method has several significant shortcomings: it is a multistage
synthesis; the intermediate cumene hydroperoxide is explosive; there are ecological
problems and the production rate of the co-product acetone exceeds market demand.
Therefore, both industry and academia are intensively searching for new routes to
phenol based on direct benzene oxidation. The single-step synthesis of phenol from
benzene would be an alternative.
The single-step production of phenol by direct insertion of oxygen into the
benzene ring is an attractive and challenging method, not only from a practical point
of view but also from a synthetic chemical point of view, because the direct
oxygenation of the energetically stable benzene to produce phenol has been one of
the most difficult oxidation reactions [24].
The gas-phase oxidation of benzene to phenol by nitrous oxide has been
widely studied over Fe-ZSM-5 [25]. In the presence of Fe-ZSM-5, the selectivity of
benzene and N2O for phenol exceeded 98 and 95%, respectively, but the conversion
of benzene to phenol is very low. The oxidation of benzene to phenol over
H6PMo 9V3O40 and palladium acetate in VPI-5 and MCM-41 has been reported in the
presence of molecular oxygen [26]. Over H6PMo9V3O40, after 4 hours at 130 oC the
benzene conversion is 15% and the selectivity for phenol is above 70%.
Phenol synthesis by liquid-phase oxidation of benzene with hydrogen
peroxide has been also studied using iron-heteropoly acid [27]. Furthermore,
Miyahara et al. has studied the liquid-phase oxidation of benzene to phenol catalyzed
by Cu catalysts supported on zeolites [28], and MCM-41 [29], and also supported
CuO catalysts (CuO-Al2O3) [24]. In the presence CuO-Al2O3, the phenol yield is
very low (< 1%) and the leaching of Cu is less than 10%.
An attractive alternative route is the direct oxidation of benzene to phenol
using molecular oxygen and a suitable catalyst. A one-step process such as this
would require less energy and generate zero waste, while producing only phenol.
This reaction model of hydroxylation of benzene with oxygen is presented in Figure
1.2.
8
OH
O2 / H2O2
Catalyst
Figure 1.2 Oxidations reaction of benzene to phenol with dioxygen
Recently, the best catalyst for benzene to phenol oxidation by nitrous oxide is
Fe-ZSM-5 zeolite, which provides nearly 100% benzene selectivity, but low
conversion of benzene [25]. The remarkable catalytic performance of this zeolite was
show to be related to the presence of iron and upon high temperature treatment. In
these systems, the reaction only occurs in the gas phase (ca. 300º) and there is no
report on single-step liquid phase oxidation of benzene to phenol in the literature. For
these reasons, in this research, we will study the single-step liquid phase oxidation of
benzene to phenol using iron(III)-porphyrin supported on Al-MCM-41 and
polymethacrylic acid (PMAA).
1.2
Research Objectives
The main objectives of the research are:
i.
To synthesize Al-MCM-41 and polymethacrylic acid (PMAA).
ii.
To
synthesize
complexes
iron(III)
supported
tetra-(4-pyridyl)-porphyrin
on
mesoporous
(Fe-TPyP)
Al-MCM-41
and
polymethacrylic acid (PMAA) matrix.
iii.
To
investigate
the
physicochemical
properties
of
Fe-TPyP
encapsulated in Al-MCM-41 and Fe-TPyP supported on polymer
matrix.
iv.
To compare the performance of the hybrid catalysts of Fe-TPyP
supported on mesoporous Al-MCM-41 and polymethacrylic acid
(PMAA) in the single-step synthesis of phenol from benzene.
9
1.3
Scope of Study
The scope of this research is to synthesize iron(III)-porphyrin encapsulated
Al-MCM-41 and iron(III)-porphyrin supported on polymethacrylic acid (PMAA), to
characterize these catalyst by XRD, FTIR, UV-Vis DR, ESR, Luminescence, and 13C
CP/MAS NMR spectroscopies along with Single-point BET surface area analysis,
AAS, TGA and SEM, to test the performance of these catalysts for the liquid phase
single-step oxidation of benzene to phenol and finally, to analyze the reaction
products using GC, GC-MS and HPLC techniques.
10
1.4
Outline of Research
•
Synthesis of iron(III) tetra-(4-pyridyl)-porphyrin
(Fe-TPyP)
Characterization of catalysts using FTIR and
UV-Vis DR spectroscopies.
No
•
Yes
Synthesis of iron(III)-porphyrin supported on mesoporous Al-MCM-41
(Fe-TPyP/Al-MCM-41)
•
Synthesis of iron(III)-porphyrin supported on polymethacrylic acid
(Fe-TPyP/PMAA)
Characterization of catalysts by FTIR, XRD, UV-Vis DR, ESR, Luminescence
and 13C CP/MAS NMR spectroscopies along with AAS Single-point BET
Single-step synthesis of phenol from benzene
Analysis of reaction product by GC,
GC-MS, HPLC
11
1.5
Outline of Thesis
This thesis focuses on the development of hybrid catalyst systems with the
main aim at the preparation, characterization and catalytic application of iron(III)porphyrin (Fe-TPyP) supported on mesoporous molecular sieve Al-MCM-41 and
polymethacrylic acid (PMAA). This thesis is also organized into six chapters.
Chapter 1 describes the research background and problem statement, research
objectives, scope of the research, outline of research and outline of the thesis.
Chapter 2 presents some literature review on the chemistry of metalloporphyrin, mesoporous molecular sieve MCM-41, the polymer support, and the
liquid-phase oxidation of benzene to phenol.
Chapter 3 demonstrates that iron(III) tetra-(4-pyridyl)-porphyrin (Fe-TPyP)
may be encapsulated into the pores and channels of the mesoporous material
Al-MCM-41 by impregnation method, while Chapter 4 presents the preparation of
iron-porphyrin
supported
into
polymethacrylic
acid
(PMAA)
by
direct
polymerization of iron(III) tetra-(4-pyridyl)-porphyrin (Fe-TPyP) with the monomer,
methacrylic acid (MAA).
Chapter 5 discusses the catalytic activity of these materials in the single-step
synthesis of phenol from benzene. Finally, Chapter 6 presents the conclusion of the
results obtained and provides recommendations for future research.
12
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction to Metalloporphyrin Complexes
In the 1970s several groups, e.g., those of Collman, Baldwin, Traylor, and
Momenteau, carried out elegant studies on model metalloporphyrins with the goal of
emulating the reversible oxygen binding of hemoglobin and myoglobin. The aim of
these studies was to prevent further reaction of the iron-dioxygen complex by
hindering the irreversible formation of the µ-oxo complex via reaction with a second
molecule of the iron(II) porphyrin (Reaction 2.1). In the hemoprotein the approach of
a second molecule of iron(II) porphyrin is prevented by the steric bulk of the protein
ligand [1].
PFeII
PFeIII-O-O
PFeIII-O-O-FeIIIP
µ-peroxo
PFeII
2PFeIV=O
PFeIII-O-FeIIIP
(Reaction 2.1)
µ-oxo
Groves et al. [4] were the first to show that an iron(III) porphyrin and a
chemical oxidant, such as iodosylbenzene, would mimic many of the oxidation of
cytochrome-P450 monooxygenases. A significant difference between these models
13
and the enzymes is the presence of the protein matrix in the latter systems. The
protein binds and site-isolates the iron(III) protoporphyrin IX prosthetic group,
controls the reactivity of the active oxidant, and prevent inactivation of the enzyme
through aggregation or bimolecular self-oxidation of the iron(III) porphyrin.
The protein also controls the access of the substrate to the active oxidant and
hence the selectivity of the oxidation and it provides the hydrophobic environment
for substrate binding. The deficiencies of the model systems have been partly
overcome through structural modification of the porphyrin rings. Thus, bulky and
electron-withdrawing substituents help to prevent deactivation of the catalyst from
aggregation and self-oxidation. Further, picket-fenced, strapped, and capped
porphyrins have been developed to control the access of the substrate to the active
oxidant and thereby to introduce selectivity into the oxidation.
Recently, a number of synthetic metalloporphyrins have been intensively
developed to mimic the activity of enzymatic monooxygenases [7]. Development in
this area is based on different strategies with the aim of designing selectivity,
stability and high turnover number catalytic systems. These strategies involve
synthesis of structured metalloporphyrins, use of efficient and clean oxidants and the
search for methods to reproduce the enzyme environment responsible for the high
rates and selectivities of the natural systems [10].
In the homogeneous medium, relatively high turnover numbers can be
obtained
initially
for
the
oxygenation
reactions
catalyzed
by
synthetic
metalloporphyrin. All the different synthetic metalloporphyrin complexes used in
these catalyzed oxidation reactions can be classified in three categories. The metal
derivatives of meso-tetraphenylporphyrin, H2TPP, constitute the first-generation of
metalloporphyrin catalysts used in these oxidations. The second-generation of
tetraarylporphyrins is represented by meso-tetrakis(pentafluorophenyl) porphyrin,
H2TDCPP, and meso-tetrakis(2,6-dichlorophenyl) porphyrin, H2TDCPP,and related
ligands where huge substituents have been introduced meso-positions. The thirdgeneration is an extension of the previous idea by having bromine, chlorine or
fluorine atoms at the ȕ-positions of pyrrole ring such as meso-tetrakis-(2,6dichlorophenyl)-ȕ-octabromoporphyrin, H2Br8TDCP, meso-tetrakis-(2,4,6-trimethyl-
14
H2 Cl8TMP,
3-chlorophenyl)-ȕ-octachloromoporphyrin,
and
meso-tetrakis-
(pentafluorophenyl)- ȕ-octafluoromoporphyrin, H2F8TPFPP [30].
Figure 2.1 shows a unique metalloporphyrin structure containing alternately
perpendicular porphyrin molecules that give rise to an unprecedented twodimensional paddle-wheel-like pattern (44 topology). It was generally accepted that
the properties of metalloporphyrin mimic the cytochrome P-450 that is known as
catalyst for selective hydroxylation of inactive alkanes. As biomimetic catalysts in
the oxygenation of hydrocarbons, metalloporphyrin complexes have been largely
employed. The high efficiency of some of these catalysts makes them potentially
useful for large-scale oxidation.
N
(Z)
N
N
N
Fe
N
N
N
(Z)
N
Figure 2.1
2.2
Structure of iron(III) tetra-(4-pyridyl)-porphyrin (Fe-TPyP)
Heterogenization of Metalloporphyrins
Metalloporphyrins are well-known for their high selectivity, operating at mild
temperatures in which they are able to catalyze selective transformation of
hydrocarbons, but their use in an industrial environment is expensive and their
handling and manipulation are rather difficult [31]. On the other hand, the traditional
heterogeneous catalysts are rather robust, can operate under more severe conditions,
15
have generally good stability and are manufactured at relatively low costs. But in
comparison with the homogeneous catalysts, their selectivity in most cases is
significantly lower. It is therefore, obvious to expect that immobilizing the active site
of metalloporphyrin on the surface of heterogeneous supports may be an efficient
strategy to develop catalysts with advantages of both metalloporphyrin and
heterogeneous catalysts. The immobilization of metalloporphyrin on different
supports seems to be a good method to satisfy environmental demands and to obtain
catalysts which preserve the properties of homogeneous systems, but are more stable
and can be easily recovered.
Metalloporphyrin as the active site can be adsorbed physically and attached
chemically to active groups at the surface of supporters [1]. Metalloporphyrins
heterogenized on high-surface oxides or porous polymers in principle have the
following advantages over their homogeneous analogues:
(a)
easy separation between catalyst and product mixture;
(b)
possibility to operate in a continuous way;
(c)
no solubility limitation of the porphyrins;
(d)
possibility of interaction between the complex and the supporter;
(e)
decreased formation of porphyrin cluster, µ-oxo-dimers; and
(f)
decreased ability for auto-oxidation.
Two broad classes of supported complex catalyst have been developed. In the
first class, the metal complex is linked to the support through attachment to one of its
ligands. In the second class, reaction of a metal complex with the support results in
displacement of ligands attached to the metal and their substitution by groups that
form an essential part of the support. In both classes two broad types of support are
used namely organic polymers and inorganic oxides [32].
Supporting the metalloporphyrin could also have added benefits arising from
the structure of the support since the support provides the local environment of the
catalyst [1]. For general application the supported metalloporphyrin catalyst should
be:
16
(a)
oxidatively stable
(b)
tough and resistant to physical abrasion
(c)
reusable
(d)
resistant to metalloporphyrin leaching or removal
(e)
suitable for batch or continuous flow system
(f)
suitable for use in a wide range of solvents and conditions, and
(g)
capable of being “tailor-made” for selective oxidation.
A generally significant and sometimes critical variable is the choice of
support. For a specific application, a large number of supports of widely different
natures may be compared or the selection may be as narrow as different version of
the same material. Changing a support may completely alter the course of reaction or
prevent catalysis.
Several types of support are commercially available which can be categorized
based on their internal architecture:
(a)
Amorphous supports: metal oxides (alumina, silica), carbon
(b)
Layered supports: Clays
(c)
Microporous
supports:
zeolites
(molecular
sieves),
polymers
(crosslinked, functionalized).
2.2.1
Metalloporphyrins Supported on Molecular Sieves
Inorganic compounds such as silica gel, clays and zeolites have been
extensively investigated as support for metalloporphyrins by the encapsulation or
immobilization method [14-15] and by direct synthesis [33-35]. The encapsulation or
immobilization of metalloporphyrin complex on insoluble solid support appears to be
a good way of heterogenizing homogeneous catalysis. Such types of heterogenizedhomogeneous catalytic systems not only offer the combined advantages of
homogeneous (mild condition) and heterogeneous (easy separation) systems, but also
impose extreme shape selectivity in catalytic process [11].
17
The catalytic properties of transition metal complexes encapsulated inside the
zeolite matrix have received considerable attention in recent times. The well defined
and ordered structure of zeolites provides an ideal environment to entrap active metal
complexes or metal cluster. Inorganic complexes encapsulated in such porous
systems can even mimic natural enzymes and can therefore be termed as zeozymes.
Rosa et al. [33] and Khan et al. [34] have described the catalytic activity of iron(III)
porphyrin encapsulated in zeolite X (Figure 2.2). In another report, Skrobot et al.
[14] have used the zeolite synthesis method to synthesize zeolite Y around
manganese(III) tetra-(4-N-benzylpyridyl) porphyrin complexes.
I
Figure 2.2
FeP
Zeolite NaX (I) and iron(III) porphyrins (FeP) [34]
Among the various solid supports, the mesoporous molecular sieve MCM-41
recently synthesized by researchers in Mobil Corporation is of particular interest.
Several reports on the immobilization of porphyrin molecules onto MCM-41-type
mesoporous solids have appeared recently. Li, et al. [15] have described how [mesotetrakis(1-methyl-4-pyridinio)-porphyrinato]manganese(III)-penta-acetate complexes
were encapsulated within the channels of DMY and MCM-41 and the activity and
selectivity of these materials was reported to be high for alkene epoxidation. The
encapsulation of metal complexes inside molecular sieve MCM-41 have been studied
for oxidation of benzyl alcohol over (Fe-phen) complexes in MCM-41 [36] and
liquid-phase oxidation of n-hexane and cyclohexane over C8RuPcMCM-41 [37].
18
(a)
Mesoporous Materials MCM-41 as the Inorganic Host
Porous materials are technically used as absorbents, catalysts and catalyst
supports because of their high surface area [38]. IUPAC distinguishes between three
groups of porous materials that are classified as (i) microporous (pore size < 2 nm),
(ii) mesoporous (pore size 2-50 nm), and (iii) macroporous (pore size > 50 nm).
Zeolites are well-known and widely used microporous materials [39]. Although
zeolites
exhibit
excellent
catalytic
properties
owing to
their
crystalline
aluminosilicate network, their applications are limited by the small pore size.
Enlargement of the pore size was therefore a major objective in zeolite research.
The class of materials containing larger mesopores encompassed porous
glasses and gels such as aerosols and xerogels, and pillared, layered structures like
clays, but the drawback of these materials was their disordered pore system with
broad pore size distributions. Inorganic porous materials such as zeolites, aluminas,
silica gels and mesoporous MCM-41 molecular sieves provide new classes of
heterogeneous hosts for catalysis processes [40].
In 1992, scientists at Mobil Research and Development Corporation
discovered the M41S family of mesoporous molecular sieve [17]. The mesoporous
M41S molecular sieves include MCM-41 with a hexagonal arrangement of tubular
pores, MCM-48 with a cubic structure, and MCM-50 with a lamellar structure.
Illustrations of the mesostructures of these materials are shown in Figure 2.3. These
mesoporous materials bridge the gap between crystalline zeolites with micropores (<
13 Å) and amorphous silica gels with macropores [41]. For the first time,
mesoporous materials possessing both a regularly ordered arrangement of pores and
a narrow pore size distribution were prepared.
M41S-type molecular sieves have channel structures and have controllable
pore sizes of 1.5-10 nm in conjunction with extremely large surface areas
> 1000 m2 g-1. With the discovery of the M41S family of molecular sieves featuring
highly desirable properties, a great deal of research interest was initiated and has ever
since devoted to mesoporous molecular sieves. Recent review articles provide
comprehensive overviews on this subject [42].
19
(a)
(b)
(c)
Figure 2.3
M41S family of mesoporous materials: (a) hexagonal MCM-41;
(b) cubic MCM-48; (c) lamellar MCM-50
MCM-41 is a novel mesoporous silicate material, possessing one-dimensional
uniform pore system consisting of hexagonally arranged channels. The pore
diameters vary from 15 to 100 ǖ. Unlike zeolites, the pore walls Al-MCM-41 are
relatively thicker. The surface area of the MCM-41 materials is very high (up to 1000
m2/g), and the pore size distribution is nearly as sharp as that of conventional zeolites
as shown in Figure 2.4. MCM-41 has attracted the attention of scientists due to its
elevated specific high thermal and hydrothermal stability, possibility of controlling
its pore size and its hydrophobicity and acidity [42].
20
Sorption (Arbitrary Units)
Zeolite Y
7.8 ǖ
MCM-41
40 ǖ
Amorphous
Silica
Pore diameter (ǖ)
Figure 2.4
Horväth-Kawazoe pore size distribution for MCM-41, zeolite Y and
amorphous silica [42]
The structural model of MCM-41 is shown in Figure 2.5. Removal of the
template via exposure to air at higher temperatures (calcination), leaves long-range,
uniform, parallel, cylindrical mesoporous channels in a 2-D hexagonal array (space
group p6mm) [43].
Amorphous silica
Wall thickness ~10 ǖ
Figure 2.5
Pore diameter ~35 ǖ
Schematic of the structure of the mesoporous material MCM-41 with
cylindrical mesopores packed in a hexagonal array and amorphous siliceous pore
walls
21
The presence of hydrothermal stability and larger pore size dimensions than
zeolite has made MCM-41 as a potential catalyst for producing fine chemicals within
characteristic of larger molecules. Besides their potential for the catalytic conversion
or adsorptive separation of bulky molecules, these mesoporous molecular sieves can
also be used as host materials for spacious molecules like porphyrins or other
transition metal complexes.
2.2.2
Metalloporphyrins Supported on Polymer Matrix
The utility of polymer supported catalysts is now well-recognized because of
their ease of workup of a separation of products and catalysts, from the economical
point of view, and in application to industrial processes. Kobayashi et al. [44] has
developed polystyrene-supported Sc(OTf)3 catalyst . This new technique for binding
monomeric compounds to polymers will be applicable to the preparation of many
other polymer-supported catalysts and reagents. In general, metal-complex catalysts
are immobilized on polymers via coordinated or covalent bonds.
For the purpose of this research organic polymers can be divided into two
groups, linear and cross-linked [32]:
(a) Linear organic polymers are prepared by one of two methods: a
polycondensation or addition polymerization.
(b) Cross-linked polymers may remove some of the uncertainty of what occurs
structurally in a polymer-solvent system; however, new factors must now be
considered.
Synthetic
polymers
can
be
designed
with
pores
and
molecules
complementing each other, with highly specific recognition capabilities, similar to
those found in biological systems (e.g. enzymatic catalysis). These materials known
as porous polymers can be used as support for transition metal complexes. A variety
of linear and cross-linked organic polymer ligands have been also employed to
22
support metalloporphyrins. The extent of cross-linking of these materials affects the
flexibility of the support, which in turn affects the activity of the catalyst [1].
Tong et al. [45] have used zinc(II)-protoporphyrin as a functional monomer in
molecular imprinting-based fluorescent chemosensor for histamine. In another study,
Haber et al. [46] have described the co-oxidation of styrene and iso-butyraldehyde in
the presence of polyaniline-supported Co-, Fe-, and Mn-tetrakis (p-SO3H)PP
porphyrins in the liquid phase.
(b)
Polymer as the Organic Host
Organic polymers that have been used as supports include polystyrene,
polypropylene, polyacrylates and polyvinyl chloride. Polymers offer several
advantages over other supports [32]:
(a)
They are easily functionalized; this is particularly true of polymers
containing aryl groups.
(b)
Unlike metal oxide surfaces, most hydrocarbon polymers are
chemically inert. As a result, the support does not interfere with the
catalytic group.
(c)
Polymers, particularly poly(styrene-divinylbenzene) can be prepared
with a wide range of physical properties. As a result their porosity,
surface area and solution characteristics can be altered by varying the
degree of cross-linking.
The principal disadvantage of polymers are their poor heat transfer ability and
in many cases their poor mechanical properties which prevent them from being used
in stirred reactors in which they are pulverized. It is important in developing polymer
supported catalysts to have as well-defined and pure a support as possible. Polymer
supported catalyst has been demonstrated to be effective in many useful carboncarbon bond-forming reactions [32]. In all cases, the catalyst was recovered
quantitatively by simple filtration and reused without loss of the activity.
23
Unfortunately, heterogeneous systems involving polymers are often difficult
to synthesize and optimize and characterization is often incomplete. Many different
systems have been examined which successfully heterogenized a typically
homogeneous catalysts by copolymerizing it into the matrix of a cross-linked organic
polymer. The Gagne laboratory recently reported on a heterogeneous rhodium
catalyst (PRH), [(idppe)Rh(nbd)]BF4 immobilized within the matrix of highly crosslinked, macroporous, ethylene dimethacrylate (EDMA) polymer (Figure 2.6) [47].
P
P
Rh
Rh
P
BF4
-
P
PRh
Figure 2.6
Polymer immobilized rhodium catalyst, PRH. PRH was prepared from
the copolymerization of [(idppe)Rh(nbd)]BF4 (2 mol%) into an ethylene
dimethacrylate-based polymer (98 %) [47]
2.3
Oxidation of Benzene to Phenol
The oxidative hydroxylation of aromatics, in particular the direct oxidation of
benzene to phenol, is one of the most difficult problems in the field of organic
synthesis [25]. Phenol and its derivatives are industrially important in the synthesis
of many dyes, insecticides and compound for pharmaceuticals [48]. The existing
commercial process for the synthesis of phenol involves benzene as the starting
material. The process comprises multiple steps with cumene as an intermediate
More than 90% of the industrial production of phenol is done using the cumene
process, which consists of three steps and produces acetone as a by-product [49]. In
the first step, benzene is alkylated with propylene using phosphoric acid and AlCl3 as
24
catalyst to give rise to cumene. Cumene is then oxidized using air to give cumene
hydroperoxide which is then hydrolyzed using sulfuric acid to yield phenol. Acetone
is formed as by-product in the final step.
There are several disadvantages of this process: conversions at each step must
be kept low to attain high selectivity and corrosive and hazardous catalysts such as
H2SO4 are used. In addition, since acetone is formed as by-product, the economics of
the process is closely related to the market demand for acetone. Thus, there is a need
to replace the current commercial process by a one-step process that synthesizes
phenol from benzene.
Selective insertion of an oxygen atom into hydrocarbons, such as in the
conversion of benzene to phenol, represents a challenge with respect to the one-step
production of phenol [50]. Although a direct oxidation process of benzene to phenol
would be the most economical route, until now only the indirect manufacturing
processes have been operated.
Recently, many researchers have chosen the one-step hydroxylation of
benzene to phenol [50-52] as an alternative. However, phenol is oxidized more easily
than benzene and thus, many by-products like hydroquinone and benzoquinone are
obtained. There are three main pathways for the direct oxidation of benzene to
phenol [51].
Hydroxylation of benzene by nitrous oxide can be carried out in the gas phase
over ZSM-5 zeolites at 623–673 K with >90% phenol selectivity at 20-30% benzene
conversion [50, 52]. In these embodiments, benzene is reacted with N2O in the gas
phase at elevated temperatures to give phenol (Figure 2.7). Main problems of an
industrial application are deactivation of the catalyst by heavy coke formation and
the low phenol selectivity of nitrous oxide.
Another pathway for direct synthesis of phenol is the catalytic liquid-phase
hydroxylation of benzene using hydrogen peroxide as an oxidant. The reaction has
been carried out in acetone, methanol or acetonitrile as solvents using vanadium- or
titanium-containing heterogeneous catalysts like Ti/MCM-41 [53] or VOx/MCM-41.
25
The benzene hydroxylation by hydrogen peroxide in the presence of a VOx/MCM-41
catalyst resulted in a benzene conversion of 10% and the phenol selectivity amounted
to 38% [54].
Other attempts for the catalytic benzene oxidation have been undertaken
employing molecular oxygen both in the gas and liquid-phase. Conventional methods
of partial oxidation lead to the destruction of the aromatic ring and thus, to low
phenol selectivity [55].
OH
o
300-500 C
+
Figure 2.7
N2O
+
H-ZSM-5
N2
One-step transformation of benzene to phenol using N2O in the gas
phase
2.4
Characterization Techniques
Characterization of the catalysts were carried out by means of several
methods: X-ray diffraction (XRD), Fourier transform infrared (FTIR), ultravioletvisible diffuse reflectance (UV-Vis DR), electron spin resonance (ESR), atomic
absorption
spectroscopy (AAS),
single-point
BET
surface
area
analysis,
thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).
Luminescence and
13
C CP/MAS NMR spectroscopy techniques are used to
investigate the physicochemical properties of the polymer supported catalysts.
26
2.4.1 X-ray Powder Diffraction (XRD)
X-ray powder diffraction is an extremely useful technique in material
characterization. A lattice array of atoms can be regarded as an infinite stack of
parallel, equally space planes. Any rational plane (hkl) of the lattice array can be
chosen as the plane in question, and the whole array can be thought of as a stack of
planes parallel to this one. The principal equation used in the analysis of an X-ray
powder pattern is the Bragg’s Law, which states that:
n.λ
= 2 dhkl sinθ;
n = 1, 2,…..
(Equation 2.1)
The path difference between the incoming wave and the scattered wave must be an
integral number of wavelengths, nλ, when n is an integer; dhkl is the interplanar
spacing of the lattice and θ is single of incidence (Figure 2.8) [38]
X-ray Source
θ
θ
dhkl
d sin θ
Figure 2.8
Bragg reflection diagram [38]
The presence of distinct hk0 reflection of ordered MCM-41 mesoporous
materials in X-ray diffraction data suggests a framework with long range regularity.
The hk0 reflections can be indexed to a hexagonal lattice in MCM-41 mesoporous
molecular sieves.
27
Experimental procedure:
Powder X-ray diffraction (XRD) patterns were acquired on a Bruker D8
Advanced powder diffractometer Cu Kα radiation (λ = 1.5418 A, kV = 40, mA = 40).
Approximately 1 g of sample was carefully ground to a fine powder and then lightly
pressed between two glass slides to get a thin layer. After locating and locking
sample holder in a proper place of the analyzer, samples were measured in the 2θ
scale over 1.5 to 10o. A scanning speed of 2o and 1s step time were used. The unit
cell parameter, a0 of the hexagonal structure of MCM-41 was calculated from the
formula:
a0 = 2d100¥3
2.4.2
(Equation 2.2)
Fourier Transform Infrared Spectroscopy (FTIR)
FTIR is an important method of structure characterization giving information
on short range and long range bond order caused by lattice coupling, electrostatic and
other effects [42]. For most spectrometric measurements made using a Michelson
interferometer [56], the sample is held between the interferometer and the detector.
Therefore, both partial waves from the interferometer experience the same
attenuation and phase shift when they interact with the sample. Because the phases of
both waves are shifted by the same amount, this shift has no effect on the resultant
phase of the measured interferogram. The optical layout is shown in Figure 2.9.
A beam of radiation from the source, S, is focused on a beam splitter which is
constructed of materials such that about half the beam is transmitted to a moving
mirror which reflects the beam back to the beam splitter which then reflects part of
this beam through a sample to a detector, D. The other half of the beam from the
source is reflected from the beam splitter to a fixed mirror which reflects the beam
through the beam splitter to the detector, D, via the sample. A suitable material with
the necessary optical properties for beam splitting in the mid-infrared is KBr coated
with germanium.
28
Fixed mirror
Beam splitter
Moving
mirror
S
į/2
Sample
D
Figure 2.9
Detector
Optical layout of the Michelson interferometer (S = IR source,
D = detector)
Experimental procedure:
Infrared spectra were recorded on Shimadzu Fourier-Transformed Infrared
(FTIR) 8300 spectrometer. The technique of KBr wafer was used by mixing about
0.25 mg sample with 300 mg KBr powder and then pressed under vacuum at ca. 10
tonnes. The pellet was then put in a sample holder to determine its characteristic
peaks. IR spectra were set and detected in % transmittance rather than absorbance
unit. Twenty scans over the range of 4000 – 400 cm-1 were carried out for each
sample.
29
2.4.3 UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DR)
UV-Vis diffuse reflectance spectroscopy (UV-Vis DR) is a powerful
technique for the qualitative and quantitative determination of the reflectan spectra of
solid samples or molecules embedded on the solid surface [57]. The UV-Vis DR can
reveal the chemical valence of incorporated transition metal ion [58].
UV-Vis diffuse reflectance spectroscopy measures the amount of light
reflected from the sample surface with an integrating sphere. The data are reported as
a percent of reflectance (% R) read on the transmittance scale of the instrument and
correspond to R = I/Io where Io is the intensity of the incident light and I is the
intensity of light reflected from the sample.
Kubelka and Munk have developed a theory concerning diffuse reflectance of
light-absorbing layers on surfaces. The Kubelka-Munk equation is expressed as
R∞ =
R’∞ (sample)/R’∞ (standard)
F(R∞) = (1 - R∞)2 /2R∞ = 2.303εc/s
(Equation 2.3)
(Equation 2.4)
where R’∞ is the absolute reflectance, ε is the molar absorption coefficient, c is the
molar concentration (M), and s is the scattering coefficient. R∞ is the relative
reflectance, which is measured against a standard material such as MgO or BaSO4.
Converting the Kubelka-Munk equation into logarithmic form is one convenient way
to display reflectance spectra as shown in equation (Equation 2.5):
log F(R∞) = log ε + log (2.303 c/s)
(Equation 2.5)
Since the scattering coefficient s is practically independent of wavelength (λ),
a plot of log F(R∞) versus λ of the reflectance spectrum should be equal to the real
absorption spectrum (a plot of log ε versus λ) obtained by transmission
measurement, except for a displacement by –log 2.393c/s in the direction of the
ordinate.
30
A plot of log F(R∞) versus λ is used to portray reflectance data, and this plot
corresponds to the true adsorption spectrum because the quantity F(R∞) is linearly
proportional to the molar absorption coefficient ε as shown in Equation 2.4. More
frequently, however, reflectance spectra are often presented in the form of log (1/R∞)
or % R∞ versus λ although the quantity logs (1/R∞) in reflectance spectra is not
linearly proportional to ε. This corresponds to absorbance or percent transmittance
spectra in regular absorption spectroscopy. The quantity log (1/R∞) is often referred
to as the apparent absorbance.
The diffuse reflectance spectra of the molecules adsorbed on adsorbents such
as inorganic oxides are usually broadened compared with the adsorption spectra
obtained in solution. The absorption maxima and the molar absorption coefficients
also change depending on the interaction between the adsorbed molecule and the
adsorbent.
Experimental procedure:
UV-Vis diffuse reflectance (UV-Vis DR) spectra were recorded on Perkin
Elmer Lambda 900 spectrometer. About 0.03 g of the sample was placed on a sample
holder. After locating and locking sample holder in a proper place in the analyzer,
samples were measured in the λ (wavelength) scale of 300 - 800 nm.
2.4.4 Electron Spin Resonance (ESR)
Electron spin resonance (ESR) spectroscopy provides detailed structural
information on a variety of paramagnetic organic and inorganic samples. The ESR
technique has been frequently used to investigate the nature of the catalytic site and
its coordination number [59].
31
The application of ESR in heterogeneous catalysts studies, including
determination of oxidation states, formation of ion pairs, and monitoring of ion
migration [59]. This is important when heterogeneous systems are used to facilitate
the electron transfer process such as organized molecular assemblies and oxide
surfaces.
In this research, ESR is used to detect porphyrin π-cation radicals which are
generated by photo induced electron transfer in vesicles and mesoporous MCM-41
molecular sieves and polymer. The photoyields of porphyrin π-cation radicals can
also be clearly measured by ESR.
ESR spectroscopy is uniquely suited to the study of radiation effects. To
appreciate this uniqueness, one must realize that must molecules, especially organic
molecules, contain an even number of electron is zero in a diamagnetic.
A molecule having an unpaired electron is called a free radical. Free radicals
are necessarily paramagnetic. ESR spectroscopy can be used to detect and, in
favorable circumstances, to identify free radicals [60].
Experimental procedure:
The coordination environment of Fe-complexes in supports samples was
further confirmed by electron spin resonance (ESR) analysis recorded on a JEOL
ESR spectrometer (JES-FA100) operating in the X-band region. The microwave
power employed was 0.99800 mW, and the amplitude of magnetic field modulation
at 100 kHz was 0.2 mT. All observations were made at room temperature. Forty
milligrams of the sample taken in a quartz tube with 4mm outer diameter, evacuated
to ~10-3 Torr. The tube was sealed under vacuum and then set in the quartz Dewar
vessel fitted in the ESR cavity. Manganese (g = 2.0000) was used as a reference to
mark the g-value.
32
2.4.5 Atomic Absorption Spectroscopy (AAS)
Absorption spectroscopy is used for the qualitative and quantitative
determination of total atom in solutions. The absorbance of molecules dissolved in a
suitable solvent is then converted to atomic state measured by transmitting
monochromatic light through the solution. As a consequence of interaction between
the photons and absorbing species free atom in the flame, only a fraction of incident
beam is transmitted through the solution.
The fraction of incident light absorbed by the solution is proportional to the
concentration of an absorbing species. The absorbance in solution is defined by
Beer’s law [61],
A = εbc
(Equation 2.6)
Where A is the absorbance, ε is the molar absorption coefficient (M-1 cm-1), b is the
path length (cm) through solution, and c is the molar concentration (M) of an
absorbing species. Since the energy of the absorbed photon is characteristic of each
atom, this property is exploited for quantitative analysis. This technique results
extremely useful in catalysis laboratories for determining the atomic composition of
the catalysts [59].
Experimental procedure:
Atomic absorption spectroscopy technique was used to calculate the
percentage of iron coordinated to the ligands (TPyP). 50 mg of the sample under test,
placed in a platinum crucible, was heated at 900 oC for 1 hour using a muffled
furnace. After cooling, the sample was dissolved in 1 mL of 40 % v/v HF and
evaporated. The solid obtained was dissolved using 1 mL of 1M HCl and then
diluted with water until 25 mL. Percentage of the iron in this solution was calculated
by comparing with absorption of series of standard solution of Fe(NO3)3 using
atomic absorption spectroscopy (AAS) technique.
33
2.4.6 Single-Point BET Surface Area Analysis
The physisorption of N2 has been used to characterize the porosity of
Al-MCM-41 materials. Adsorption isotherms are classified by the IUPAC according
to the so-called BDDT scheme (Figure 2.10).
In the following work, only Type II or IV isotherms are used in the
determination of surface areas (the surface of mesopores walls) and pore size
distribution of mesopores solids. For determination of surface area are most easily
studied by means of the BET method [62].
I
II
a
III
IV
a
V
Figure 2.10
VI
The IUPAC classification of adsorption isotherms [62]
34
Experimental procedure:
Surface area of the catalysts were analyzed using nitrogen adsorption
technique, whereas for all materials were analyzed with Surface Area Analyzer
instrument (Thermo Finnigen Qsurf Series) was used to investigated only the surface
areas using single-point BET Technique. The single point equation assumes the
intercept is zero since the slope is always so much larger than the intercept.
Therefore, the utilization allows the use of one gas mixture, typically 30 % nitrogen
balance helium and results in a very determination of surface area.
2.4.7 Thermogravimetric Analysis (TGA)
Thermogravimetric analysis (TGA) was used to determine the amount of
organic occluded in the as-synthesized materials. In this research, it is relevant to
determine the amount of the organic guests molecules incorporated in the materials.
Thermogravimetric analysis, measures the change in weight of the sample, as a
function of temperature. This technique is used to determine the framework weight
of MCM-41 samples. As-synthesized MCM-41 samples typically contain remnants
of organic templates and of course of bond water.
Thermogravimetric analysis allows the analysis of volatile material given-off
from the MCM-41 when the sample undergoes a temperature ramp. The temperature
range is usually between 25 and 800 oC. A typical heating rate is degree Celsius per
minute using air as the carrier gas. Since the MCM-41 materials are usually activated
by calcination in air and stabilized under nitrogen at elevated temperatures, it is
essential to have an understanding of the effects of thermal treatment on their
chemistry and structure [63].
Calcination of as-synthesized MCM-41 materials is required to remove the
hydrocarbon templates and residues. In this experiment the weight of the samples is
measured while the temperature is increased. Commonly, two regions are observed
in which, first, water is lost, and then the organic template is burnt off. TGA may
35
also be used to measure the degree of water content. In the present study, TGA was
used as a qualitative analysis technique only.
Experimental procedure:
The thermogravimetric analysis was performed in a flow of N2 by using a
Perkin Elmer Diamond Pyris Thermal analyzer. Approximately 10 mg of the samples
under test, placed in a platinum crucible, was heated from 40 oC to 900 oC at a scan
rate of 10 oC min –1. The flow rate of nitrogen over the sample was 20 mL min-1.
2.4.8 Scanning Electron Microscopy (SEM)
The scanning electron microscope (SEM) has unique capabilities for
analyzing surfaces. SEM was used to study the surface morphologies of the bulk
particles of the materials and models information on the submicron (10 -9 – 10-6 m) to
micron (~10 -6 m) length scales. This form of imaging is based upon the low energy
(< 50 eV) secondary electron emitted from the surface of the specimen. The beam
can be concentrated to a small probe that may be deflected across the specimen using
scanning coils. The secondary electrons emitted from different parts of the specimen
are obtained. Scanning electron microscopy (SEM) provides information on the
surface topography, texture, and morphology of the specimen. It offers a great depth
of focus which facilities three-dimensional visualization of specimen surfaces [63].
Experimental procedure:
Scanning electron microscopy was performed on electron microscope Philips
XL40 under vacuum condition at 5 bar pressure. This measurement was carried out
in order to determine the morphology of the sample and the crystal size. The
36
materials samples were mounted over sample holder (stubs) using double sided tape.
The samples were coated with gold (Au) using Bio Rad Coating system at 10 -1 mbar
with current flow 30 mA for 75 seconds. Sample was then placed into SEM
instruments for scanning. Tungsten filament was used as electron sources and SEM
micrograph was recorded with 10 kV resolutions to obtain 5000x enlargement.
2.4.9 Luminescence Spectroscopy
Luminescence is common to an extremely wide range of objects of inorganic
and organic nature, and synthetic materials and, for this reason, the mechanism of
processes producing it is distinguished by great variety. A feature common to them is
luminescence glow resulting from an emission transition of anion, molecule, or a
crystal from an excited electronic state to a ground or other state with lesser energy.
The emission transition is one of two possible ways of deactivating excited
electronic states; the other being radiation less transitions resulting from interaction
with the lattice or a transfer of energy to other ions. A unique property of
luminescence that determines its applications is transformation of diverse kinds of
electromagnetic and corpuscular emission, as well as of the electric, mechanical, and
chemical energy into visible light [65].
In order to measure the binding ability of Fe-complexes in polymer support,
the luminescence was employed to determine it. The efficiency of the energy
transferred from the support to Fe-complex (Ȥ) was calculated using Equation 2.7
[66] and the experiment data:
Ȥ = 1 – (I/I0)
(Equation 2.7)
Where: I and I0 are the intensity of luminescence of support in the presence and
absence of quencher (i.e. Fe-complex), respectively.
37
Measurement of the luminescence intensities of support in the absence and in
the presence of quencher (I/I0) have confirmed the occurrence of quenching of
support in their electronically excited single state by the quencher. The quenching
process can be described by the Stern-Volmer kinetic equation expressed as a
dependence of the ratio of the luminescence intensities (I0/I) of support on the
quencher concentration [66].
Experimental Procedure:
Luminescence spectra were recorded on Perkin Elmer LS 55 spectrometer.
About 0.04 g of the sample was placed on a sample holder. After locating and
locking the sample holder in a proper place in the analyzer, samples were measured
in the emission λ (wavelength) scale of 200 to 900 nm at excitation λ = 333 nm (this
value was determined from pre-scanning of the polymethacrylic acid (PMAA)
synthestic.
2.4.10
13
C CP Magic-Angle-Spinning NMR Spectroscopy (13C CP/MAS NMR)
The most relevant prospects of the various NMR techniques as applied to
adsorption studies as swell as to the identification of surface sites have been
reviewed by several authors [65]. The principal characteristic of the NMR technique
that makes it so useful for chemical analysis of liquids and solutions is the high
resolution that allows one to observe very small atomic interactions. It is of interest
to obtain NMR spectra of the solid state for several reasons [59]. Nuclear magnetic
resonance spectroscopy investigates atomic nuclei possessing a mechanical spin, the
nuclear spin p, such as proton 1H or the stable isotope of carbon,
13
C. These nuclei
have a magnetic moment µ because of their mechanical spin and nuclear charge. Its
value is γ times the nuclear spin p, where γ is a nuclear constant called the
gyromagnetic ration:
38
µ = γp
(Equation 2.8)
For nuclei that have long spin lattice relaxation times there are two main
difficulties which limit the observation of high resolution NMR spectra of solids.
One of these is that normally the resonance lines are broadened by anisotropic
dipole-dipole interactions and quadrupole filed gradient interactions, giving rise to
line widths in the kHz range. The second problem is chemical shift anisotropy. These
anisotropic interactions are also present in liquids but are averaged to zero by rapid
Brownian motion.
For solids, a similar averaging may be realized by magic-angle-spinning
(MAS), which can eliminate dipolar and quadrupole field interaction as well as
chemical shift interaction. MAS may be also combined with cross polarization (CP)
to increase sensitivity of rare spins and long relaxation times. The importance of
nuclear magnetic resonance spectroscopy as a tool for elucidating structures is based
on the fact that the precession frequency of a spinning nucleus bonded in a molecule
depends on its molecular environment. This is called the chemical shift of the
Larmor frequencies. The spectrum of 1H or 13C Larmor frequencies of a compound is
called its 1H or 13C nuclear magnetic resonance spectrum (NMR spectrum) [67].
Experimental procedure:
MAS NMR experiments were performed using Bruker Avance 400 MHz
spectrometer. The
13
C/CP MAS NMR spectra were recorded with a recycle delay of
5.0 s, number of transient of 2000 and spinning rate of 7 kHz. The chemical shifts of
13
C were referenced to TMS.
39
CHAPTER 3
ENCAPSULATION OF IRON(III)-PORPHYRIN WITHIN ORDERED
MESOPOROUS Al-MCM-41
3.1
Direct Synthesis of Mesoporous Molecular Sieve Al-MCM-41
The basic molar composition of Al-MCM-41 described in this chapter was
6SiO2 : 0.3NaAlO2 : CTABr : 1.5 Na2O : 0.15 (NH4)2O : 250H2O. In this work, AlMCM-41 sample with the SiO2 to Al2O3 ratio of 20 was prepared according to the
following procedure. First, a clear solution of sodium silicate was prepared by
combining 2.595 g of 1.00 M aqueous NaOH solution (pellet from MERCK) with
10.015 g rice husk ash (90 wt% SiO2) and the resulting solution (mixture A) was
then heated under stirring for 2 hours at 80 °C. A mixture of 1.05 g of 25 wt%
aqueous NH3 solution (MERCK), 9.1115 g of cetyl N, N, N, -trimethyl ammonium
bromide (CTABr) (Fluka) and 1.417 g of NaAlO2 (54 wt% Al2O3, Riedel-de Haen
were put in a polypropylene bottle and the mixture (mixture B) was then heated with
stirring for 1 hour at 80 °C. Subsequently, mixture B was added dropwise to a
polypropylene bottle containing mixture A with vigorous stirring at room
temperature. After stirring for 1 hour at 90 ºC, the gel mixture in the bottle was
heated to 97 °C for 24 hours. The CTA-aluminosilicate gel was then suddently
cooled to room temperature. The pH of the reaction mixture was then adjusted to
10.2 by adding 25 wt% acetic acid (CH3COOH) (MERCK). Repeated pH
adjustments following the work of Kim et al. [67], was performed in order to
increase thermal stability and textural uniformity of the product. The heating and pH
40
adjustment procedures were repeated two times. The precipitated product, assynthesized Al-MCM-41 containing CTA-template was filtered, washed thoroughly
with doubly-distilled water and dried in an oven at 97 °C. Al-MCM-41 was calcined
in air under static conditions in a muffled furnace. The calcination temperature was
increased from room temperature to 550 °C for 10 hours and maintained at 550 °C
for 6 hours. The mesoporous materials (as-synthesized and calcined Al-MCM-41)
obtained have been characterized by XRD, FTIR and TGA techniques, according to
section 2.4.
3.2
Preparation of Iron(III)-Tetra (4-Pyridyl) Porphyrin (Fe-TPyP)
Iron insertion into TPyP was conducted by refluxing at 100 °C of TPyP
(1 mmol) and FeCl3 anhydrous (1 mmol) in ethanol (30 mL) in an oil bath for 1 hour
(see Figure 3.1). The solution was then filtered while still hot, washed with water and
dried under vacuum. The Fe-TPyP obtained was characterized by FTIR and UV-Vis
DR spectroscopies techniques, according to section 2.4.
3.3
Preparation of Fe-TPyP/Al-MCM-41
Fe-TPyP/Al-MCM-41 was synthesized via a slight modification of the
method of Li et al. [15]. A suspension of Al-MCM-41 (0.150 g) in methanol
containing Fe-TPyP (5: 10; 25; 50; and 100 ȝmol) was stirred for 24 hours at 20 °C.
The resulting materials were filtered and washed with methanol until the filtrate
became colorless. The solid obtained was dried at 100 °C for 4 hours which afforded
Fe-TPyP. The material was characterized by XRD, FTIR, UV-Vis DR, ESR, AAS,
Single-point BET Surface area analysis, TGA and SEM, according to section 2.4.
Figure 3.2 shows schematically the procedure for encapsulating iron porphyrin
complexes in ordered mesoporous Al-MCM-41, through impregnation of ironporphyrin complex into Al-MCM-41 mesopores.
41
N
TPyP
(Z)
N
N
H
N
N
H
N
N
(Z)
N
T = 100 °C,
FeCl3,
Ethanol
FeCl3
Ethanol
1 hour
N
Fe-TPyP
(Z)
N
N
N
N
Fe
N
N
(Z)
N
+
2H+ (aq)
Figure 3.1
Reaction of TPyP with FeCl3 in ethanol in the synthesis of iron-
porphyrin complexes
42
Al-MCM-41
Fe-TPyP
T = 20 °C, 24 hours
N
(Z)
N
N
N
Fe
N
N
N
Fe-TPyP/Al-MCM-41
(Z)
N
Figure 3.2
Theoretical encapsulation of Fe-TPyP within ordered mesoporous
Al-MCM-41
3.4
Results and Discussion
3.4.1 Characterization of Al-MCM-41
The FTIR spectra of the mid-infrared region of Al-MCM-41 samples before
and after calcination are shown in Figure 3.3. The mid-infrared region from 400–
1400 cm-1 contains vibrations due to the framework structure of Al-MCM-41.
43
796
458
958
1475
1388.
1226
2923
Transmittance / a.u
3440
2869
1639
(a)
1081
3443
463
793
961
1624
1066
(b)
4000
2000
1500
1000
500
Wavenumber / cm-1
Figure 3.3
FTIR spectra of (a) as-synthesized and (b) calcined samples
Al-MCM-41
of
44
It in generally known that MCM-41 materials have properties between
amorphous materials and zeolites. According to Chen et al. [54], the IR spectrum
indicated that MCM-41 exhibit framework vibration similar to those of amorphous
materials. Before calcination, the IR spectrum of Al-MCM-41 exhibits a broad peak
at around 3440 cm-1, assigned to hydroxyl stretching of physically adsorbed water.
Peaks observed at 2923, 2869 and 1475 cm-1 are assigned to symmetric C-H and
asymmetric CH2 vibrations of the surfactant molecules. After calcination at 550 °C,
all the bands which belong to the organic groups are no longer observed in the IR
spectrum proving the complete removal of the surfactant template (CTABr).
The powder X-ray diffractogram patterns of the as-synthesized and calcined
Al-MCM-41 samples are shown in Figure 3.4. An intense peak representing the
(100) diffraction is observed on both samples and in good agreement with reported
patterns from MCM-41 materials [17]. Peaks corresponding to (110), (200) and (210)
reflections which are characteristic of hexagonal structure can be seen clearly, but are
not well resolved in the case of as-synthesized Al-MCM-41.
The four peaks observed on the calcined Al-MCM-41 sample suggest that
highly ordered mesoporous structure was obtained. The unit cell parameters and dspacing values of the Al-MCM-41 samples are given in Table 3.1. The hexagonal
unit cell parameter a0 was calculated from the equation a0=2d 100¥3. The presence of
a single intense peak at 2.135° 2ș indicates that the as-synthesized Al-MCM-41
possesses regular mesopores [17].
For the calcined sample, the intensity of the peaks becames stronger and the
ș value was reduced from ca. 2.135 to 2.202°, indicating a decreased in the lattice
parameter, owing to the removal of the organic surfactant template from the channels
by calcination at 550 °C, and subsequent condensation process of silanol groups in
the MCM-41 walls. Comparing the diffraction peak intensity and peak width, it is
obvious that the calcined Al-MCM-41 seems more highly ordered than the assynthesized Al-MCM-41, suggesting that the degree of ordering is improved by the
removal of the surfactant template.
45
(100)
Calcined Al-MCM-41
hkl
d(nm)
100
110
200
210
4.009
2.310
2.019
1.520
Relative Intensity / a.u
(110)(200)
(210)
(100)
As-synthesized Al-MCM-41
(110)(200)
1.5
2
3
4
hkl
d(nm)
100
110
200
210
4.135
2.403
2.088
1.578
(210)
5
6
7
8
9
10
ș / °
Figure 3.4
samples
XRD patterns of the as-synthesized and calcined Al-MCM-41
46
Table 3.1 : XRD data and lattice parameter of the Al-MCM-41 samples
ș / o
d100 / nm
Unit Cell
Parameter,
a0 /nm
As-synthesized
2.135
4.135
4.780
Calcined
2.202
4.009
4.635
Sample
The thermogravimetric analysis (TGA) of as-synthesized and calcined
samples of Al-MCM-41 was carried out at 50 °C to 900 °C, under flowing nitrogen
at the rate of 10 °C/minute. The TGA profiles of as-synthesized and calcined samples
of Al-MCM-41 samples are shown in Figure 3.5.
100
90
(b)
80
(i)
Weight / %
70
(ii)
60
50
(iii)
40
(a)
30
20
10
0
300
600
900
Temperature / oC
Figure 3.5
Al-MCM-41
TGA thermograms of (a) as-synthesized and (b) calcined samples of
47
The thermograms of the as-synthesized sample show the regions of weight
loss as depicted in Figure 3.5(a). The first region occurs at temperatures around 50 to
150 °C, which can be reasonably assigned to desorption of water. Above 150 °C,
breakage, decomposition and thermal desorption of organic fragments occur.
The remaining part corresponds to organic material whose mass loss is
related to three exothermal stages: (i) between 150–285 °C: decomposition of the
surfactant; (ii) large weight change between 285–490 °C: breaking of the
hydrocarbon chain) and (iii) between 490–620 °C: combustion of the residual
surfactant and water loss associated with condensation of silanol groups.
Thermogravimetric analysis curve of the calcined form of Al-MCM-41 clearly lacks
inflection points indicative of template weight loss (Figure 3.5 (b)). This result
suggests that the cationic template has been removed almost completely from the
framework of Al-MCM-41.
3.4.2
Characterization of Iron(III)-Tetra (4-Pyridyl) Porphyrin
The dark-purple solid of iron(III)-tetra (4-pyridyl) porphyrin (Fe-TPyP)
obtained was characterized by using FTIR and UV-Vis DR spectroscopies. The FTIR
spectra of the TPyP (commercial) and Fe-TPyP are shown in Figure 3.6 and the
major FTIR bands of TPyP and Fe-TPyP complexes are tabulated in Table 3.2.
In the FTIR spectrum of TPyP, the broad peak at 3431 cm-1 is related to the
stretching of the N-H bonds of the aromatic. Another characteristic peak is the =C-H
stretching of the aromatic observed at 3100–2900 cm-1. The strong peak at
wavenumber 1595 cm-1 is due to the C=N conjugation of the aromatic; the C=C and
C-C stretching are assigned to the peaks at 1632 cm-1 and 1468 cm-1, respectively,
and peaks at 1000–700 cm-1 show the C-H bonds of the aromatic.
48
873
721
1468
1595
Transmittance / a.u
3431
3082
1632
(a)
724
1464
1630
1591
3413
2935
878
(b)
4000
2000
1500
1000
Wavenumber / cm-1
Figure 3.6
FTIR spectra of (a) TPyP and (b) Fe-TPyP complexes
500
49
On introduction of iron in the porphyrin, a shifting of the peaks at 1595 cm-1
(C=N bond), 1632 cm-1 (C=C bond) and 1468 cm-1 (C-C bond) in IR spectrum of
TPyP to lower values is observed in the IR spectrum of Fe-TPyP. This is a clear
indication of the incorporation of iron in the porphyrin.
Table 3.2 : Assignment of FTIR bands of TPyP and Fe-TPyP complexes
Wavenumber / cm-1
Characteristic Vibration
TPyP
Fe-TPyP
N-H bonds of aromatic
3431
3413
=C-H bonds of aromatic
3082
3083 and 2935
C=C bonds
1632
1630
1595 and 1553
1591 and 1541
C-C bonds of aromatic
1468
1464
C-H bonds of aromatic
873 and 721
878 and 724
C=N conjugate of aromatic
The dark-purple colour of the samples indicated that iron(III) was present in
the porphyrin, and this was confirmed by UV-Vis diffuse reflectance spectroscopy
(UV-Vis DR). The UV-Vis DR spectra of TPyP and Fe-TPyP are given in Figure
3.7. The UV-Vis DR spectra of iron(III) compounds with porphyrin ligands
coordinated exhibit attributed to charge transfer porphyrin ĺ iron transitions. The
new peaks at 424 nm in Figure 3.7(a) reveals that iron(III)-porphyrin has been
prepared. This peak is attributed to internal ʌ ĺ ʌ* transitions of the ligand
porphyrin.
In addition, the UV-Vis DR spectrum of Fe-TPyP presents absorption bands
at 510, 585 and 644 nm. The three peaks present in the region of 500–700 nm are
typical of those of high-spin Fe(III) porphyrins [3]. The three peaks in this region are
also attributed to d-d transitions of the iron(III).
50
510
585
644
K-M / a. u
424
(a)
(b)
400
500
600
700
800
Wavelength / nm
Figure 3.7
UV-Vis DR spectra of (a) Fe-TPyP and (b) TPyP
3.4.3 Characterization of Fe-TPyP/Al-MCM-41
Al-MCM-41 encapsulated Fe-TPyP complexes have been prepared by the
method of Li et al. [15]. The solid obtained has been characterized by XRD, FTIR,
UV-Vis DR and ESR along with AAS, single-point BET surface area, TGA and
SEM.
Figure 3.8 shows the IR spectra of the free Fe-TPyP complex, the pure
Al-MCM-41 and the Al-MCM-41 encapsulated Fe-TPyP complex. The major bands
of Al-MCM-41 dominate the 1300–400 cm-1 region of the spectrum of Fe-TPyP/
Al-MCM-41. However, the presence of TPyP is obvious, because bands originating
from Fe-TPyP were observed in the 1700–1300 cm-1 region of the spectrum.
51
C-C
724
1466
C=C
878
1650
3431
2921
(a)
3443
463
1624
961
C=N
793
Transmittance / a.u
1591
(b)
C=N
798
1081
C-C
969
723
663
1464
1404
1383
1637
1595
(c)
1080
3446
463
C=C
2000
1500
1000
500
Wavenumber / cm-1
Figure 3.8
FTIR spectra of (a) Fe-TPyP complexes, (b) Al-MCM-41 and
(c) Fe-TPyP/Al-MCM-41
52
The spectrum of Fe-TPyP/Al-MCM-41 exhibits bands at 1637 cm-1 (C=C
bond), 1404 cm-1 (C-C bond) and 1595 cm-1 (C=N bond), corresponding to stretching
vibrations of phenyl group of the porphyrin. Compared with the spectrum of the pure
Al-MCM-41 sample, the observation of those bands clearly indicate that Fecomplexes have been successfully encapsulated in the channels of Al-MCM-41 [15].
The IR bands of encapsulated complexes are weak due to low concentration of
Fe-TPyP in Al-MCM-41.
Figure 3.9 shows the IR spectrum of Fe-TPyP/Al-MCM-41 with various
amounts of Fe-TPyP loading. All the samples show identical bands in the region
1700–1300 cm-1. The bands at 1595 and 1553 cm-1 (C=N bond), 1637 cm-1 (C=C)
show increasing intensity with the increase in the amount of Fe-TPyP loading.
As the amount of Fe-TPyP loading increases from 10 ȝmol – 100 ȝmol, the
peaks in the 1700–1300 cm-1 region due to the vibrations of C=N and C=C of the
porphyrin ligand become increasingly prominent. On the other hand, for the sample
with 5 ȝmol of Fe-TPyP loading, those peaks are not observed may be caused by the
low level incorporation of Fe-TPyP in Al-MCM-41.
X-ray powder diffraction (XRD) patterns of the encapsulated Fe-TPyP are
given in Figure 3.10, which are consistent with the XRD pattern for unloaded
molecular sieve Al-MCM-41 without any peaks arising from Fe-TPyP. Results of the
X-ray diffraction study also indicate that the Al-MCM-41 support remains
structurally unchanged and believed that the iron-porphyrin is dispersed molecularly
within the mesoporous channels.
A typical XRD pattern of the Al-MCM-41 encapsulated Fe-TPyP complex
shows three weak peaks which can be assigned to (110), (200) and (210) indicating
that after encapsulation the long range order of the inorganic host, Al-MCM-41, has
diminished, but fundamentally the mesostructure of the host material is still
maintained. The reduction in intensity of the (100) diffraction peak became
noticeable when the Fe-TPyP loading reached 100 ȝmol, but the basic structure of
Al-MCM-41 was still maintained even for the sample with 100 ȝmol of Fe-TPyP
loading.
53
Fe-TPyP =100ȝmol
C=C
C=N
C=C
C=N
C-C
Fe-TPyP =50ȝmol
C-C
Transmittance / a.u
Fe-TPyP =25ȝmol
C=C C=N
C-C
Fe-TPyP =10ȝmol
C=C C=N
C-C
Fe-TPyP =5ȝmol
4000
3000
2000
1000
500
Wavenumber / cm-1
Figure 3.9
FTIR spectra of Fe-TPyP/Al-MCM-41 with various amounts of
Fe-TPyP loadings
54
(100)
Fe-TPyP =100ȝmol
(110) (200)
(210)
Fe-TPyP =50ȝmol
Relative Intensity / a.u
Fe-TPyP =25ȝmol
Fe-TPyP =10ȝmol
Fe-TPyP =5 ȝmol
Fe-TPyP =0 ȝmol
1.5
2
3
4
5
6
7
8
9
10
ș / °
Figure 3.10
XRD patterns of Al-MCM-41 and Fe-TPyP/Al-MCM-41 with various
amounts of Fe-TPyP loadings
55
It was also noted that the peaks shift to higher 2ș angles with a corresponding
decrease in the a0 values as the amount of Fe-TPyP loading is increased (Table 3.3).
The decreased unit cell parameter with respect to Al-MCM-41 can be explained by
the incorporation of iron(III)-porphyrin into the mesoporous channel of Al-MCM-41.
Table 3.3 : XRD data of iron-containing Al-MCM-41 catalysts
Fe-TPyP
Samples
loading /
ș / o
unit cell
d 100 / nm parameter,
a0 / nm
ȝmol
Al-MCM-41
-
2.202
4.009
4.635
Fe-TPyP/Al-MCM-41-5
5
2.205
4.003
4.628
Fe-TPyP/Al-MCM-41-10
10
2.208
3.998
4.622
Fe-TPyP/Al-MCM-41-25
25
2.210
3.994
4.617
Fe-TPyP/Al-MCM-41-50
50
2.213
3.988
4.610
Fe-TPyP/Al-MCM-41-100
100
2.214
3.986
4.608
Figure 3.11 show the UV-Vis DR spectrum of Fe-TPyP and Fe-TPyP/
Al-MCM-41. The Al-MCM-41 encapsulated Fe-TPyP shows the Soret band at
414 nm, which are blue-shifted when compared to the spectrum of Fe-TPyP, and the
three peaks in the range of 500–700 nm (517, 589 and 644 nm) are typical of highspin Fe(III)-porphyrins [68-69]. The occurrence of the absorption maximum at 589
nm can be assigned to the axial electrostatic interaction between the iron-porphyrin
and the anionic Al-MCM-41 pore surfaces, indicating the incorporation of Fe-TPyP
in the support [33].
Figure 3.12 depicts the UV-Vis DR spectra of Fe-TPyP/Al-MCM-41 with
various amounts of Fe-TPyP loading. Especially interesting is that even with the FeTPyP loading as low as 5 µmol, the bands around 414–420 nm (Soret), 589 nm, and
the three peaks in the 500–700 nm could still be observed in the UV-Vis DR spectra.
This implies that UV-Vis DR spectroscopy is a very sensitive characterization
technique and has proven to be a powerful tool for identifying the electronic structure
of the iron complex formed inside the channels of Al-MCM-41 in the present study.
56
K-M / a. u
462
589
517
414
(a)
644
(b)
400
500
600
700
800
Wavelength / nm
Figure 3.11
UV-Vis DR spectra of (a) Fe-TPyP and (b) Fe-TPyP/Al-MCM-41
The local structure of iron(III) species in molecular sieve materials also can
be easily detected by other techniques such as ESR. Fe-TPyP displays similar ESR
spectrum with that of high-spin Fe(III) signal at g = 1.984 (Figure 3.13(a)). As
depicted in Figure 3.13(b), two different signals occur in the ESR spectrum of the
Fe-TPyP/Al-MCM-41 sample. The broad signal at g = 4.284 is assigned to Fe(III) in
distorted framework tetrahedral coordination, whereas the signal at g = 2.00067
belongs to high-spin Fe(III)-porphyrin. A radical signal at g = 2.00067 was also
observed indicating the formation of Fe-complex intra mesoporous cavity [70].
Figure 3.14 shows the ESR spectra of Fe-TPyP/Al-MCM-41 with different
Fe-TPyP loadings. As one can see, an increase content from 5–100 ȝmol of
Fe-TPyP is accompanied by a gradual increase in intensity of the ESR line in the
region of the magnetic field at g = 2.0006.
57
Fe-TPyP =100ȝmol
K-M / a. u
Fe-TPyP =50ȝmol
Fe-TPyP =25ȝmol
Fe-TPyP =10ȝmol
Fe-TPyP =5ȝmol
400
500
600
700
800
Wavelength / nm
Figure 3.12
UV-Vis DR spectra of Fe-TPyP/Al-MCM-41 with various of amount
of Fe-TPyP loading
Intensity / a. u
58
(a)
g = 1.984
g = 4.284
g = 2.00067
100
200
300
400
(b)
500
B / mT
Figure 3.13
ESR spectra of (a) Fe-TPyP and (b) Fe-TPyP/Al-MCM-41
59
g = 2.00067
Fe-TPyP=100ȝmol
Intensity / a. u
Fe-TPyP=50ȝmol
Fe-TPyP=25ȝmol
Fe-TPyP= 10ȝmol
Fe-TPyP=5ȝmol
100
200
300
400
500
B / mT
Figure 3.14
ESR spectra of Fe-TPyP and Fe-TPyP/Al-MCM-41 with various
Fe-TPyP loadings
60
Table 3.4 gives the values obtained from atomic absorption measurements of
the Fe content of Fe-TPyP/Al-MCM-41 samples. It is seen that the increase of iron
content corresponds with the increase of FeTPyP loaded in Al-MCM-41.
Table 3.4 : Iron content (%Fe) of Fe-TPyP/Al-MCM-41 with different amount of
Fe-TPyP loading
Sample
Fe (%)
Fe-TPyP/Al-MCM-41-100 (Fe-TPyP = 100ȝmol)
0.22
Fe-TPyP/Al-MCM-41-50 (Fe-TPyP = 50ȝmol)
0.17
Fe-TPyP/Al-MCM-41-25 (Fe-TPyP = 25ȝmol)
0.15
Fe-TPyP/Al-MCM-41-10 (Fe-TPyP = 10ȝmol)
0.10
Fe-TPyP/Al-MCM-41-5 (Fe-TPyP = 5ȝmol)
0.08
Table 3.5 shows the surface properties of Al-MCM-41-supported Fe-TPyP
catalysts determined from surface area analysis. The BET surface area was decreased
with increasing amount of iron loading up to 100 ȝmol, due to the filling of pores by
Fe-TPyP.
Table 3.5: Surface properties of Al-MCM-41-supported Fe-TPyP with different
amount of Fe-TPyP loading
Samples
Surface area (m2g -1)
Al-MCM-41
813
Fe-TPyP/Al-MCM-41-5 (Fe-TPyP = 5 ȝmol)
734
Fe-TPyP/Al-MCM-41-10 (Fe-TPyP = 10 ȝmol)
652
Fe-TPyP/Al-MCM-41-25 (Fe-TPyP = 25 ȝmol)
471
Fe-TPyP/Al-MCM-41-50 (Fe-TPyP = 50 ȝmol)
383
Fe-TPyP/Al-MCM-41-100(Fe-TPyP=100 ȝmol)
217
61
Figure 3.15 shows the thermogravimetric analysis curves of Al-MCM-41 and
Fe-TPyP/Al-MCM-41. Exothermic weight losses were observed for all the materials
at temperatures below 150 °C, which correspond to the loss of physisorbed water.
The parent host material (Al-MCM-41) exhibits an additional exothermic weight loss
at over 300 °C. The thermogram of Fe-TPyP/Al-MCM-41 sample shows the weight
loss extends in the region 400–500 °C and 500–600 °C, attributed to the
decomposition or burning of the iron-porphyrin.
In the thermogravimetric curves obtained, it was possible to observe that for
free Fe-TPyP, the content of organic matter (porphyrin) was around 48% and for the
encapsulated Fe-TPyP/Al-MCM-41, the content was found to be much lower (around
12%), related to dry matter basis.
100
90
(a)
Water loss
80
Weight / %
70
60
(b)
50
40
30
20
Decomposition of
organic matter
(porphyrin)
10
0
300
600
(c)
900
Temperature / oC
Figure 3.15
TGA thermograms of (a) calcined Al-MCM-41, (b) Fe-TPyP/
Al-MCM-41 and (c) Fe-TPyP complexes
62
The size and morphology of the Al-MCM-41 and Fe-TPyP/Al-MCM-41
materials obtained by encapsulation of iron-porphyrin within mesoporous material
Al-MCM-41 (Fe-TPyP/Al-MCM-41) were investigated by scanning electron
microscopy. The SEM micrographs of these materials are presented in Figure 3.16.
(a)
(b)
Figure 3.16
Al-MCM-41
Scanning electron micrographs of (a) Al-MCM-41 and (b) Fe-TPyP/
63
All the samples do not have well defined hexagonal structure. Further,
aggregates without regular shapes are observed in agreement with previous reports
[71] for metal-complexes incorporated materials indicating a slight reduction in
hexagonal symmetry of Al-MCM-41 due to metal-complex incorporation. The
micrographs of Fe-TPyP/Al-MCM-41 also confirm the uniformity of particle size,
but after incorporation of iron-porphyrin, the particle size has become smaller than
that of the pure Al-MCM-41. This observation lends to support the fact that there
was a decrease of the surface area of Al-MCM-41 after incorporation of Fe-TPyP
(see Table 3.4).
The proposed interaction between the negatively charged aluminium in the
framework of Al-MCM-41 and the Fe-center of the porphyrin complex is presented
in Figure 3.17. The strong electrostatic interaction between Fe and the support has
been reported to prevent leaching of the Fe-TPyP species into solution during the
oxidation reaction [19].
N
(Z)
N
N
N
Fe
N
N
N
(Z)
N
Electrostatic
Interaction
H+
O
O
Si
_
Al
O
O
Si
Al-MCM-41
Figure 3.17
interaction
Proposed mechanism of Fe-TPyP complex-Al-MCM-41 support
64
CHAPTER 4
IMMOBILIZATION OF IRON(III)-PORPHYRIN
IN POLYMETHACRYLIC ACID
4.1
Polymethacrylic acid as Organic Support
Synthetic
polymers
can
be
designed
with
pores
and
molecules
complementing each other, with highly specific recognition capabilities, similar to
those found in biological systems (e.g. enzymatic catalysis). These materials known
as porous polymers can be used as support for transition metal complexes [72].
Organic polymers that have been used as supports include polystyrene,
polypropylene, polyacrylates and polyvinyl chloride.
Methacrylic acid (MAA) is a kind of important monomer used for
synthesizing functional polymer. PMAA and its copolymers are widely used as paint,
adhesive and thickener. The structure of polymethacrilic acid is shown in Figure 4.1.
CH3
CH2
O
Figure 4.1
C
CH3
CH2
OH O
C
CH2
OH
Structure of polymethacrylic acid (PMAA)
65
Polymethacrylic acid is also used as an enteric-coating polymer in the
pharmaceutical industry because of its carboxylic groups that can transform to
carboxylate groups in the pH range 5–7 by salt formation with alkali or amines.
PMAA contains carboxyl group which is strongly hydrogen-bonded, hence affecting
the enthalpy of PMAA anhydridization [73].
4.2
Synthesis of Polymethacrylic acid (PMAA)
Polymethacrylic acid was prepared using the method of Tamayo et al. [74].
Monomer methacrylic acid (MAA) (2 mmol) and toluene (6 mL) were placed into a
25 mL glass tube and the mixture was left in contact for 10 minutes. Subsequently,
Ethylene glycol dimethacrylate(EGDMA) (10 mmol) and 2. 2’-azobis (2-methyl
propionitrile) (AIBN) (15 mg) were added. The glass tube was sealed and
thermostated at 60 °C in an oil bath to start the polymerization process. After 24
hours, the obtained samples were air dried and weighted. The polymer obtained
characterized by FTIR, TGA, Luminescence and 13C CP/MAS NMR techniques.
4.3
Synthesis of Fe-TPyP/PMAA
Fe-TPyP/PMAA was prepared using the same procedure as described in
Figure 4.2. Fe-TPyP (5; 10; 25; 50 and 100 µmol), toluene (6 mL) and MAA
(2 mmol) were placed into a 25 mL glass tube and the mixture was left in contact for
10 minutes. Subsequently, EGDMA (10 mmol) and AIBN (15 mg) were added. The
glass tube was sealed and thermostated at 60 °C in an oil bath to start the
polymerization process. After 24 hours, the obtained micro-spheres were air dried
and weighted. Characterization of samples was done using FTIR, UV-Vis DR,
13
C CP/MAS NMR, AAS and luminescence spectroscopies, TGA, single-point BET
surface area analysis, SEM and ESR techniques. Figure 4.2 shows the general route
to immobilize metalloporphyrin in polymer [75].
66
Prearrangement
Solvent
MAA
Fe-porphyrin
Cross linker
Polymerization,
T = 60 °C for 24h
+
initiator
Fe-porphyrin suported on
Polymethacrylic acid
(PMAA)
Figure 4.2
Schematic representation of the procedure of synthesis of composite
Fe-porphyrin-polymethacrylic acid. Methacrylic acid (MAA) monomers assemble
with the Fe-porphyrin, followed by cross-linking polymerization [75]
4.3 Results and Discussion
4.3.2
Characterization of Polymethacrylic acid (PMAA)
Polymethacrylic acid (PMAA) was prepared following the procedure of
Tamayo et al.[74]. The polymer was prepared by polymerizing functional monomer,
crosslinker and initiator at 60 °C for 24 hours. The white powders obtained have
been characterized using FTIR, TGA, luminescence spectroscopy and
NMR.
13
C CP/MAS
67
Figure 4.3 shows the IR spectrum of the as-synthesized PMAA described
previously in section 4.2. Signals observed at 3441, 1724, and 1157 cm-1 are assigned
to O-H bond, C=O bond and C-O bond, respectively [76]. These peaks indicate that
4000
2000
1157
1724
3441
1458
2955
Transmittance / a.u
the polymethacrylic acid have been successfully prepared.
1500
1000
500
Wavenumber / cm-1
Figure 4.3
FTIR spectrum of as-synthesized polymethacrylic acid (PMAA)
The results of the thermal degradation of PMAA in flowing nitrogen (Figure
4.4) shows that the first endothermic weight loss below 150 °C and in 150 – 250 °C
temperature range is due to the release of adsorbed water through the formation of
intra- and inter- molecular anhydride links and also to the decarboxylation of a
fraction of the –COOH groups by which CO2 is formed. In the second degradation
stage, the polymer decomposes with the elimination of CO and CO2 by way of
abundant backbone scission and formation of a small concentration of unsaturation
[77].
The luminescence emission spectrum of PMAA under excitation at
is shown in Figure 4.5. The polymer exhibits an emission band at 574 nm.
330 nm
68
100
90
80
70
Weight / %
60
50
40
30
20
10
0
300
600
900
o
Temperature / C
Figure 4.4
TGA thermogram of as-synthesized polymethacrylic acid (PMAA)
Intensity / a. u
574
333
300
400
500
600
700
Wavelength / nm
Figure 4.5
The luminescence exitation and emission spectra of as-synthesized
polymethacrylic acid (PMAA) (Ȝex = 333 nm, Ȝem = 574 nm)
69
C
* Impurities
CH3
CH2
COOH
*
*
*
200
*
150
100
50
0
Chemical shift / ppm
13
Figure 4.6
C CP/MAS NMR spectrum of as-synthesized polymethacrylic acid
(PMAA)
The
13
C CP/MAS NMR spectrum of as-synthesized PMAA is shown in
Figure 4.6. The spectrum shows four chemical shifts due to the presence of four
different types of carbon and the assignment of each peak is given in Table 4.1.
Table 4.1: Assignment of 13C CP/MAS NMR spectrum of PMAA [78]
Types of C
Chemical shift, į (ppm)
-CH3
16.8
C
43.4
=CH2
60.8
-COOH
173.6
70
4.3.3
Characterization of Fe-TPyP/PMAA
The Fe-TPyP catalysts immobilized in polymethacrylic acid were prepared
following the procedure for the preparation of polymethacrylic acid, by addition of
Fe-TPyP during the polymerization process. The products were characterized using
FTIR, UV-Vis DR, ESR, Luminescence and
13
C CP/MAS NMR spectroscopies,
AAS, single-point BET surface area analysis, TGA and SEM techniques.
Figure 4.7 above shows the IR spectra of Fe-TPyP complexes, as-synthesized
polymethacrylic acid and the polymethacrylic acid supported Fe-TPyP complexes.
Comparison of the peaks at 1724 cm-1 (C=O), 1636 cm-1 (C=C) and 1452 cm-1 (C-C)
in the spectrum of polymethacrylic acid supported Fe-TPyP complex with those of
the as-synthesized polymethacrylic acid at 1728 cm-1 (C=O) and 1159 cm-1 (C-H)
clearly indicate that Fe-TPyP has been successfully anchored on the polymer.
Furthermore, the IR peaks observed in the spectrum of PMAA at 3441, 1724,
and 1157 cm-1, assigned to O-H bond, C=O bond and C-O bond [76], respectively,
were shifted to higher values in the spectrum of the polymethacrylic acid supported
Fe-TPyP complex. The shifts to higher wavenumbers are consistent with the
expected shift when Fe-TPyP is immobilized in the polymer. This shows some
chemical interaction occurs between PMAA and Fe-TPyP.
The PMAA supported Fe-TPyP has been characterized by UV-Vis DR
spectroscopy and the spectra of Fe-TPyP and Fe-TPyP/PMAA are given in Figure
4.8. The highly conjugated porphyrin macrocycle shows an intense absorption at
around 418 nm (the Soret Band) as well as several weaker absorptions (Q bands) at
higher wavelengths (500 to 700 nm).
On the other hand, Fe-TPyP exhibts a broad single band at 418 nm and three
typical bands attributed to high spin Fe(III)porphyrin species in the region 500 – 700
nm (bands at 517, 590 and 644 nm). The results of the UV-Vis DR analysis have
shown that the bands at 589 nm in the spectrum of Fe-TPyP/PMAA corresponds with
the axial coordination of the Fe-TPyP to OH-containing PMAA [33].
71
878
724
1464
3413
3083
1630
(a)
3441
1458
Transmittance / a.u
1591
(b)
4000
2000
1049
1159
1452
1728
3452
1636
1157
1724
(c)
1500
1000
500
Wavenumber / cm-1
Figure 4.7
FTIR spectra of (a) Fe-TPyP complexes, (b) as-synthesized PMAA
and (c) Fe-TPyP/PMAA
72
510
585
644
424
K-M / a. u
418
(a)
517
400
590
500
644
600
(b)
700
Wavelength / nm
Figure 4.8
UV-Vis DR spectra of (a) Fe-TPyP and (b) Fe-TPyP/ PMAA
Figure 4.9 shows the UV-Vis DR spectra of Fe-TPyP/PMAA with different
amounts of Fe-TPyP loading. The Soret band at around 417 nm shows an increase of
the intensity with the increase in the amount of Fe-TPyP loading.
Figure 4.10 shows the ESR spectra
of Fe-TPyP and Fe-TPyP/PMAA
(containing 50 and 100 µmol Fe-TPyP). The signal at g = 2.00056 or g = 2.0011 for
Fe-TPyP/PMAA with Fe-TPyP = 100 and 50 ȝmol respectively, are attributed to
high-spin Fe(III)-porphyrin. From this spectra, is shown that there shift toward a
higher g-value confirming the interaction between Fe-TPyP and the polymer matrix.
With increasing amount of Fe-TPyP loading from 50–100 ȝmol, intensity of the
signal at g ~ 2.00 was also found to be correspondingly higher.
73
K-M / a. u
Fe-TPyP=100 ȝmol
Fe-TPyP=50 ȝmol
Fe-TPyP=25 ȝmol
Fe-TPyP=10 ȝmol
Fe-TPyP=5 ȝmol
400
500
600
700
800
Wavelength / nm
Figure 4.9
UV-Vis DR spectra of Fe-TPyP/PMAA with various of amount of
Fe-TPyP loading
74
Intensity / a. u
Fe-TPyP
Fe-TPyP = 100ȝmol
Fe-TPyP = 50ȝmol
100
200
300
400
500
B / mT
Figure 4.10
ESR spectra of Fe-TPyP and Fe-TPyP/PMAA (containing 50 and
100 µmol Fe-TPyP)
Furthermore, in order to determine the binding ability of the Fe-TpyP
complex in the polymer support, the intensity of the spectra was measured. Tong et
al. [45] have also used this technique to evaluate the binding abilities of the polymer
to histamine. Measurement of the luminescence intensities of the polymer support
(PSSS-Po) in the absence and in the presence of quencher (azulene) has been shown
to confirm the occurrence of quenching of the support by the quencher [65].
75
The luminescence emission spectra of the PMAA, Fe-TPyP and FeTPyP/PMAA are presented in Figure 4.11. As can be seen in this figure, the PMAA
and Fe-TPyP exhibit the emission bands at 574 nm and 556 nm, respectively. More
significantly, the quenching effect of the Fe-TPyP luminescence caused a decrease of
the intensity of the band at around 572 nm.
Figure 4.12 show the luminescence emission spectrum of Fe-TPyP/PMAA
with different amount of Fe-TPyP loading. All the spectra exhibit bands at around
572 nm and two additional bands at range 650 – 750 nm. It can be seen that the
luminescence intensity of Fe-TPyP/PMAA at 572 nm and 650-750 nm decreases
with increasing amount of Fe-TPyP loading.
The efficiency of the energy transferred from PMAA to Fe-TPyP (Ȥ) was
calculated using Equation 4.1 and the experimental data. For example, under the
experimental condition (amount of Fe-TPyP loading = 100 ȝmol), the value of Ȥ was
found to be 0.373 (I0 = 552 and I = 206, at Ȝ = 572 nm). This means that 37.3% of
the energy absorbed by PMAA is transferred to Fe-TPyP and this indicates that
PMAA can act as an efficient energy donor [65].
Intensity / a. u
574
572
(a)
(b)
556
(c)
400
500
600
700
800
Wavelength / nm
Figure 4.11
The luminescence emission spectra of (a) as-synthesized PMAA,
(b) Fe-TPyP/PMAA and (c) Fe-TPyP (Ȝex = 333 nm)
76
Fe-TPyP=0µmol
Intensity / a. u
Fe-TPyP=5µmol
Fe-TPyP=10µmol
Fe-TPyP=25µmol
Fe-TPyP=50µmol
Fe-TPyP=100µmol
400
500
600
700
800
Wavelength / nm
Figure 4.12
The luminescence emission spectra of as-synthesized PMAA and
Fe-TPyP/PMAA with different of amount of Fe-TPyP loading (Ȝex = 333 nm)
77
The quenching effect can be described by the Stern-Volmer kinetics equation
expressed as a dependence of the ratio of the luminescence intensities (I0/I) of
PMAA on the amount of the Fe-TPyP loading (Figure 4.13). It is shown that the
luminescence intensity of the luminescent Fe-TPyP/PMAA decreases when PMAA
bound with Fe-TPyP. The considerable static interaction between PMAA and
Fe-TPyP exists in all I0/I values. The results confirm that the Fe-TPyP on PMAA is
engaged in high-affinity binding.
3
= 0.0162x++1.1895
1.1895
y =y 0.0162x
2
R2R= =0.9431
0.9431
2.5
I0/I
I 0 /I
2
1.5
1
0.5
0
0
20
40
60
80
100
120
Amount of Fe-TPyP Loading / ȝmol
Amount of Fe-TPyP Loading / µmol
Figure 4.13
The Stern-Volmer kinetics: the dependence of the ratio of the
luminescence intensities (I0/I) on the Fe-TPyP concentration
The
13
C CP/MAS NMR spectra of Fe-TPyP complexes, as-synthesized
PMAA and Fe-TPyP/PMAA are shown in Figure 4.14. The effects of encapsulation
are appreciable for the lineshape of the carboxyl carbon (-COOH) of PMAA. The
shift of the lineshape of the carboxyl carbon of PMAA to higher magnetic field may
be attributed to the formation of hydrogen bonding between unpaired electron of
–N= in Fe-TPyP and –COOH group of PMAA. To examine fully the lineshape of the
carboxyl carbon of PMAA in the Fe-TPyP/PMAA, we have shown the expansion of
the carboxyl region in Figure 4.14 and the assigment of the 13C the chemical shifts in
Table 4.2.
78
* Impurities
Relative Intensity / a. u
*
*
*
*
*
*
*
*
* *
*
*
*
*
*
*
(a)
*
(b)
*
(c)
*
(d)
C
CH2
COOH
*
*
200
CH3
*
(e)
*
150
100
50
0
Chemical shift / ppm
Figure 4.14
13
C CP/MAS spectra of Fe-TPyP/PMAA with various of amount of
Fe-TPyP loading (a) 100 ȝmol, (b) 50 ȝmol, (c) 25 ȝmol, (d) 5 ȝmol and
(e) as-synthesized PMAA
79
Table 4.2 : Assignment of chemical shifts of
13
C CP/MAS NMR spectra of
as-synthesized PMAA and Fe-TPyP/PMAA with various of amount of Fe-TPyP
loading
Chemical shift (ppm)
Sample
CH3
C
CH2
COOH
Polymethacrylicacid (PMAA)
16.8
43.4
60.8
173.6
Fe-TPyP/PMAA (Fe-TPyP= 5ȝmol)
17.1
44.2
61.3
172.9
Fe-TPyP/PMAA (Fe-TPyP= 25ȝmol)
16.0
43.1
60.7
175.3
Fe-TPyP/PMAA (Fe-TPyP= 50ȝmol)
15.3
42.9
60.0
175.9
Fe-TPyP/PMAA (Fe-TPyP=100ȝmol)
13.6
40.5
58.2
176.0
The elemental analyses of the Fe-TPyP/PMAA samples were performed by
means of AAS. Table 4.3 summarized the values obtained from AAS measurements
of the iron content in the polymer matrix. It is surprising that the values found are
below the expected values of the Fe loaded in the samples.
The difference is probably due to leaching of Fe-TPyP into solution during
the encapsulation procedure. However, the table clearly demonstrates the increase of
the iron content with increasing Fe-TPyP loading in the samples.
Table 4.3: Iron content (%Fe) of Fe-TPyP/PMAA with different amount of Fe-TPyP
loading determined by AAS
Sample
Fe (%)
Fe-TPyP/PMAA (Fe-TPyP= 100 ȝmol)
0.0185
Fe-TPyP/PMAA (Fe-TPyP= 50ȝmol)
0.0110
Fe-TPyP/PMAA (Fe-TPyP= 25 ȝmol)
0.0073
Fe-TPyP/PMAA (Fe-TPyP= 10 ȝmol)
0.0059
Fe-TPyP/PMAA (Fe-TPyP= 5 ȝmol)
0.0043
80
The thermal degradation behavior of as-synthesized PMAA, Fe-TPyP/PMAA
and Fe-TPyP complexes were studied in the range 50 – 900 °C. Figure 4.15 shows
two main stages of PMAA degradation with maximum decomposition rates at 240
and 380 °C. The first stage of decomposition is due to the weight loss of adsorbed
water and anhydride formation reaction.
In the second degradation stage, the polymer decomposes with the
elimination of CO and CO2 by way of abundant backbone scission and formation of
a small concentration of unsaturation. TGA results of Fe-TPyP show three weight
loss regions below 150 °C, 450-500 °C and 530-600 °C.
In first stage, endothermic weight losses were observed below 150 °C, which
can be reasonably assigned to the desorption of water. Further, the two significant
weight losses within 450-500 °C and 530-600 °C are due to the decomposition or
burning of iron-porphyrin.
100
90
80
70
Weight / %
60
50
(a)
40
30
(b)
20
(c)
10
0
300
600
900
Temperature / oC
Figure 4.15
TGA thermograms of (a) Fe-TPyP complexes, (b) Fe-TPyP/PMAA
and (c) as-synthesized polymethacrylic acid (PMAA)
81
The TGA profile of Fe-TPyP/PMAA show three stages of decomposition
within intervals 50–150 °C, 150–280 °C and 280– 450 °C. It can be seen from Figure
4.16 that the first peak on the curve of Fe-TPyP/PMAA represents evolution of water
molecules bound to Fe-TPyP and anhydride formation of uncomplexed carboxylate
groups of PMAA. The second peak on the curve is broad and likely represents
overlapping of two processes: the release of CO2 and CO of carboxylate groups of
PMAA and initial decomposition of porphyrin.
The shift of the second peak of Fe-TPyP/PMAA decomposition to a higher
temperature range in comparison with PMAA may be caused by dissociation of
hydrogen bonds between functional groups of PMAA with functional groups of
Fe-TPyP complex. The shift of the second stage of Fe-TPyP decomposition is not
higher than the temperature range of Fe-TPyP decomposition, obviosly because
amount of Fe-TPyP loading in the polymer matrix is very small. The third
degradation stage is similar to as-synthesized PMAA, where unsaturated products
and some CO2 and CO are released.
Table 4.3 shows the surface properties of PMAA-supported Fe-TPyP
catalysts determined from surface area analysis. A decrease in the surface area was
observed as the amount of iron loading onto the polymer increased up to 100 µmol,
which might be due to the blocking of pore of the support as well as due to the steric
hindrance [79].
Table 4.3 : Surface properties of PMAA-supported Fe-TPyP with different amount
of Fe-TPyP loading
Samples
Surface area (m2g-1)
PMAA
127
Fe-TPyP/PMAA (Fe-TPyP= 5 ȝmol)
112
Fe-TPyP/PMAA (Fe-TPyP= 10 ȝmol)
98
Fe-TPyP/PMAA (Fe-TPyP= 25 ȝmol)
64
Fe-TPyP/PMAA (Fe-TPyP= 50 ȝmol)
48
Fe-TPyP/PMAA (Fe-TPyP= 100 ȝmol)
23
82
CHAPTER 5
SINGLE-STEP SYNTHESIS OF PHENOL FROM BENZENE OVER
Fe-TPyP/Al-MCM-41 AND Fe-TPyP/PMAA CATALYSTS
5.1
Reaction Mechanism of Benzene Oxidation to Phenol
Oxidation of benzene to phenol represents a critical test for the reactivity of
transition metalloporphyrin in catalytic oxidations using hydrogen peroxide as
oxidant. It has been demonstrated that a least five products of the benzene oxidation
may be resulted (Scheme 5.1).
The reaction mechanism for the oxidation of aromatic compounds employing
transition metalloporphyrin has been previously studied [80]. The reaction path
proposed for the present study involves a first stage, where the interaction of ironporphyrin supported catalyst with hydrogen peroxide yields the P-Fe-OOH species,
via redox mechanism.
Iron porphyrin peroxide further converted to iron-oxo species (P-Fe(V)=O) as
shown in Scheme 5.2, which are similar to the hypervalent species of iron(V)-oxo
observed in cytochrome P-450. This iron-oxo species is active enough to insert its
“oxygen” atom into the C-H bond leading to hydroxylation product, therefore
displays oxo chemistry feature.
83
OH
OH
O
HO
•
+
OH
H2O
O
OH
OH
OH
OH
Scheme 5.1
The probable products of benzene oxidation (phenol, hydroquinone,
catechol, resorcinol and benzoquinone)
For the oxidation of benzene, the iron-oxo species attack the aromatic ring to
form the benzyl radical, and the so-called oxygen rebound mechanism to form the
phenol. For the formation of quinines, the benzyl radical is converted into the phenyl
radical by a second attack of iron-oxo species. From phenyl radical, hydroquinone
could be formed together with iron(III)-porphyrin.
5.2
The Single-Step Synthesis of Phenol from Benzene
The catalytic experiments were performed in a batch reactor with continuous
stirring in the liquid-phase at 70 °C. Benzene was used without further purification.
A typical oxidation procedure is as follows: 2 mL of benzene (22.5 mmol), 50 mg of
catalysts, and hydrogen peroxide (1 mL) were mixed together and stirred. The liquidphase reactor was a 50 mL two-necked round bottle flask equipped with a condenser.
84
For optimization of the catalysts, the catalytic activity of the various catalysts
was compared after of 1, 3, 5 and 20 hours of reaction. The activities were
characterized by the yield of phenol in the oxidation of benzene. To investigate the
effect of temperature, the reaction was repeated and carried out at ambient
temperature (30 oC), 70 oC and 100 oC. For the effect of solvent on catalytic activity,
the reaction was carried out in different solvent, namely, methanol and acetic acid
and solvent-free. The solid catalysts were separated from the mixture by
centrifugation.
H
-
OH
(Z)
O
FeIII.P
+
(E)
OH
OH
P.FeV
4b
O
5
OH
OH
P.FeIII
OH
OH
H
O
O
H
4a
1
H
(Z)
FeIII.P
O
+
(Z)
H2O
H
-
P.FeIII
O
O
OH
2
3
P.FeV
O
OH
Schema 5.2
Proposed reaction path for the oxidation of benzene
H
85
5.3
Analysis of Reaction Products
The resulting products were analyzed periodically using gas chromatography
(GC). Gas chromatograph-mass spectroscopy (GC-MS) and high performance liquid
chromatograph (HPLC) was also used to verify the resulting products. All the
products were analyzed using GC to determine the amount of product while the
components of the products were identified by using GC-MSD.
5.3.1
Gas Chromatography (GC)
A sample of the mixture to be separated is introduced into this gas stream just
before it encounters the stationary phase; the components are separated by elution
and detected as they emerge in the gas at the other end of the column. They are
distinguished by the different times which the take to pass through the column- the
reaction times [81]. The basic concept of such an instrument has remained
unchanged since the first one was built, although there has been much refinement
and an amazing improvement in performance. The main components are shown in
Figure 5.1.
Experimental procedure:
GC (Hewlett Packard 5890 GC Series II) was used to identify the reaction
product equipped with a flame ionization detector (FID) and a polar column
(carbowax). The oven temperature was programmed according to the conditions
tabulated in Table 5.1.
86
Figure 5.1
Block diagram of a gas chromatograph
Table 5.1 : GC-FID oven-programmed set up for identifying phenol
5.3.2
GC Parameter
Temperature / Time
Oven Temperature
50 oC
Initial Temperature
50 oC
Initial Time
5 min
Rate
10 oC/min
Final Temperature
200 oC
Hold Time
5 min
Gas Chromatography – Mass Spectrometry Analysis (GC-MS)
Mass spectrometers, in their simplest forms, are designed to perform three
basic functions. These are (1) to vaporize compounds of widely varying volatility,(2)
to produce ions form the neutral molecules in the gas phase, and (3) to separate ions
according to their mass-to-charge ratios (m/z), detect, and record them [82]. Any
device featuring electrical detection and having the ability to separate gaseous
positive to as a mass spectrometer, whereas a mass spectrograph is an instrument in
which the focused ion beams are recorded on photographic plate.
87
The purpose of the mass spectrometer part of a GC-MS system is to provide
some definite information about the compounds as they elute from the gas
chromatograph, in general terms, the GC-MS has to perform one of two tasks: either
identification of unknown compounds or the detection of a known compound that
may or may not be present. The mass spectrometer provides information necessary to
fulfill these functions.
The techniques of gas chromatography and mass spectrometry, both ideally
suited for the analysis of complex mixtures, share many common factors. The
principal requirement which dictates the method of coupling the gas chromatograph
to the mass spectrometer is the pressure at which the ion source must operate [83].
Experimental procedure:
GC-MS (Agilent 6890N-5973 Network Mass Selective Detector) is equipped
with HP-5MS column (30m x 0.251 mm x 0.25 µm), diffusion pump and turbo
molecular pump. Sample was analyzed on splitless method with helium (He) as the
carrier gas. 0.2 µL of those samples were injected to GC using 10 µL syringes at
initial temperature 60 oC without hold time, with rate 15 oC/min until 250 oC, and
hold 2 minutes.
5.3.3
High Performance Liquid Chromatography (HPLC)
High performance liquid chromatography (HPLC) is a technique that has
arisen from the application to liquid chromatography (LC) of theories and
instrumentation that were originally developed for gas chromatography (GC). It was
known from gas chromatographic theory that efficiency could be improved if the
particle size of the stationary phase materials used in LC could be reduced [84]. High
performance liquid chromatography arose gradually in the late as these high
efficiency materials were produced, and as improvements in instrumentation allowed
88
the full potential of these materials to be realized. As HPLC has developed, the
particle size of the stationary phase materials used in LC has become progressively
smaller.
The stationary phases used today are called micro particulate column packing
and are commonly uniform, porous silica particles, with spherical or irregular shape,
and nominal diameters of 10, 5 or 3 µm. In analytical HPLC the mobile phase is
normally pumped through the column at a flow rate of 1 – 5 cm3 min-1. The mobile
phase in HPLC may be water, organic solvents or buffers either on their own or
mixed with one another.
Experimental procedure:
The products were analyzed by HPLC (Perkin Elmer Series 200) using a
Water system equipped with two Series 200 LC Pump and a Series 200 UV.Vis
Detector. A methanol / water gradient, starting at 70 / 30 (v/v) and reaching 100%
methanol within 15 minutes was used for elution. The samples were prepared by
solubilization in methanol /water 70 / 30 (v/v). A 0.1 mL sample was collected over
the needle and injected into the HPLC equipment. Their UV-Vis spectra were
recorded and compared with authentic samples
The results of the experiments are reported in terms of total conversion, X
and the product selectivity, S, where % conversion and % selectivity are defined as
follows:
Conversion, X (%) =
Amount of benzene reacted
Amount of benzene input
Amount of phenol resulting
Selectivity, S, (%) =
Amount of total product
x 100%
x 100%
89
5.4
Results and Discussion
5.4.1
Catalytic Activity
The single-step synthesis of phenol from benzene over Fe-TPyP/Al-MCM-41
and Fe-TPyP/PMAA has been investigated. This single-step benzene oxidation with
hydrogen peroxide can be considered as a potential commercial alternative to the
broadly practiced three-step synthesis route involving cumene as an intermediate
[85]. However, phenol is oxidized more easily than benzene and thus, many byproducts like hydroquinone and benzoquinone may be obtained
In the present study, the main product of the liquid-phase oxidation of
benzene over the various catalysts is phenol and the by-product is hydroquinone. The
turnover number (TON), defined as the molar ratio of phenol to the loaded Fe for the
reaction with Fe-TPyP/PMAA, was higher than that of Fe-TPyP/Al-MCM-41 (Table
5.2). If the surface area of the catalysts is taken into consideration, the TON per
surface area for the reaction with Fe-TPyP/PMAA becomes much higher compared
to that of Fe-TPyP/Al-MCM-41. It strongly confirms that the direct oxidation of
benzene to phenol is efficiently catalyzed by Fe-TPyP/PMAA.
Table 5.2 : Catalytic activity of single-step synthesis of phenol from benzenea
a
Catalyst
Fe/
ȝmol
Surface area of
catalyst / m2 g-1
Phenol yield /
ȝmol
TON per
Fe
Fe-TPyP
Al-MCM-41
Fe-TPyP/Al-MCM-41
(Fe-TPyP =100ȝmol)
Fe-TPyP/PMAA
(Fe-TPyP = 100ȝmol)
Fe-TPyP/Al-MCM-41
(Fe-TPyP = 100ȝmol)b
Fe-TPyP/PMAA
(Fe-TPyP = 100ȝmol)b
0.38
813
383
0.18
10.45
17.87
47
0.020
48
40.23
2011
-
-
15.97
-
-
-
34.58
-
All reaction were carried out at 70 oC for 20 hours with benzene (2 mL), 30% H2O2
(1 mL), and catalyst (50mg) with vigorous stirring. bThe reaction was performed
after washing and drying of the catalyst until third times.
90
Figure 5.2 shows the activities of the iron-porphyrins supported on molecular
sieve Al-MCM-41 and PMAA as catalysts for the single-step synthesis of phenol
from benzene. Unexpectedly, the reaction system containing unsupported Fe-TPyP
catalyst (homogeneous system) is much less reactive than Fe-TPyP/Al-MCM-41 and
Fe-TPyP/PMAA systems.
50
Phenol Yield / ȝmol
45
40
35
30
25
20
15
10
5
0
Al-MCM-41
FeTPyP
FeTPyP/AlMCM-41
FeTPyP/PMAA
Catalysts
Figure 5.2
Effect of the different catalyst on the phenol yield for 20 hours
reaction
The higher activity of the later systems possibly arises from Fe-TPyP
coordination to the molecular sieve or polymer, which renders it more resistant to
oxidative self-destruction. From the results, it is evident that Fe-TPyP/PMAA
catalyst gives higher phenol yield than Fe-TPyP/Al-MCM-41. This may be due to the
different coordination modes of Fe-TPyP complexes when composite with molecular
sieve and polymethacrylic acid (PMAA).
91
5.4.2
The Selectivity of Products
Figure 5.3 shows the product selectivity of Fe-TPyP/Al-MCM-41 and
Fe-TPyP/PMAA catalysts toward the oxidation of benzene. GC and GC-MS analyses
indicate that phenol was the only product of the oxidation of benzene over
Fe-TPyP/Al-MCM-41 and other probable by-products, such as hydroquinone,
catechol and benzoquinone were not detected.
It is known that the Al-MCM-41 can act as alkylation catalyst due to the
presence of the Brönsted and Lewis acidity. Since cumene is an alkylation product of
benzene, was not produced in the reaction containing Fe-TPyP/Al-MCM-41
composite, it implies that the acid properties of Al-MCM-41 were suppressed by the
presence of Fe-TPyP. The lack of the acid properties may be attributed to the
interaction between the Brönsted acid site in Al-MCM-41 and the lone-pair electrons
of Fe-TPyP.
On the other hand, the product of Fe-TPyP/PMAA toward the production of
phenol was ca. 75%, since ca. 25% hydroquinone was also produced. The structure
of the supports seems to have a strong influence on the selectivity of the catalysts
toward phenol. The results suggest that the rigid ordered structure of Fe-TPyP/
Al-MCM-41 may have contributed to the very high selectivity for phenol.
120
Fe-TPyP-Al-MCM-41
Selectivity / %
100
Fe-TPyP-PMAA
80
60
40
20
0
Phenol
Hydroquinone
Reaction Products
Figure 5.3
The product selectivity of single-step synthesis of phenol in aqueous
hydrogen peroxide using Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA catalysts
92
The results (Figure 5.3) also suggest that the selective synthesis of phenol
from benzene requires Fe-TPyP in the limited pore channels of Al-MCM-41 to
suppress the formation of bulkier hydroquinone derivatives.
Figure 5.4 shows that the percentage (%) conversion of benzene to phenol at
70 °C over Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA. The results indicate that the
percentage conversion of benzene over Fe-TPyP/PMAA is higher than that of
Fe-TPyP/Al-MCM-41. In this case, the hydrophobic nature of Fe-TPyP/PMAA
provides for the higher activity and hence 100 % conversion of benzene to phenol
Conversion / %
120
100
80
60
40
20
0
Fe-TPyP/AlMCM-41-100
Fe-TPyP/AlMCM-41-50
Fe-TPyP/
PMAA-100
Fe-TPyP/
PMAA-50
Catalyst
Figure 5.4
The percentage conversion of benzene to phenol in aqueous hydrogen
peroxide using Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA catalysts
5.4.3
Regenerability of The Catalysts
The regenerability of the catalysts was studied at 70 °C for 3 cycles. The
Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA could be easily recovered from the
reaction products and regenerated by washing and drying in air. They were reused in
fresh reactant mixtures. The selectivity of encapsulated Fe-TPyP in Al-MCM-41 did
not change after three times of reusing and showed 100% activities (Table 5.3), but
the catalytic activities of Fe-TPyP/PMAA decreased to 75% after three cycles.
93
A decrease of the phenol yields between the initial reactions and the first
reusing is observed for benzene oxidation catalyzed by Fe-TPyP/Al-MCM41 and
Fe-TPyP/PMAA, giving an indication that the extraction procedure-using methanol
deactivates the catalysts through leaching of the Fe-TPyP complex into solution.
This was also observed for Fe-TPyP/PMAA, which presented a decrease in
its activity from the fresh reaction compared with the recycle. A decrease in the
activity of the catalyst from the first to the third recycle could be attributed to the
leaching or decomposition of Fe-TPyP complex under the present reaction condition.
The hydrogen peroxide as oxidant may have contributed to the leaching of the active
sites of the catalysts.
Table 5.3 : The catalytic activity of Fe-TPyP supported in Al-MCM-41 and
polymethacrylic acid (PMAA) during the recycling in single-step synthesis of phenol
from benzene
Benzene Oxidation
Number
of
Catalyst
Selectivity (%)
ȝmol)
Recycle
Fresh
Phenol Yield
17.87
100
1
15.97
100
2
16.32
100
3
15.66
100
40.23
75
1
34.58
70
2
32.00
75
3
31.70
75
Fresh
Fe-TPyP/Al-MCM-41-100
Fe-TPyP/PMAA-100
Although Fe-TPyP/PMAA showed higher activity compared to Fe-TPyP/
Al-MCM-41, the selectivity and the regenerability of Fe-TPyP/PMAA is not as good
as that of Fe-TPyP/Al-MCM-41. Based on the discussion, one considers that the
hydrophobic nature of Fe-TPyP/PMAA may account for the high catalytic activity,
while the ordered structure of Fe-TPyP/Al-MCM-41 provides for a high selectivity in
oxidation of benzene with aqueous hydrogen peroxide.
94
5.4.4
Optimization of Catalyst
Optimization of the catalyst activity of the supported Fe-TPyP/Al-MCM-41
and Fe-TPyP/PMAA catalyst was further explored by investigating the effect of
reaction time, solvent, the loading amount of Fe-TPyP and reaction temperature.
(a)
Effect of Reaction Time
The effect of reaction time on single-step synthesis of phenol from benzene
with hydrogen peroxide in the presence of various catalysts is shown in Figure 5.5. It
is seen that the step increase in the phenol yield occurs beginning at 1 hour reaction
time over both catalysts. After which, it can be observed that the phenol yield
increased almost linearly with the increase in the reaction time up to around
20 hours.
(b)
Effect of Solvent
Figure 5.6 shows the effect of different solvent on the phenol yield in the
presence Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA as catalysts at 70 °C for
20 hours of reaction time. The highest phenol yield was obtained when the reaction is
performed without solvent. With solvent, the activity of the catalysts may have been
hindered, due to leaching of the iron-porphyrin complexes into solution during the
reaction process.
For reaction that was carried out in a solvent, evidently, the more polar acetic
acid is better solvent than methanol for the synthesis of phenol. The yield of phenol
was found to increase with increasing polarity of the solvent.
95
45
Phenol Yield / ȝmol
40
35
30
25
20
15
Fe-TPyP-Al-MCM-41 (Fe-TPyP = 100 ȝmol)
Fe-TPyP-Al-MCM-41 (Fe-TPyP = 50 ȝmol)
Fe-TPyP-PMAA (Fe-TPyP = 100 ȝmol)
Fe-TPyP-PMAA (Fe-TPyP = 50 ȝmol)
10
5
0
0
5
10
15
20
25
Reaction Time / h
Figure 5.5
Effect of reaction time on the phenol yield in the single-step synthesis
of phenol from benzene over Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA catalysts
45
Fe-TPyP/Al-MCM-41
Phenol Yield / µmol
Phenol Yield / ȝmol
40
Fe-TPyP/PMAA
35
30
25
20
15
10
5
0
Solvent-Free
Acetic Acid
Methanol
Solvent
Solvent
Figure 5.6
Effect of different solvent on the phenol yield using Fe-TPyP/
Al-MCM-41 and Fe-TPyP/PMAA as catalysts at 70 °C
96
(c)
Effect of Loading Amount of Fe-TPyP
It can be seen in Figure 5.7 that samples (Fe-TPyP/Al-MCM-41 or
Fe-TPyP/PMAA) with the higher amount of Fe-TPyP loading give rise to higher
yields of phenol at 70 °C after 20 hours of reaction. The results show that the product
yield is greatly influenced and determined by the presence of Fe-TPyP as active sites.
Furthermore, it obvious that the amount of Fe-TPyP sites plays an important role in
the direct oxidation of benzene to phenol.
Phenol Yield / ȝmol
45
40
Fe-TPyP-Al-MCM-41
35
Fe-TPyP-PMAA
30
25
20
15
10
5
0
50
100
Amount of Fe-TPyP loading / ȝmol
Figure 5.7
Effect of amount of Fe-TPyP loading on the phenol yield in solvent-
free at 70 °C for 20 hours reaction time over Fe-TPyP/Al-MCM-41 and
Fe-TPyP/PMAA catalysts.
97
(d)
Effect of Reaction Temperature
The effect of temperature on phenol yields was studied at room temperature
and 70 °C over Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA as catalysts. The results
are presented in Figure 5.8.
Comparison of the results at room temperature and 70 °C illustrated that
higher phenol yield was obtained for the latter than the former due to higher activity
of hydrogen peroxide at room temperature. At a higher temperature of 100 °C over
both catalysts, the phenol yield was found to be much less, which is probably
because of coking. The higher temperature may have resulted in side reactions such
as alkylation and oligomerization. The side products could have poisoned the active
sites, blocked the pores and decreased the activity and selectivity of the catalysts.
Phenol Yield / ȝmol
45
40
Fe-TPyP/Al-MCM-41
35
Fe-TPyP/PMAA
30
25
20
15
10
5
0
30
R.T
70
100
o
Temperature / C
Figure 5.8
Effect of reaction temperature on phenol yield in solvent-free for
20 hours reaction time over Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA catalysts.
98
CHAPTER 6
CONCLUSION AND RECOMMENDATION
The encapsulation of bulky iron(III)-5,10,15,20-tetra-(4-pyridyl) porphyrin
(Fe-TPyP) complexes within the ordered structure of mesoporous molecular sieve
Al-MCM-41 (Fe-TPyP/Al-MCM-41) and polymethacrylic acid (Fe-TPyP/PMAA) as
inorganic and organic supports, respectively, were successfully achieved by
sequential synthesis of Fe-TPyP via treatment of FeCl3 with 5,10,15,20-tetra-(4pyridyl) porphyrin (TPyP) into the pores of Al-MCM-41 and polymerizing a
monomer methacrylic acid (MAA) with a cross-linker around the Fe-TPyP
complexes. The immobilized Fe-TPyP systems have demonstrated excellent activity
and selectivity for the single-step synthesis of phenol from benzene. The physical
properties of Fe-TPyP/Al-MCM-41 and Fe-TPyP/PMAA were investigated by
means of several spectroscopy characterization techniques.
The materials obtained were characterized by X-ray Diffraction (XRD),
Fourier Transform Infrared (FTIR), Ultraviolet Visible Diffuse Reflectance (UV-Vis
DR), Electron Spin Resonance (ESR), luminescence and
13
C CP/MAS NMR
spectroscopies, Thermogravimetric Analysis (TGA) and wet chemical analysis. The
powder XRD data confirmed that the ordered structure of mesoporous Al-MCM-41
remained intact after encapsulation process. Characterization of Fe-TPyP composites
with Al-MCM-41 and PMAA using FTIR, UV-Vis DR and ESR analysis confirmed
that the structure of Fe-TPyP in inorganic and polymer supports is similar with bare
Fe-TPyP. The three peaks in the range of 500–700 and at 462 nm in the UV-Vis DR
spectrum are observed in UV-Vis DR of Fe-TPyP/Al-MCM-41 which are typical of
99
high-spin Fe(III)-porphyrin and the axial electrostatic interaction between cationic
Fe-TPyP and anionic Al-MCM-41. The band at 589 nm in the spectrum of
Fe-TPyP/PMAA corresponds to the coordination of the Fe-TPyP OH-containing
PMAA.
The specific interaction of Fe-TPyP in Al-MCM-41 and/or PMAA was
studied by ESR,
13
C CP/MAS NMR and luminescence spectroscopies. The ESR
spectra of Fe-TPyP/PMAA and Fe-TPyP/Al-MCM-41 composites showed that there
is a shift towards a higher g-value confirming the interaction between Fe-TPyP and
the supports is occurred. By quenching of the luminescence spectra of
Fe-TPyP/PMAA with difference in the concentration of Fe-TPyP, it is proven that
there is interaction between Fe-TPyP and PMAA, presumably by the formation of
hydrogen bonding between Fe-TPyP and the polymer. Further support of the
interaction was obtained by
13
C CP/MAS NMR which shows that the peak of
carboxyl of PMAA is shifted to high magnetic field. The change in the position of
the carboxyl carbon may be attributed to the formation of hydrogen bonding between
unpaired electron of –N= bond in Fe-TPyP and –COOH group of PMAA.
Single-point BET surface area analysis was used to determine specific
surface area of the composites. It is revealed that surface area of Fe-TPyP/
Al-MCM-41 composites is decreased with an increase in the loading amount of
Fe-TPyP, suggesting the encapsulation of complex in the pores of Al-MCM-41 has
been achieved.
With mesoporous molecular sieve (Al-MCM-41) and the polymer (PMAA)
as supports, the immobilized iron-porphyrin system has demonstrated excellent
activity for the single-step synthesis of phenol from benzene under mild reaction
conditions. The effect of reaction time, solvent, amount of Fe-TPyP loading,
temperature and the performance of the recovered catalysts have been studied. The
immobilized iron-porphyrin in PMAA (Fe-TPyP/PMAA) gives a higher activity
compared with Fe-TPyP supported on Al-MCM-41 (Fe-TPyP/Al-MCM-41).
However, the product selectivity of Fe-TPyP/PMAA is not as good as that of
Fe-TPyP/Al-MCM-41.
One
considers
that
the
hydrophobic
nature
of
Fe-TPyP/PMAA may account for the high activity, and the ordered structure of
100
Fe-TPyP/Al-MCM-41 provides for the high selectivity in the single-step synthesis of
phenol from benzene in the present study.
In conclusion, the study presented in this thesis is sufficient to establish the
remarkable selectivity of Fe-TPyP/Al-MCM-41 as catalyst in single-step synthesis of
phenol from benzene. As a global guide for future actions, this work opens new
perspectives for the use of a more hydrophobic ordered structure materials containing
Fe-TPyP as a catalyst for synthesis of phenol from benzene.
101
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Breitmaier, E. and Bauer, G. 13C NMR Spectroscopy, A Working Manual with
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Ren, T., Yan, L., Zhang, X. and Suo, J. Selective Oxidation of Benzene to
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Nakagaki, S., Mangrich, A. S., Xavier, C-R. and Machado, A. M. Synthesis
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Tamayo, F.G., Casilas, J.L., and Esteban, A.M. Highly Selectivity FenorenImprinted Polymer with a Homogeneous Binding Site Distribution Prepared
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109
APPENDIX A
ULTRAVIOLET VISIBLE DIFFUSE REFLECTANCE (UV-Vis DR)
1.
UV-Vis diffuse reflectance spectroscopic data of Fe-TPyP/Al-MCM-41
samples with different amount of Fe-TPyP loading (see Chapter 3).
Samples
Characteristic bands (nm)
Fe-TPyP
424, 510, 585, 644
Fe-TPyP/Al-MCM-41 (Fe-TPyP = 5ȝmol)
424, 454, 521, 590, 644
Fe-TPyP/Al-MCM-41(Fe-TPyP = 10ȝmol)
421, 462, 519, 590, 644
Fe-TPyP/Al-MCM-41(Fe-TPyP = 25ȝmol)
416, 454, 520, 590, 644
Fe-TPyP/Al-MCM-41(Fe-TPyP = 50ȝmol)
421, 460, 518, 589,644
Fe-TPyP/Al-MCM-41(Fe-TPyP = 100ȝmol)
414, 462, 517, 589, 644
2.
UV-Vis diffuse reflectance spectroscopic data of Fe-TPyP/PMAA
samples with different amount of Fe-TPyP loading (see Chapter 4).
Samples
Characteristic bands (nm)
Fe-TPyP
424, 510, 585, 644
Fe-TPyP/PMAA(Fe-TPyP = 5ȝmol)
417, 515, 589, 644
Fe-TPyP/PMAA (Fe-TPyP = 10ȝmol)
418, 513, 588, 644
Fe-TPyP/PMAA (Fe-TPyP = 25ȝmol)
418, 512, 587, 644
Fe-Fe-TPyP/PMAA (Fe-TPyP = 50ȝmol)
418, 515, 590, 644
Fe-TPyP/PMAA (Fe-TPyP = 100ȝmol)
418, 517, 590, 644
110
APPENDIX B
LUMINESCENCE SPECTROSCOPY (LS)
1.
Luminescence intensity change of Fe-TPyP/PMAA with Fe-TPyP
binding.
Fe-TPyP (ȝmol)
I
I0/I
ȋ = 1 - I/I0 *
0
552
1
0
5
452
1.221
0.627
10
382
1.445
0.548
25
334
1.653
0.489
50
249
2.217
0.395
100
206
2.680
0.181
* I and I0 represent the luminescence intensity in the presence or absence of
Fe-TPyP. (I0 = 552)
2.
The Stern-Volmer kinetics: the dependences of the ratio of the
luminescence intensities (I0/I) on the Fe-TPyP concentration.
3
y = 0.0162x + 1.1895
y = 0.0162x + 1.1895
R2 = 0.9431
2
R = 0.9431
2.5
I0 /I
2
1.5
1
0.5
0
0
20
40
60
80
Amount of Fe-TPyP Loading / ȝmol
100
120
111
APPENDIX C
SCANNING ELECTRON MICROSCOPY (SEM)
1.
Scanning
electron micrographs of
magnifications scales show: (a) 5µm and (b) 2µm)
(a)
(b)
Fe-TPyP/Al-MCM-41
(2
112
3.
Scanning electron micrographs of (a) Fe-TPyPAl-MCM-41 (Fe-TPyP =
100 ȝmol) and (b) Fe-TPyP/Al-MCM-41 (Fe-TPyP = 50 ȝmol)
(a)
(b)
113
APPENDIX D
GAS CHROMATOGRAPHY (GC)
1.
Gas Chromatography Data of Authentic sample Calibration for phenol
No.
Concentration (mmol)
Area
1.
0.003
12277
2.
0.004
13310
3.
0.005
14641
4.
0.006
17625
5.
0.008
20817
6.
0.01
34017
7.
0.02
76414
8.
0.03
93879
9.
0.04
145490
10.
0.05
161522
11.
0.06
244752
12.
0.08
389370
13.
0.1
454572
14.
0.5
3063656
15.
1
5166445
114
Calibration Curve of Phenol Standard
1.2
Phenol Concentration / mmol
2.
1
y = 2E-07x + 0.0088
Ry2==2E-07x
0.9919 + 0.0088
2
R = 0.9919
0.8
0.6
0.4
0.2
0
0.E+00
0
2.E+06
2
4.E+06
4
AreaArea
(x 10-6)
6.E+06
6
115
5.766
Chromatograms of Substrates
Benzene
tR (min)
Methanol
Phenol
16.071
17.327
Hydrogen peroxide
tR (min)
24.387
4.688
3.
116
4.
Verification of phenol by GC technique
a.
Chromatograms of (a) phenol standard sample and (b) an example
reaction product from oxidation benzene with hydrogen peroxide at 70 oC for 3
hours using Fe-TPyP/Al-MCM-41.
Phenol
Methanol
(a)
Benzene
Methanol
Phenol
(b)
117
b.
GC Chromatograms of (a) phenol standard sample and (b) an example
reaction product from oxidation benzene with hydrogen peroxide at 70 oC for 3
hours using Fe-TPyP/PMAA.
Phenol
Methanol
(a)
Benzene
Methanol
Phenol
(b)
118
APPENDIX E
GAS CHROMATOGRAPHY-MASS SPECTROMETRY (GC-MS)
1. Total Ion Chromatograms of Benzene standard
Abundance
TIC: HD-14.D
1.8e+07
1.7e+07
1.6e+07
1.5e+07
1.4e+07
1.3e+07
1.2e+07
1.1e+07
1e+07
9000000
8000000
7000000
6000000
5000000
4000000
3000000
2000000
1000000
0
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Time-->
Abundance
Scan 85 (2.565 min): HD1.D
78
12000
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
52
1000
55
74
63
83
98
0
45
m/z-->
50
55
60
65
70
75
80
85
90
95
100
105
119
2. Total Ion Chromatograms of Phenol standard
Abundance
TIC: HD-8.D
7000000
6500000
6000000
5500000
5000000
4500000
4000000
3500000
3000000
2500000
2000000
1500000
1000000
500000
0
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Time-->
Abundance
Scan 587 (3.436 min): HD-12.D
94
350000
300000
OH
250000
200000
150000
66
100000
50000
50
55
50
55
62
74
79
45
m/z-->
60
65
70
75
80
104 108
90
0
85
90
95
100 105 110 115
120
3. Total Ion Chromatograms of Hydroquinone standard
Abundance
TIC: HD-5.D
3200000
3000000
2800000
2600000
2400000
2200000
2000000
1800000
1600000
1400000
1200000
1000000
800000
600000
400000
200000
0
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Time-->
Abundance
Scan 1097 (6.350 min): HD-5.D
110
750000
700000
650000
OH
600000
550000
500000
450000
400000
350000
300000
OH
250000
200000
81
150000
53
100000
50000
63
69
58
0
45
m/z-->
50
55
60
65
70
74
75
80
85
90
95
90
95 100105110115120125130135140
105
122
135
121
4.
Total Ion Chromatograms of Products using Fe-TPyP/Al-MCM-41 as
catalysts 70 oC for 3 hours.
Abundance
TIC: HD-12.D
1.7e+07
1.6e+07
1.5e+07
1.4e+07
1.3e+07
1.2e+07
1.1e+07
1e+07
9000000
8000000
7000000
6000000
5000000
4000000
3000000
2000000
1000000
0
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Time-->
Abundance
Scan 785 (4.567 min): HD-14.D
94
OH
3500
3000
2500
78
2000
1500
66
1000
51
500
55
63
69
104
74
0
45
m/z-->
50
55
60
65
70
75
80
85
90
95
100
105
110
122
5.
Total Ion Chromatograms of Products using Fe-TPyP/PMAA as
catalysts 70 oC for 3 hours.
Abundance
TIC: HD-13.D
1.8e+07
1.7e+07
1.6e+07
1.5e+07
1.4e+07
1.3e+07
1.2e+07
1.1e+07
1e+07
9000000
8000000
7000000
6000000
5000000
4000000
3000000
2000000
1000000
0
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Time-->
Abundance
Scan 591 (3.459 min): HD-13.D
94
220000
200000
OH
180000
160000
140000
120000
100000
80000
66
60000
40000
20000
50
55
50
55
62
74 78 82
0
45
m/z-->
60
65
70
75
80
105 110
85
90
95 100 105 110 115
123
6.
Mass
spectra
of
(a)
hydroquinone
standard
sample
and
(b)
hydroquinone from oxidation of benzene at 70 oC for 3 hours over Fe-TPyP/
PMAA.
Abundance
Scan 1097 (6.350 min): HD-5.D
110
750000
700000
650000
OH
600000
550000
500000
450000
400000
350000
300000
OH
250000
200000
81
150000
53
100000
50000
63
69
74
58
0
45
50
55
60
65
70
75
80
85
90
95
90
95 100105110115120125130135140
105
122
135
m/z-->
(a)
Abundance
Scan 1308 (7.556 min): HD-9.D
110
18000
17000
16000
15000
14000
13000
12000
11000
10000
9000
8000
7000
6000
81
5000
4000
3000
54
2000
1000
63
253
95
0
50 60 70 80 90 100110120130140150160170180190200210220230240250
m/z-->
(b)
124
APPENDIX F
HIGH PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC)
1.
HPLC chromatograms of (a) phenol standard sample and (b) phenol
10.59
Phenol
10.44
Response (mV)
2.99
from oxidation benzene at 70 oC for 3 hours using Fe-TPyP/Al-MCM-41.
Phenol
Methanol
Time (min)
2.88
Response (mV)
(a)
Methanol
Time (min)
(b)
125
2.
HPLC chromatograms of (a) the mixture between phenol and
hydroquinone standard samples and (b) phenol and hydroquinone from
10.44
Phenol
10.36
Response (mV)
2.85
oxidation benzene at 70 oC for 3 hours using Fe-TPyP/PMAA.
Phenol
Methanol
4.77
Hydroquinone
Time (min)
Methanol
4.61
3.05
Response (mV)
(a)
Hydroquinone
Time (min)
(b)
126
APPENDIX G
REACTION PATH FOR THE OXIDATION OF BENZENE TO PHENOL
1.
Reaction path
for
the oxidation
of
benzene
to
phenol
over
Fe-TPyP/Al-MCM-41
Step 1
P-Fe3+-Al-MCM-41 + H2O2
P-Fe4+(OH)-Al-MCM-41
P-Fe4+(OH)-Al-MCM-41 + H2O2
P-Fe4+(OOH)-Al-MCM-41 + H2O
P-Fe4+(OOH)-Al-MCM-41
P-Fe5+=O-Al-MCM-41 +
+ -OH
-
OH
Step 2
(Z)
OH
(Z)
5+
4+
P-Fe =O-Al-MCM-41 +
P-Fe -Al-MCM-41
OH
P-Fe3+-Al-MCM-41
+
and
OH
2P-Fe4+(OH)-Al-MCM-41 +
+
OH
2P-Fe3+-Al-MCM-4
1
127
2.
Reaction path for the oxidation of benzene to phenol over Fe-TPyP/
PMAA
Step 1
O
O
O
FeIII
H
+
H
FeIII
O
P
H
+
H+
P
H
O
+ O
H
O
-H2O
FeIII
FeV
+
R
H
P
P
Step 2
OH
FeV
2
H
FeIV
+
P
P
FeIII
.
O
H
+ HO
P
and
O
FeIII
H
+ HO
P
IV
Fe
P
FeIII
P
OH
P
+
HO
OH
.
FeV
OH
128
APPENDIX H
LIST OF PUBLICATIONS
1.
Nur, H., Hamid, H., Endud, S. and Ramli, Z., “Iron-porphyrin Encapsulated
in poly(methacrylic acid) and Mesoporous Al-MCM-41 as Catalysts in the
Oxidation of Benzene to Phenol”, Materials Chemistry and Physics, In Press,
2005.
2.
Hamid, H., Endud, S., Nur, H. and Ramli, Z., “Synthesis and Characterization
of Poly(methacrylic acid) (PMAA)-Iron(III) Porphyrin Hybrid Catalyst for
Oxidation of Benzene to Phenol”, Paper presented at Symposium on Science
and Mathematics 2004 (SSM 2004), Universiti Teknologi Malaysia, 2004.
3.
Hamid, H., Endud, S., Nur, H. and Ramli, Z., “Comparative Study of ironporphyrin supported on Mesoporous Al-MCM-41 and Poly(methacrylic acid)
(PMAA) : Characterization and their Catalytic Activities”, Poster presented at
Annual Fundamental Science Seminar 2004 (AFSS 2004), Ibnu Sina
Institute,Universiti Teknologi Malaysia, 2004.
4.
Hamid, H., Endud, S., Nur, H. and Ramli, Z., “Encapsulation of IronPorphyrin within Ordered Mesoporous Al-MCM-41: Synthesis,
Characterization and Catalytic Activity”, Report for Post-Graduate First
Assessment, Pusat Pengajian Siswazah, Universiti Teknologi Malaysia, 2004.