SYNTHESIS AND CHARACTERIZATION OF SULPHATED AlMCM-41 AND
ITS CATALYTIC ACTIVITY IN DIBENZOYLATION OF BIPHENYL WITH
BENZOYL CHLORIDE
NG ENG POH
UNIVERSITI TEKNOLOGI MALAYSIA
PSZ 19:16 (Pind. 1/97)
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESISυ
JUDUL:
SYNTHESIS AND CHARACTERIZATION OF SULPHATED
AlMCM-41
AND
ITS
CATALYTIC
ACTIVITY
IN
DIBENZOYLATION
OF
BIPHENYL
WITH
BENZOYL
CHLORIDE
SESI PENGAJIAN: 2004/2005
Saya:
NG ENG POH
(HURUF BESAR)
mengaku membenarkan thesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan
Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:
1.
2.
3.
4.
Tesis ini hakmilik Universiti Teknologi Malaysia.
Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan
pengajian sahaja.
Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi.
**Sila tandakan (√ )
√
SULIT
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia seperti yang termaktub di
dalam AKTA RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah
ditentukan oleh organisasi/badan di mana
penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
(TANDATANGAN PENULIS)
Alamat Tetap:
8, Taman Salad,
09600 Lunas, Kedah.
Tarikh:
CATATAN:
15 March 2006
(TANDATANGAN PENYELIA)
PROF. DR. HALIMATON HAMDAN
(Nama Penyelia)
Tarikh:
15 March 2006
* Potong yang tidak berkenaan
** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak
berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini
perlu dikelaskan sebagai SULIT atau TERHAD
υ Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana
secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan
penyelidikan, atau Laporan Projek Sarjana Muda (PSM).
“I hereby declare that I have read this thesis and in my opinion this
thesis is sufficient in terms of scope and quality for the award of the
degree of Master of Science (Chemistry)”.
Signature
: _______________________
Name of Supervisor
: Prof. Dr. Halimaton Hamdan
Date
:
15 March 2006
BAHAGIAN A – PENGESAHAN KERJASAMA*
Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui
kerjasama antara __________________ dengan _________________________
Disahkan oleh:
Tandatangan : ……………………………
Nama
: ……………………………
Jawatan
: ……………………………
Tarikh : ……………
(Cop Rasmi)
*Jika penyediaan tesis / projek melibatkan kerjasama.
BAHAGIAN B – Untuk Kegunaan Pejabat Sekolah Pengajian Siswazah
Tesis ini telah diperiksa dan di akui oleh:
Nama dan Alamat
Pemeriksa Luar
:
Prof. Madya Dr. Misni Bin Misran
Fakulti Sains
Universiti Malaya
50603 Kuala Lumpur
Nama dan Alamat
Pemeriksa Dalam I
:
Prof. Madya Dr. Salasiah Binti Endud
Fakulti Sains
UTM, Skudai
Disahkan oleh Penolong Pendaftar di SPS :
Tandatangan : ………………………………………
Nama
GANESAN
A/L ANDIMUTHU …
:…
…………………………………
Tarikh : ……………..
SYNTHESIS AND CHARACTERIZATION OF SULPHATED AlMCM-41 AND
ITS CATALYTIC ACTIVITY IN DIBENZOYLATION OF BIPHENYL WITH
BENZOYL CHLORIDE
NG ENG POH
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Science (Chemistry)
Faculty of Science
Universiti Teknologi Malaysia
MARCH 2006
I declare that this thesis entitled “SYNTHESIS AND CHARACTERIZATION OF
SULPHATED
AlMCM-41
AND
ITS
CATALYTIC
ACTIVITY
IN
DIBENZOYLATION OF BIPHENYL WITH BENZOYL CHLORIDE” is the result
of my own research except as cited in the references. The thesis has not been
accepted for any degree and is not concurrently submitted in candidature of any other
degree.
Signature
:
Name
:
Ng Eng Poh
Date
:
15 March 2006
iii
For the Lord God Almighty,
My beloved family
And
My best friends
iv
ACKNOWLEDGEMENT
To God be all the glory! Halleluyah! All praise, glory and thanks give to
Almighty God for His amazing grace and merciful that supported and led me
throughout the whole process of completing this research.
I would like to take this opportunity to express my appreciation to my
beloved supervisor, Prof. Dr. Halimaton bt. Hamdan who introduced me to the field
of mesomorphous materials. Her guidance, help, experience, advice and support
throughout this research is greatly appreciated. Heartfelt thanks also to my all
beloved lecturers especially, Dr. Hadi Nur who had given me worthy advices,
valuable suggestions and constructive discussions during conducting this research.
Special thanks also go to Mr. Lim Kheng Wei for helping me to carry out the
27
Al MAS NMR measurements. My special thanks also go to all the colleagues of
Zeolite and Porous Materials Group (ZPMG) for their help and support throughout
my project. I would like to extend my appreciation to the laboratory assistant, Pn.
Mek Zum, En. Azmi, Pn. Mariam and the other laboratory assistants for the help
offered to me. Last but not least, I would like to thank my parents and my friends
especially Daniel Lim for their support and caring.
v
PREFACE
This thesis is the result of my work carried out in the Department of Chemistry,
Universiti Teknologi Malaysia between Jun 2002 to September 2004 under the
supervision of Prof. Dr. Halimaton Handan. Part of my work described in this thesis
has been reported in the following publications:
1. Ng Eng Poh, Hadi Nur, Mohd Nazlan Mohd Muhid and Halimaton Hamdan,
(2005). “Sulphated AlMCM-41: Mesoporous Solid Brönsted Acid Catalyst
for Dibenzoylation of Biphenyl”, Catalysis Today (Accepted).
2. Ng Eng Poh and Halimaton Hamdan, (2005). “Structural Properties and
Surface Acidity Characterization of Sulphated AlMCM-41”, Poster
Presentation in International Science Congress (ISC), Putra World Trade
Centre, Kuala Lumpur Malaysia.
vi
ABSTRACT
Benzoylation of biphenyl with benzoyl chloride is an important acylation
reaction, producing monosubstituted product, 4-phenyl benzophenone (4-PBP) and
disubstituted product, 4, 4’- dibenzoylbiphenyl (4, 4’-DBBP). 4, 4’-DBBP is a
monomer used as a component in emitting layer in polymer light emitting (PLED)
devices. The objective of this study is to synthesize and characterize a highly active
sulphated AlMCM-41 acid catalyst by enhancing its acidity through sulphation.
Firstly, the AlMCM-41 with various SiO2/Al2O3 ratios was prepared by direct
synthesis, followed by conversion to H-AlMCM-41 via ion exchange of NaAlMCM41 with ammonium nitrate. Finally, sulphated AlMCM-41 was prepared by
impregnation of sulphuric acid in toluene. The sulphated MCM-41 materials possess
high surface area (>500 m2/g) and large quantities of Brönsted acid sites after
characterizing with surface analyzer and pyridine infrared spectroscopy.
27
Al MAS
NMR indicates the presence of octahedrally coordinated extra-framework sulphated
aluminiums (EFAL) and aluminium sulphate. The Hammett indicators show that the
acid strength of the sulphated AlMCM-41 materials was stronger than sulphuric acid
and H-AlMCM-41 because of sulphate groups attached to aluminium atom in
sulphated AlMCM-41. The results of comparative study on the dibenzoylation of
biphenyl
reaction
indicate
that
only
sulphated
AlMCM-41
gives
both
monosubstituted 4-PBP and disubstituted 4, 4’-DBBP with the highest activity
compared to sulphuric acid, H-AlMCM-41 and sulphated amorphous silica.
vii
ABSTRAK
Benzoilasi bifenil dengan benzoil klorida merupakan tindak balas pengasilan
yang penting, menghasilkan hasil penukargantian mono, 4-fenil benzofenon (4-PBP)
dan hasil penukargantian dwi, 4, 4’- dibenzoilbifenil (4, 4’-DBBP). 4, 4’-DBBP
merupakan monomer yang digunakan dalam lapisan pemancaran dalam peranti
pemancar cahaya polimer (PLED). Objektif kajian ini adalah untuk meningkatkan
keasidan mangkin yang digunakan dalam tindak balas pemangkinan dwibenzoilasi
bifenil melalui modifikasi H-AlMCM-41. AlMCM-41 dengan nisbah SiO2/Al2O3
disintesiskan melalui kaedah sintesis secara langsung, diikuti dengan menukarkannya
kepada bentuk H-AlMCM-41 melalui penukaran ion menggunakan ammonium
nitrat. Akhirnya, AlMCM-41 tersulfat disediakan melalui kaedah pengisitepuan
dengan asid sulfurik dalam toluena. Mangkin AlMCM-41 tersulfat mempunyai luas
permukaan yang tinggi (>500 m2/g) dan kuantiti tapak asid Brönsted yang banyak
selepas dicirikan dengan penganalisis permukaan dan spektroskopi inframerah
piridina.
27
Al MAS NMR menunjukkan kehadiran Al tersulfat luar bingkaian yang
berkoordinatan oktahedra dan aluminium sulfat. Penunjuk Hammett menunjukkan
bahan MCM-41 tersulfat mempunyai kekuatan asid yang lebih tinggi daripada asid
sulfurik dan H-AlMCM-41. Keputusan tindak balas dwibenzoilasi bifenil
menunjukkan bahawa hanya AlMCM-41 tersulfat memberikan hasil penukargantian
mono (4-PBP) dan dwi (4, 4’-DBBP) dengan keaktifan tertinggi berbanding dengan
asid sulfurik, H-AlMCM-41 dan silika amorfus tersulfat.
viii
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
TITLE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
PREFACE
v
ABSTRACT
vi
ABSTRAK
vii
TABLE OF CONTENT
viiii
LIST OF TABLES
ix
LIST OF FIGURES
xii
LIST OF SYMBOLS AND ABBREVIATIONS
xv
LIST OF APPENDICES
1
2
xviii
INTRODUCTION
1.1 Research Background and Problem Statement
1
1.2 Objectives of Research
4
1.3 Research Strategies
4
1.4 Scope of the Research
4
LITERATURE REVIEW
2.1 The Importance of Solid Catalyst
6
2.2 Solid catalysts - Introduction to M41S family
7
ix
2.3 Generation of Active Sites in AlMCM-41
Mesoporous Materials
3
10
2.4 Generation of acid sites via sulphation
12
2.5 Friedel-Crafts Reactions and Solid Catalysts
14
EXPERIMENTAL
3.1 Starting Materials
15
3.2 Preparation of AlMCM-41
15
3.3 Preparation of Protonated MCM-41
16
(H-AlMCM-41)
3.4 Synthesis of Sulphated AlMCM-41
17
3.5 Characterization of MCM-41 Materials
17
3.5.1 X-ray Powder Diffraction (XRD)
17
3.5.2 Fourier Transform Infrared Spectroscopy
(FTIR)
18
3.5.3 Solid State Magic Angle Spinning
Nuclear Magnetic Resonance (MAS
NMR) Spectroscopy
19
3.5.4 Thermogravimetric and Differential
Thermal Analysis (TG-DTA)
21
3.5.5 Nitrogen Adsorption-Desorption
Isotherm Analysis
22
3.5.6 Fourier Transform Infrared
Spectroscopy of Pyridine Adsorption
3.5.7 Hammett Acidity Analysis
3.6 Dibenzoylation of Biphenyl Reaction over
23
26
26
Sulphated AlMCM-41
3.6.1 Dibenzoylation of Biphenyl Reaction
over Various Types of Catalysts
28
3.6.2 Synthesis of 4-PBP as authentic sample
28
3.6.3 Synthesis of 4, 4’-DBBP as authentic
Sample
29
x
3.6.4 Calibration Curve for Authentic Sample
4
29
RESULTS AND DISCUSSION
4.1 X-Ray Diffraction Analysis
32
4.2 Infrared Spectroscopy of AlMCM-41
Molecular Sieves
36
4.3 Nitrogen Adsorption Measurement
38
4.4 Thermal Analysis
40
27
4.5 Solid State Al MAS NMR
29
43
4.6 Solid State Si MAS NMR
47
4.7 Acidity Measurements
49
4.7.1 Pyridine-FTIR Spectroscopy
49
4.7.2 Hammett indication Analysis
53
4.8 Catalytic testing: Dibenzoylation of
Biphenyl
55
4.8.1 Effect of Catalyst
55
4.8.2 Effect of SiO2/Al2O3 ratio
58
4.8.3 Reaction Temperature
59
4.8.4 Effect of Catalyst Loading
60
4.8.5 Effect of Benzoyl Chloride : Biphenyl
Mole Ratio
4.9 Mechanism
62
63
4.10 Mass balance of Dibenzoylation of Biphenyl
with Benzoyl Chloride
4.11 Proposed Structure
5
66
68
CONCLUSIONS
5.1 Conclusions
69
REFERENCES
71
APPENDICES
77
xi
LIST OF TABLES
NO. TABLE
TITLE
PAGES
2.1
Comparison of the various phases of catalysts.
7
3.1
Amount of NaAlO2 added in preparing AlMCM-41.
16
3.2
The organic compounds used as Hammett Indicators.
26
3.3
GC-FID oven-programmed setup for identifying 4, 4’-DBBP.
27
3.4
GC-MSD oven-programmed setup for identifying 4, 4’-DBBP.
28
4.1
XRD data of various MCM-41 samples.
33
4.2
The textural properties of various protonated and sulphated
39
MCM-41 samples obtained form calculation and surface
analyzer.
4.3
Peak areas of octahedral aluminium (Aloct) and tetrahedral
45
aluminium (Altet) from 27Al MAS NMR spectra
4.4
Peak areas of octahedral aluminium species in aluminium
45
sulphate (AlAl2(SO4)3) and sulphated AlMCM-41 (AlSulphated
AlMCM-41)
from 27Al MAS NMR spectra.
4.5
Peak areas of silicon species in SCAL-4
48
4.6
Pyridine FTIR data of protonated and sulphated MCM-41
52
materials.
4.7
The results of acid strength of catalysts using Hammett
54
indicators.
4.8
Benzoylation and dibenzoylation of biphenyl with benzoyl
57
chloride over various types of catalysts at 180 oC for 24 h.
4.9
Amount of Brönsted acid active sites in SCAL-4 with different
61
loading and and its effect towards conversion of biphenyl.
4.10
Theoretical mass balance
67
4.11
Experimental mass balance
67
xii
LIST OF FIGURES
NO. FIGURE
1.1
TITLE
Two proposed reaction routes: (Route1) direct and (Route 2)
PAGES
3
consecutive synthesis of the dibenzoylation of biphenyl using
sulphated AlMCM-41 mesoporous materials and benzoyl chloride.
1.2
Flow diagram of research strategies.
5
2.1
Illustration of hexagonal honeycomb structure of mesoporous
9
MCM-41 with 2 nm to 10 nm pore size.
2.2
Formation of MCM-41 materials. (a) Coagulation of surfactants
9
process, (b) Combination of organic and inorganic materials, (c)
MCM-41.
2.3
Framework of (a) SiMCM-41 and (b) AlMCM-41.
10
2.4
Generation of Brönsted acid sites.
11
2.5
Generation of Lewis acid sites.
12
2.6
Benzoylation of an aromatic compound using aluminium
13
trichloride as catalyst, leading to a stable Lewis complex.
2.7
Friedel-Crafts acylation showing a typical starting materials,
14
products and waste mass balance.
3.1
Range of 29Si chemical shifts of Qn in solid silicate.
21
3.2
Proposed mechanism of interaction between pyridine molecules
24
with (a) Brönsted and (b) Lewis acid sites in MCM-41 molecular
sieves.
3.3
Adsorption and desorption of pyridine apparatus for acidity study.
25
3.4
Quantitative calibration plot of biphenyl.
30
3.5
Quantitative calibration plot of 4-PBP.
30
3.6
Quantitative calibration plot of 4, 4’-DBBP.
31
xiii
4.1
X-ray diffractogram patterns of uncalcined mesoporous MCM-41
34
molecular sieves. (a) UNCAL-1, (b) UNCAL-2, (c) UNCAL-3
and (d) UNCAL-4.
4.2
X-ray diffractogram patterns of mesoporous MCM-41 materials
34
after calcinations at 550 oC for 10 h. (a) CAL-1, (b) CAL-2, (c)
CAL-3 and (d) CAL-4.
4.3
X-ray diffractogram patterns of protonated MCM-41 materials
35
o
after ion exchange with NH4NO3 and calcination at 500 C (a)
HCAL-1, (b) HCAL-2, (c) HCAL-3 and (d) HCAL-4.
4.4
X-ray diffractogram patterns of sulphated MCM-41 materials (a)
35
SCAL-1, (b) SCAL-2, (c) SCAL-3 and (d) SCAL-4.
4.5
FTIR spectra of uncalcined mesoporous MCM-41 molecular
37
sieves.
4.6
FTIR spectra of calcined mesoporous MCM-41 molecular sieves.
37
4.7
FTIR spectra of sulphated mesoporous MCM-41 molecular sieves.
38
4.8
Modification of surface of MCM-41 through sulphation leads to
39
shrinkage of pore diameter.
4.9
Thermogravimetric analysis of uncalcined MCM-41 sample
40
(UNCAL-2) in nitrogen gas with 20 oC/min heating rate.
4.10
Thermogravimetric analysis of uncalcined MCM-41 samples with
41
various ratio of SiO2/Al2O3.
4.11
Thermograms of a series of protonated MCM-41 molecular sieves.
42
4.12
Thermogravimetric curves of sulphated AlMCM-41 materials.
43
4.13
27
44
Al NMR spectra of protonated MCM-41 molecular sieves (a)
HCAL-4, (b) HCAL-3, (c) HCAL-2 and (d) HCAL-1.
4.14
27
Al NMR spectra of sulphated MCM-41 molecular sieves (a)
44
SCAL-4, (b) SCAL-3, (c) SCAL-2 and (d) SCAL-1.
4.15
29
Si NMR spectrum of sulphated MCM-41 molecular sieves
48
(SCAL-4).
4.16
The possible silicon species and Brönsted acid sites in sulphated
49
AlMCM-41.
4.17
The pyridine-FTIR spectra of purely siliceous sulphated MCM-41
(SCAL-1) at (a) room temperature, (b) 150 oC, (c) 250 oC and (d)
50
xiv
350 oC.
4.18
The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-2) at
o
o
51
o
(a) room temperature, (b) 150 C, (c) 250 C and (d) 350 C .
4.19
The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-3) at
51
(a) room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC .
4.20
The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-4) at
52
(a) room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC .
4.21
FTIR spectra of silanol groups of MCM-41 materials at 250 oC (a)
53
before treatment (HCAL-1) and (b) after treatment (SCAL-1) of
sulphuric acid.
4.22
Dibenzoylation of biphenyl catalyzed by various types of catalysts
57
4.23
Conversion of biphenyl over various ratio of SiO2/Al2O3 within 24
58
h.
4.24
Yield of 4, 4’-DBBP over various ratio of SiO2/Al2O3 within 24 h.
59
4.25
Temperature effect towards dibenzoylation of biphenyl over
60
SCAL-4.
4.26
Effect of catalyst loading towards dibenzoylation of biphenyl over
61
SCAL-4.
4.27
Effect of Biphenyl : Benzoyl Chloride molar ratio towards
62
dibenzoylation of biphenyl over SCAL-4.
4.28
Mechanism of how the electron density affects BP and 4-PBP in
63
attacking benzoylium ion.
4.29
Formation of 4-phenyl benzophenone (4-PBP) via electrophilic
64
substitution.
4.30
Mechanism of production of 4, 4’-dibenzoyl biphenyl (4, 4’-
65
DBBP).
4.31
Stoichiometrical chemical equation of dibenzoylation of biphenyl
66
reaction.
4.32
Hydrolysis of benzoyl chloride as side reaction in production of
68
benzoic acid and benzoic anhydrice.
4.33
Scheme proposed for the sulphated AlMCM-41 materials showing
possible Brönsted acid sites.
68
xv
LIST OF SYMBOL AND ABBREVIATIONS
MCM-41
-
Mobile Crystalline Material-41
RHA
-
Rice husk ash
Py
-
Pyridine
i.e.
-
Id est (that is)
BET
-
Brunauer-Emmett-Teller
GC
-
Gas chromatography
Å
-
Angstrom (10-10 meters)
kV
-
Kilovolts
α
-
Alpha
β
-
Beta
PDPV
-
Poly (4, 4’-diphenylene diphenylvinylene)
LED
-
Light emitting devices
IUPAC
-
International Union of Pure Applied Chemistry
LCT
-
Liquid-crystal templating
n
-
Diffraction order from n = 1, 2, 3, ….
d
-
Distance
2D
-
Two dimensions
λ
-
Lambda
θ
-
Theta
δ
-
Delta
FTIR
-
Fourier transform infrared
NMR
-
Nuclear magnetic resonance
MAS
-
Magic angle spinning
CP
-
Cross polarization
EFAL
-
Extra-framework aluminium
ppm
-
Part per million
xvi
%
-
Percent
~
-
Approximately
TG/DTA
-
Thermogravimetric and Differential Thermal Analysis
TGA
-
Thermogravimetric Analysis
DTA
-
Differential Thermal Analysis
Ho
-
Hammett acidity function
µL
-
Microlitre
MS
-
Mass spectrometry
GC-MS
-
Gas
chromatography
combined
with
spectrometry
4-PBP
-
4-Phenyl benzophenone
4, 4’-DBBP
-
4, 4’-dibenzoylbiphenyl
CTABr
-
Cetyltrimethylammonium bromide
NH4OH
-
Ammonium hydroxide
min
-
Minute
o
-
Celsius
h
-
Hour
wt%
-
Weight percent
g
-
Gram
mg
-
milligram
SiO2/Al2O3
-
Silica over alumina ratio
mol
-
Mole
mmol
-
Millimole
m.p.
-
Melting point
mA
-
Milliampere
o
-
Degree
cm-1
-
Per centimeter
UNCAL-1
-
Uncalcined MCM-41 with SiO2/Al2O3 ratio ∞
UNCAL-2
-
Uncalcined AlMCM-41 with SiO2/Al2O3 ratio 60
UNCAL-3
-
Uncalcined AlMCM-41 with SiO2/Al2O3 ratio 30
UNCAL-4
-
Uncalcined AlMCM-41 with SiO2/Al2O3 ratio 15
CAL-1
-
Calcined MCM-41 with SiO2/Al2O3 ratio ∞
CAL-2
-
Calcined AlMCM-41 with SiO2/Al2O3 ratio 60
C
mass
xvii
CAL-3
-
Calcined AlMCM-41 with SiO2/Al2O3 ratio 30
CAL-4
-
Calcined AlMCM-41 with SiO2/Al2O3 ratio 15
HCAL-1
-
Protonated MCM-41 with SiO2/Al2O3 ratio ∞
HCAL-2
-
Protonated AlMCM-41 with SiO2/Al2O3 ratio 60
HCAL-3
-
Protonated AlMCM-41 with SiO2/Al2O3 ratio 30
HCAL-4
-
Protonated AlMCM-41 with SiO2/Al2O3 ratio 15
SCAL-1
-
Sulphated MCM-41 with SiO2/Al2O3 ratio ∞
SCAL-2
-
Sulphated AlMCM-41 with SiO2/Al2O3 ratio 60
SCAL-3
-
Sulphated AlMCM-41 with SiO2/Al2O3 ratio 30
SCAL-4
-
Sulphated AlMCM-41 with SiO2/Al2O3 ratio 15
MHz
-
Megahertz
µs
-
Microsecond
TMS
-
Tetramethyl silane
BJH
-
Barrett, Joyner, Halenda
mbar
-
millibar
kPa
-
Kilopascal
m/z
-
Mass over charge
ao
-
Unit cell parameters
t
-
Crystallite size
Wd
-
Pore diameter
bd
-
Pore wall thickness
xviii
LIST OF APPENDICES
APPENDICES
A
TITLE
PAGES
Calculation of the amount of pyridine adsorbed on the sample in
77
the acidity study of sulphated AlMCM-41 samples.
B
Infrared spectrum of 4-phenyl benzophenone (4-PBP).
78
C
Mass spectrum of 4-phenyl benzophenone (4-PBP).
79
D
Infrared spectrum of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP).
80
E
Mass spectrum of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP).
81
F
Calculation of % conversion and % selectivity.
82
G
The pyridine-FTIR spectra of HCAL-1 at (a) room temperature,
83
o
o
o
(b) 150 C, (c) 250 C and (d) 350 C.
H
The pyridine-FTIR spectra of HCAL-2 at (a) room temperature,
84
(b) 150 oC, (c) 250 oC and (d) 350 oC.
I
The pyridine-FTIR spectra of HCAL-3 at (a) room temperature,
85
(b) 150 oC, (c) 250 oC and (d) 350 oC.
J
The pyridine-FTIR spectra of HCAL-4 at (a) room temperature,
o
o
86
o
(b) 150 C, (c) 250 C and (d) 350 C.
K
Chromatogram of reactants at 0 h.
87
L
Chromatogram of reactants and products.
88
M
Data obtained from GC-FID Chromatograms (Friedel-Crafts
89
dibenzoylation of biphenyl with benzoyl chloride over SCAL-4).
N
Mass balance of dibenzoylation of biphenyl with benzoyl
90
chloride (Experimental)
O
Mass balance of dibenzoylation of biphenyl with benzoyl
chloride (Theoretical)
98
1
CHAPTER 1
INTRODUCTION
1.1
Research Background and Problem Statement
Catalyst is defined as a substance that increases the rate of reaction without
being appreciably consumed in the process [1]. Catalyst increases the reaction rate by
offering other route of reaction with lower activation energy of the reaction system.
There are many chemical reactions which need this substance in order to enhance the
reaction rate. The presence of this substance is essential not only for enhancing
reaction rate but also decreasing energy consumption and minimizing the waste
production.
Today, catalysts play a vital role in the chemical industries, with a total
contribution of ~20% of world GNP [2]. Apart from that, there are approximately
80% of the industrial reactions such as acylation, oxidation, hydrogenation,
epoxidation etc. use catalysts. Among the reactions, Friedel-Crafts acylation
(benzoylation) reaction is of interest in industries due to the importance of preparing
aromatic ketones as intermediate in the dyes [3], pharmaceutical and fragrance [4]
industries. An example of benzoylation reaction which has been studied is the
benzoylation of biphenyl with benzoyl chloride [5-8]. More attention has been
centered on it because of its applications. The monosubstituted product, 4benzoylbiphenyl or 4-phenyl benzophenone (4-PBP) is used in the synthesis of
antifungal bifonazole agent [7]. The 4-PBP is also an intermediate in the synthesis of
fructone, an apple scent used in fragrant, detergents [9] and photo initiator [7] whereas
the disubstituted product, 4, 4’- dibenzoylbiphenyl (4, 4’-DBBP) is used as a
1
2
monomer in producing poly (4, 4’-diphenylene diphenylvinylene) or PDPV, an
attractive
polymer
for
electroluminescence
because
it
has
very
high
photoluminescence efficiency in solid state along with good solubility in common
organic solvents [10]. As a result, it is used as an emitting layer in polymer light
emitting (PLED) [11].
Liquid phase Friedel-Crafts reactions traditionally have been catalyzed by
strong Brönsted acids such as CF3SO3H, FSO3H, H2SO4 and HF and by soluble Lewis
acids such as TiCl4, AlCl3 and FeCl3 [12]. These acids are very strong in terms of
their catalytic activity. Unfortunately, some of the homogeneous catalysts such as
TiCl4, AlCl3 and FeCl3 are highly sensitive to moisture, corrosive and
environmentally unfriendly [13]. In industrial processes, the reaction brings another
disadvantage to this system where it has a difficulty in product purification due to
production of large amount of side products [14]. Therefore, a demand for searching
an alternative is a need to overcome this problem.
Recently, the use of solid acid catalysts such as zeolites [3, 4, 7] and
mesoporous materials [15, 16] has been reported for the acylation reaction. Zeolites
and mesoporous materials are known for their shape selective properties and they
have been used widely in a variety of acid and base catalyzed shape selective
reactions. In addition, these materials are easy to separate from the product,
environmentally unfriendly, small amount of hazardous corrosive wastes, high
catalyst reusability, high thermostability, safer and easier to handle [14, 17].
Current research on the production of 4, 4’-DBBP via homogeneous and
heterogeneous systems is still facing difficulties. For example, Walczak et al. [15]
were only able to prepare 4-PBP in 74% of yield by treatment of benzoyl chloride
with AlCl3 in chloroform at room temperature, followed by addition of biphenyl into
refluxing solution, Equation 1.1. Another researchers, viz. Han et al. [7] synthesized
94.2 % yield of 4-PBP by stirring benzoyl chloride with biphenyl and AlCl3 in the
presence of nitrobenzene at 120 oC, Equation 1.2.
2
3
Benzoyl chloride + AlCl3
+ Biphenyl
Reflux in CHCl3 at 25 oC
Benzoyl chloride + Biphenyl
+ AlCl3
4-PBP
Reflux in PhNO2 at 120 oC
(94.2%)
4-PBP
(74%)
(Equation 1.1)
(Equation 1.2)
Recently, the first attempt to synthesize 4, 4’-DBBP using H-AlMCM-41 as
heterogeneous catalyst with 100% selectivity was reported, however with very low
conversion (0.05%) [5]. According to the researchers, these unsatisfactory results
might be due to low amount of Brönsted and Lewis acid sites as well as its acid
strength. In addition, the reaction condition such as effect of temperature, solvent used,
reactants and catalyst loaded also contribute to these results. In view from the above,
it is of importance to (i) develop a new catalyst or modify the existing catalyst in
order to enhance the amount and the strength of acidity of the materials and (ii)
improve reaction condition for the selective synthesis of 4, 4’-DBBP. By taking the
actions suggested, it is expected that the activity of the catalyst will be improved.
Figure 1.3 shows two possible routes to drive the reaction to obtain targeted product 4,
4’-DBBP either via direct or consecutive route.
Biphenyl
+
Route 1
(Direct)
O
2
C
Benzoylium ion
+
MCM-41
materials
Route 2
(Consecutive)
O
O
4, 4'-dibenzoyl biphenyl
(4, 4'-DBBP)
Targeted product
O
4-Phenyl benzohenone
(4-PBP)
Figure 1.1: Two proposed reaction routes: Route1 (direct) and Route 2 (consecutive)
synthesis of the dibenzoylation of biphenyl using sulphated AlMCM-41
mesoporous materials and benzoyl chloride.
3
4
1.2
Objectives of Research
The objectives of the research are:
1. To synthesize and characterize a highly active sulphated AlMCM-41
heterogeneous acid catalyst.
2. To relate the acidity to the structural characteristic of the catalyst.
3. To study the catalytic properties of the developed catalyst in
dibenzoylation of biphenyl reaction (model reaction).
4. To study the effect of reaction parameters on the production of 4, 4’DBBP.
1.3
Research Strategies
The flow diagram shown in Figure 1.2 describes about research strategies.
Generally the studies involve synthesis, modification, catalytic testing and
optimization. Characterizations are carried out by various techniques as listed. The
catalytic activity was tested in a model reaction – dibenzoylation of biphenyl reaction.
The modification, characterization and catalytic activity testing processes were
repeated until a suitable catalyst was discovered.
1.4
Scope of Research
The work reported in this study focuses on the synthesis of sulphated
AlMCM-41 with various of SiO2/Al2O3 ratio using amorphous rice husk ash as silica
source and sodium aluminate as aluminium source. MCM-41’s template namely
cetyltrimethyl ammonium bromide (CTABr) was used as structure directing agent.
The modification was followed by conversion to H-AlMCM-41 via ion exchange of
NaAlMCM-41 with ammonium nitrate solution followed by calcination and lastly
impregnated with sulphuric acid in order to obtain sulphated AlMCM-41.
4
5
Characterization of each sample was carried out using Fourier Transform
Infared (FTIR) spectrometer to study the molecular bondings while the crystalinity
and crystallite size of the samples were analyzed by means of X-ray Diffraction
analysis (XRD). Furthermore, characterization of the samples was also conducted
using 29Si and 27Al Magic Angle Spinning NMR (MAS NMR) spectrometers to study
the silicon and aluminum environments in the structure whereas the textural properties such
as specific surface area, pore volume, pore diameter and pore wall thickness was measured by
using nitrogen gas adsorption-desorption analysis. The thermal stability and volatile
matter in the MCM-41 samples were determined by utilizing thermogravimetry and
differential thermal analysis. The acid strength and the type of acid sites were measured
using Hammett indicators and Fourier Transform Infrared spectroscopy (FTIR) using
pyridine as the probe base molecule.
The final part in this study is to test the catalytic capability of sulphated
AlMCM-41 towards Friedel-craft dibenzoylation of biphenyl with benzoyl chloride as
the benzoylating agents. The reaction was performed in a batch reactor and the
products were separated and analyzed quantitatively by gas chromatography (GC) and
the identification of products were carried out using gas chromatography with mass
spectrometry detector (GC-MSD).
5
6
No
Synthesis of
MCM-41 materials
Characterization
Catalytic testing
Modification and
improvement
MCM-41 materials are characterized to
Dibenzoylation of biphenyl, a
The properties of catalytic
determine their:
model reaction was carried out
system will be improved in
using direct synthesis
™Crystallinity - XRD
to test the activity of the
terms of
™Modification of MCM-41
™Textural properties (specific surface
catalysts.
™Acid strength
materials
area and pore volume) - N2 adsorption-
™Amount of acid site
desorption isotherm
™Specific surface area
™Synthesize
various
catalysts
SiO2/Al2O3
in
ratio
Satisfy
Yes
Finish
™Functional groups - FTIR
™Acidity (type, density and strength) -
Pyridine-FTIR, Hammett indicator
™Thermal stability, volatile matter -
TG-DTA
™Aluminum environment in the
structure - 27Al MAS NMR
™Silicon environment in the structure 29
Si MAS NMR
Figure 1.2: Flow digram of research strategies.
6
7
CHAPTER 2
LITERATURE REVIEW
2.1
The importance of solid catalyst
Catalysis has had a major impact on chemicals and fuels production,
environmental protection and remediation, processing of consumer products and
advanced materials manufacturing. A survey of British agency Frost and Sullivan
revealed that the catalyst European market had reached to USD 3.7 billion turnover in
2000 with the 4 % of average increment per year and it illustrates that the critical role
of this field in the fuel and chemical industry [18].
Homogeneous catalyst is referred as the catalyst that exists in the same phase
with the reactants whereas heterogenous catalyst is a catalyst which has different
phase with the reactants. Catalyst can be used either in gaseous, liquid or solid form.
Usually, heterogeneous catalyst is more favorable in application because it is easy to
isolate from the reaction mixture. Only a few heterogeneous catalysts in gaseous form
are used commercially because of difficulty in handling and safety factors. However,
the industries nowadays prefer to use solid form heterogeneous catalyst compared
with liquid form homogeneous catalyst due to high corrosion of vessels caused by
liquid form catalyst, difficulty in handling, leaking and spillage problems. Table 2.1
depicts the advantages and disadvantages of 3 phases of catalysts.
7
8
Table 2.1: Comparison of the various phases of catalysts.
Type(s)
Advantage(s)
• High activity towards reaction
Gas
due to kinetic factor.
Liquid
• High activity towards reaction
due to kinetic factor.
Solid
• Safer to use.
Disadvantage(s)
•
Leaking problem.
•
Difficulties in handling.
•
Possible explosion hazard.
•
Corrosive to vessels.
•
Difficulties in separation.
•
Leaking and spillage problems.
•
Difficulties in handling.
•
Corrosive to vessels.
•
Difficult to contain high active
• High activity towards reaction
component loading (dosage) to
further improve strength and
due to high surface area.
impact.
• Convenient to handle.
• No leaking and spillage.
•
Difficult to modify.
• Easy to use and separate.
•
Leaching problem.
Therefore, from Table 2.1 it is clear that among all types of catalysts, solid catalysts
have many advantages and currently are of interest.
2.2
Solid catalysts - Introduction to M41S family
Usually, a solid consisting of nanometer-sized cavities or pores has a high
surface area. International Union of Pure Applied Chemistry (IUPAC) classifies pore
sizes into three categories. Pores larger than about 50 nm in diameter are termed
macropores while those less than about 2 nm are termed micropores whereas pores of
intermediate size (2 nm < x < 50 nm) are classified as mesopores.
Microporous zeolites are widely used as acid catalysts nowadays. Acid sites
are generated by introducing metals such as aluminium [3, 4, 16] into the framework.
8
9
However, the zeolites with micropores still face many problems because they often
suffer from diffusion limitation when applied to the chemical synthesis involving
bulky molecules. Hence, the development of molecular sieves with pore diameter in
the mesoporous range has been increasing in demand for its use in acid catalyzed
reactions, particularly for the synthesis of large molecules for producing chemicals
[19]. One significant step forward came with the determination of the structure of
zeolite β [20, 21] which has three-dimensional channels larger than most microporous
zeolites and exhibits catalytic performances competitive with those widely used as
catalysts on an industrial scale such as Y-type and ZSM-5 zeolites. Another
significant step forward has come more recently with the discovery of the mesoporous
M41S family in 1992 [22], which offer many opportunities over microporous
materials by being more accessible to reactants.
In 1992, Mobil researchers reported that a family of aluminosilicates (termed
M41S) with pores larger than 2 nm could be synthesized in an ordered packing
through “liquid-crystal templating” (LCT) mechanism shown in Figure 2.1 [23].
Firstly, the surfactant aggregates to form rod-like micelles. Next, the silicate anions
will migrate and undergo polymerization, resulting in the formation of MCM-41
structure.
(a)
(b)
(c)
Fig. 2.1: Formation of MCM-41 materials. (a) Aggregation of surfactants process,
(b) Combination of organic and inorganic materials, (c) MCM-41 [26].
9
10
Of particular interest is MCM-41, which has hexagonally-packed cylindrical
pore channels containing surface areas greater than 1200 m2/g and uniform pore sizes
that can be tailored from 2 to 10 nm in diameter available, making it attractive
heterogeneous catalysts, catalyst supports, and nanocomposite host materials for a
wide range of novel applications, Figure 2.2 [22, 24]. A study of mesoporous MCM41 materials however, is of interest to chemists nowadays. Since the introduction of
MCM-41 with its unique characteristics, these materials have important uses in
chemistry disciplines [25].
Figure 2.2: Illustration of hexagonal honeycomb structure of mesoporous MCM-41
with 2 nm to 10 nm pore size.
Purely siliceous MCM-41 generally does not have catalytic ability because of
the absence of the Al as active sites. Therefore, in order to obtain acidic mesoporous
catalysts which are suitable for the synthesis of large hydrocarbons, a modification of
their acid sites is necessary. In recent years, many efforts have been devoted towards
the study of incorporating numerous kinds of metal or nonmetal compounds in MCM41 in order to enhance both the acid sites and strengths. For example, many
researchers reported that by incorporating trivalent metals such as Al or Ga in the
MCM-41, the Lewis and Brönsted acid characters can be generated and improved [9,
27-30]. On the other hand, the introduction of many metals other than Al and Ga, i.e.
10
11
In, Fe, Ti, Zr etc. is another promising ways to generate acid character in MCM-41
mesoporous sieves [12, 29, 31-33].
2.3
Generation of active sites in AlMCM-41 mesoporous materials
Purely siliceous MCM-41 mesoporous materials generally are neutral in term
of charge because of the +4 charge of Si in the SiO4 unit of the framework is
electronically neutralized by the four –1 charges from the oxygen atoms. It is shown
in Figure 2.3 (a). As a result, purely siliceous MCM-41 mesoporous materials do not
exhibit acidity due to neutral charge and have no heterocation such as Al in the
framework. However, the charge of framework of purely siliceous mesoporous
materials is no longer neutral when lattice Si4+ cations are replaced by lattice foreign
cation such as Al3+ cation. This phenomenon creates negatively charged framework of
the mesoporous materials as illustrated in Figure 2.3 (b).
0
O
(a)
Si
4+
Si
O
O
O
O
Al
O
O
Si
Si
O
Si
OO
OO
OO
O
O
O
O
-1
O
(b)
0
O
O
-1
O
3+
Si
O
O
O
O
Si
Al
OO
OO
O
Si
OO
O
Figure 2.3: Framework of (a) SiMCM-41 and (b) AlMCM-41.
Typically, AlMCM-41 materials are synthesized in the sodium form.
Therefore, it is a need to convert the Na+ form to H+ form in order to generate the
11
12
Brönsted acid sites as shown in Figure 2.4. It can readily be accomplished by ion
exchanging Na+ with NH4+ followed by thermal decomposition of the NH4+ into
proton and ammonia [5].
O
O
Si
Na
O
Si
Al
OO
O
O
Na O
Al
OO
OO
O
NH4+ exchange
O NH4 O
O
Si
Si
Al
OO
O
O NH4 O
OO
Al
OO
O
> 300 oC - NH3
Brönsted acid sites
H
O
O
Si
O
H
O
Si
Al
OO
O
OO
O
Al
OO
O
Figure 2.4: Generation of Brönsted acid sites.
The Lewis acid sites in aluminosilicate mesoporous materials are originated
from extraframework Al species (EFAL) present in the form of Al3+, AlO+, Al(OH)2+,
or charged AlxOyn+ clusters within the materials [36]. EFAL species is the Al species
that locates outside of the framework. There are two possible explanations about the
generation of Lewis acid sites. The first approach was proposed by Lercher et al. [37]
using infrared studies, stating that Lewis acidity is due to framework tricoordinated
aluminium formed upon dehydroxylation as demonstrated in Figure 2.5 (a). The
second explaination postulated by MAS NMR spectroscopy [38], which shows that
12
13
the presence of Lewis acid sites is associated with both octahedral and tetrahedral
extra framework Al (EFAL) species, created by dehydroxylation of the hydrogen
forms of aluminosilicate meterials as illustrated in Figure 2.5 (b).
(a) Lewis acidity due to framework tricoordinated aluminium.
H
O
H
O
O
Si
OO
OO
O
O
Si
O
O
O
OO
Si
Al
Si
Al
OO
O
O
OO
OO
- H2O
Si
Al
Si
Al
O
O
O
O
O
OO
OO
(b) Lewis acidity associated with both octahedral and tetrahedral EFAL.
H
O
O
Si
O
H
O
Si
Al
OO
O
OO
OO
- H2O
Si
Al
OO
O
O
O
O
O
Si
O
O
Si
Al
OO
AlO+ O
OO
O
Si
OO
O
Figure 2.5: Generation of Lewis acid sites:
2.4
Generation of acid sites via sulphation
Another method of modification and improvement of acid sites in MCM-41 is
via sulphation whereby it is a method of introducing sulphate group onto the MCM41. Sulphation has received much attention recently [33-35]. Chen et al. [35] first
reported the details of the synthesis and characterization of sulphuric acid
impregnated mesoporous materials for the synthesis of β-naphthyl methyl ether and
later M. Selvaraj et al. [33, 34] reported the synthesis, characterization of mesoporous
13
14
materials with different Si/Al ratios for synthesis of neroline. Usually sulphuric acid is
used as sulphating agent [33-35]. The sulphuric acid is impregnated in MCM-41
materials in aqueous solution followed by drying and readily be used in reaction.
Sulphation is simple and can generate Lewis acid site. Figure 2.6 illustrates the
scheme proposed by M. Selvaraj for the sulphate-containing AlMCM-41 material
showing possible Lewis acid sites. Impregnation by sulphuric acid enables the
generation of Lewis acid sites on the surface of AlMCM-41 due to the inductive effect
of the sulphate group and the aluminium ions is being non-framework. From this
point of view, sulphation provides a promising solution to the enhancement of acidity
and catalyzes Friedel-Crafts reaction that needs strong and large amount of acidity.
O
O BA O
O
Si
O
O
O
O
O
O
O
Si
O
LA
S
S
O
Al
O
O
2-
Si
O
O
O
Al
O LA O
O
Si
O
Figure 2.6: Scheme proposed for the sulphated AlMCM-41 material showing
possible
Lewis acid sites (LA) after sulpathating AlMCM-41 containing Brönsted
acid site (BA).
2.5
Friedel-Crafts reactions and solid catalysts
Friedel-Crafts reaction is an important synthesis techniques in organic
chemistry. It is widely used not only in research but also in chemical production
industries. One of the reactions called acylation reaction is of interest due to the
importance of preparing aromatic ketones as intermediate in the dyes [3],
pharmaceutical and fragrance [4] industries.
14
15
Liquid phase Friedel-Crafts reactions traditionally have been catalyzed by
strong Brönsted acids such as CF3SO3H, FSO3H, H2SO4 and HF and by soluble Lewis
acids such as TiCl4, AlCl3 and FeCl3 [12]. These acids have many important
advantages. They are very active and readily available. Apart from that, they are
cheap. Unfortunately, homogeneous catalysts such as TiCl4, AlCl3 and FeCl3 are
highly sensitive to moisture, corrosive and environmentally unfriendly [13]. They are
often too powerful acid, giving lower yield of desired product with low selectivity and
very significantly in the context of green chemistry, they may need to be used in
reagent quantities because of their ability to form complex Lewis base products. For
example, AlCl3 is used as a catalyst in a benzoylation reaction as shown in Figure 2.6.
COCl
R +
O
+ AlCl3
Solvent
AlCl3
R
Figure 2.6: Benzoylation of an aromatic compound using aluminium trichloride as
catalyst, leading to a stable Lewis complex.
When the reaction is complete, the only possible way to separate the AlCl3 is
by a destructive water quenching, resulting in emission of about 3 equivalents of HCl;
which need to be scrubbed off the gases leading to the production of 3 equivalents of
salt waste. Once the organic product has been recovered, aluminous water remains,
which must be disposed of. The overall process generates considerably more waste
than product, Figure 2.7 [2].
15
16
O
C
R
O
+ AlCl3 + RCCl
H2O
3 HCl + Al(OH)3
3 NaOH
3 NaCl
Substrates and reagents
……
1000 arbitrary weight units
Products
……
290 arbitrary weight units
Waste
……
710 arbitrary weight units
Figure 2.7: Friedel-Crafts acylation showing a typical starting materials, products and
waste mass balance.
In industrial processes, the reaction brings another disadvantage to this system
where it has a difficulty in product purification due to production of large amount of
side products [14]. Therefore, a demand for searching an alternative is a need to
overcome this problem. Recently, the use of solid acid catalysts such as zeolites [3, 4,
7] and mesoporous materials [12, 15, 16] has been reported for the Friedel-Crafts
reaction. Zeolites do seem to be a better alternative due to their shape selective
properties. In addition, these materials are easy to separate from the product,
environmentally friendly, small amount of hazardous corrosive wastes, high catalyst
reusability, high thermostability, safer and easier to handle [14, 17].
16
17
CHAPTER 3
EXPERIMENTAL
3.1
Starting Materials
Rice husk ash (RHA) containing 97% of SiO2 was used as the silica source for
MCM-41 while sodium aluminate (NaAlO2; Riedel-de-Haän®; 53 wt% Al2O3) was
used as aluminium source. Cetyltrimethylammonium bromide (CTABr) and acetic
acid (Merck, 25 wt%) were used as surfactant and organic acid, respectively. Sodium
hydroxide (NaOH; Merck; 99%) and ammonium hydroxide (NH4OH; Merck; 99%)
were used as alkali bases. Doubly distilled water was used as a medium. Ammonium
nitrate (Merck) was used as an ion-exchange agent to produce protonated mesoporous
materials whereas sulphuric acid (H2SO4; Merck; 95-97 v/v%) was the sulphating
agent. All reagents were of analytical purity. Benzoyl chloride and biphenyl were
used without further purification. The monosubstituted 4-phenyl benzophenone and
disubstituted 4, 4’-benzoyl biphenyl were synthesized via homogeneous FriedelCrafts reaction. These products were used as authentic samples.
3.2
Preparation of AlMCM-41
AlMCM-41 was prepared in the following way using published method [5]. In a
typical synthesis, sodium silicate was prepared by dissolving 6.13 g of RHA and 2.00
g of NaOH in 40.0 ml doubly distilled water at 80 oC for 2 h under stirring. The
resulting solution was designated as solution A. Another solution B was prepared by
mixing appropriate amount of NaAlO2 as shown in Table 3.1, 6.07 g of CTABr and
17
18
0.70 g of NH4OH 25 wt% in 35.0 ml of doubly distilled water, followed by stirring at
80 oC for 30 min until a clear solution was obtained. For both solutions, viz. A and B
were mixed together in a polypropylene bottle to give a gel with a mole ratio
composition of
6 SiO2 : CTABr : 1.5 Na2O : 0.15 (NH4)2O : 250 H2O
followed by vigorous stirring for 15 min. After stirring, the resulting gel was kept in
an air oven for crystallization at 100 oC for 24 h. The gel was then cooled to room
temperature and the pH of the gel was adjusted close to 10.2 by adding acetic acid 25
wt%. The subsequent 24 h heating and pH adjustment was repeated twice. The solid
product was filtered, washed, neutralized and dried overnight at 100 oC. The solid
sample was calcined at 550 oC in air for 10 h with a heating rate of 1 oC min-1 to
remove the trapped organic template. Calcined solid powders with SiO2/Al2O3 ratios
of ∞, 60, 30 and 15 were labelled as CAL-1, CAL-2, CAL-3 and CAL-4, respectively.
Table 3.1: Amount of NaAlO2 added in preparing AlMCM-41.
3.3
Sample
SiO2/Al2O3 ratios
NaAlO2 weight (g)
CAL-1
∞
0.00
CAL-2
60
0.19
CAL-3
30
0.38
CAL-4
15
0.76
Preparation of Protonated AlMCM-41 (H-AlMCM-41)
Calcined MCM-41 mesoporous materials (0.700 g) in Na+ form was put into a
50 ml of 0.2 M NH4NO3 solution and stirred at 60 oC for 6 h. The solid was filtered,
washed with deionized water and dried at 110 oC for 2 h. The ion exchange was
18
19
repeated three times. The solid powder was then calcined at 550 oC at the rate of 1 oC
min-1 for 5 h. The solid powders of H-AlMCM41 with SiO2/Al2O3 ratio of ∞, 60, 30
and 15 were labeled as HCAL-1, HCAL-2, HCAL-3 and HCAL-4, respectively.
3.4
Synthesis of Sulphated AlMCM-41
Sulphated AlMCM-41 samples were prepared the following way. 0.50 g of H-
AlMCM-41 was transferred to a round bottom flask containing 10 ml of toluene and
30 µL H2SO4 95-97 wt%. The mixture was stirred at 50 oC for 1 h and dried at 130 oC
for 12 h. The sulphated samples with SiO2/Al2O3 ratios of ∞, 60, 30 and 15 were
designated as SCAL-1, SCAL-2, SCAL-3 and SCAL-4, respectively.
3.5
Characterization of MCM-41 Materials
3.5.1 X-ray Powder Diffraction (XRD)
X-ray diffraction is a powerful method to define the crystallographic structure of
MCM-41 materials whereby no other means is feasible or even possible. Each of the
zeolite materials has their own specific pattern that can be used as references for the
determination of solid crystal phase and it is used as fingerprint for every zeolites.
This technique can identify the phase present in the sample and signify whether the
solid sample is amorphous or crystalline phase. Amorphous phases will produce no
diffraction peak at all and small particles will produce broad diffraction lines, whereas
a crystalline particle gives a sharp and strong diffraction lines. The degree of
crystallinity can also be determined by referring to peak intensity. The purity of solid
crystal can be measured by comparing the X-ray diffractogram pattern of sample with
X-ray diffractogram pattern of standard that can be attained from International Zeolite
Association (IZA). The presence or absence of some peaks of the diffractogram
19
20
indicates to the existence of other crystal phase or zeolite was contaminated with
other phases [39].
The crystallite size for MCM-41 can be easily determined by using the
Scherrer equation shown as follow [40].
t = 0.9 λ / (B cos θ)
(Equation 3.1)
where t is the average crystallite size in nm, B is the full width at half maximum of
diffraction peak, λ is the wavelength of X-ray and θ is the diffraction angle.
The unit cell parameters for MCM-41 can be determined by applying the
Equation 3.2.
a o = 2 d 100 / 3
(Equation 3.2)
where ao is the unit cell parameter in Å and d is the interplanar spacing
In this study, the MCM-41 mesoporous materials were characterized by means
of X-ray Powder Diffraction (XRD) using a Bruker Advance D8 using Siemens 5000
diffractometer with Cu Kα radiation (λ = 1.5418Å, 40 kV, 40 mA). First, the powder
samples were ground and spread on a sample holder. The samples were scanned in the
range from 2θ = 1.5 o – 10.0o with step size of 0.02o.
3.5.2
Fourier Transform Infrared Spectroscopy (FTIR)
FTIR is a very powerful analytical tool because it reveals information about
molecular vibrations that cause a change in the dipole of moment of molecules [41].
In zeolite chemistry, it is employed to study the aluminoslicate framework, hydroxyl
group and also foreign molecules adsorbed in the zeolites. Normally, FTIR provides
meaningful information in the mid-infrared region (1400-400 cm-1) which attributed to
the framework vibrations of zeolite which tetrahedral linked of SiO4 or AlO4. FTIR
20
21
also can be used to determine the hydroxyl group in zeolite. In air, the water vapour
will interact with the OH group in zeolites through hydrogen bonding and give a
broad band around 3700 – 3400 cm-1. For determination of OH group of zeolites, the
samples have to be heated at high temperature under vacuum to eliminate water
vapour trapped in zeolite framework [42].
Sulphate functional group shows several signals in IR spectra. The stretching
vibration of the S=O bond gives band at 1071 cm-1 while the absorption band at 1180
cm-1 is due to symmetric vibrations of Si–O–S bridges. Apart from that, sulphate
group also demonstrates a band at 888 cm-1 which is due to symmetric S–O stretching
vibrations. The SO2 deformation can also be detected in the region 580 cm-1 [43, 44].
In this research, infrared spectra were acquired by using a Perkin Elmer
Spectrum One FT-IR spectrometer with a 4 cm-1 resolution and 10 scans in the mid IR
region (400–4000 cm-1). KBr pellet method was used in which the solid samples were
finely pulverized with dry KBr in the ratio of 1:100 and the mixture was pressed in a
hydraulic press (5000 psi) to form a transparent pellet. The pellet was put in a sample
holder and the spectrum of the pellet was measured.
3.5.3 Solid State Magic Angle Spinning Nuclear Magnetic Resonance (MAS
NMR) Spectroscopy
In recent years, theory and practice have been developed for the NMR study of
solids. NMR is a powerful spectroscopic technique, which can be used for a number
of applications in various branches of chemistry. One of the applications of NMR is to
characterize zeolites and mesoporous materials concerning structure elucidation and
the short range ordering (local environment).
Usually, solid state NMR spectroscopy is performed using a number of special
techniques, including magic-angle spinning (MAS), cross polarization (CP), special
2D experiments and enhanced probe electronics in order to obtain a high resolution
21
22
spectrum [45]. Such techniques are needed because of the rapid, random motion
characteristic of liquids is strongly constrained, and low-abundance or low-sensitivity
nuclei causing line broadenings are not averaged.
There are many nuclei are used in zeolite chemistry such as 1H, 13C, 29Si, 27Al,
31
P and 19F. All these nuclei have spin and magnetic properties that can be utilized to
give chemical information.
27
Al and
29
Si MAS NMR are typically used to study the
structures of mesoporous materials such as AlMCM-41 because of their important
roles as framework elements where 27Al and 29Si are both magnetically active nuclei.
For 27Al NMR, the spectra with high signal-to-noise ratios are easily detected without
using CP technique like
29
Si MAS NMR due to the relatively high sensitivity of the
nucleus with a high natural abundance of 100% and the fast relaxation times. In a
sample of aluminosilicate, it was found that four coordination (tetrahedral)
aluminium, AlO4 had a chemical shift range from 55 – 80 ppm whereas six
coordination (octahedral) aluminium, AlO6 or termed extra-framework aluminium
(EFAL) occurred at ~0 ppm [46].
29
Si NMR spectra may be harder to obtain due to low sensitivity of the nucleus
with a low natural abundance of 4.7%. Hence, the so-called cross-polarization (CP)
technique is needed to overcome this problem. Generally, Qn notation is used to
present tetrahedral SiO4 where superscript n indicates the connectivity, i.e. the number
of other Q attached to the SiO4 tetrahedron. Figure 3.1 summarizes the
29
Si NMR
chemical shift regions [47]. From the table, the substitution of one or more Si atoms
by foreign atoms like Al in coordination sphere results in significant low-field shift,
i.e. give less negative δ value.
In this study,
27
Al MAS NMR spectra were recorded using a Bruker
Ultrashield 400 spectrometer under the following conditions;
27
Al at a frequency of
104.2 MHz with a spin-rate of 7 kHz, pulse length of 1.9 µs and a relaxation time
delay of 2 s. Each spectrum was obtained with 5000 scans. The chemical shifts of 27Al
were reported in relation to the tetramethyl silane (TMS). 29Si MAS NMR spectrum
was recorded at frequency of 79.5 MHz using 4 mm zirconia double bearing rotor
22
23
with a relaxation time delay of 600 s and spinning rate of 10 kHz with 45o pulses. The
chemical shifts were given in ppm from tetramethyl silane (TMS).
Figure 3.1: Range of 29Si chemical shifts of Qn in solid silicate
3.5.4
Thermogravimetric and Differential Thermal Analysis (TG-DTA)
TG-DTA is a technique whereby the weight of a sample and the phase
transitions or chemical reactions can be followed through observation of heat
absorbed or released over a period of time while its temperature is being raised
linearly. The theory of TG-DTA is simple. A sample is placed on the balance and the
furnace for sample heating is installed beneath the balance. The sample will be heated
and the electronic recording mechanism will plot a graph of weight and energy
adsorbed (endothermic) or released (exothermic) against time, termed thermogram.
TG-DTA can be used in studying:
™ Thermal degradation of a sample.
23
24
™ Chemical reaction resulting in changes of mass such as absorption,
adsorption, desorption.
™ Sample purity.
™ In some cases, it can be used for identification purposes [48].
In this experiment, the TG-DTA measurements were carried out on a Perkin
Elmer’s Pyris Diamond Thermogravimetric/Differential Thermal Analyzer under N2
atmosphere with a flow rate of 20 ml min-1 using ~ 10 mg of the sample. The sample
was heated in the temperature range 45 – 850 oC with a heating rate of 20 oC min-1.
3.5.5
Nitrogen Adsorption-Desorption Isotherm Analysis
Adsorption isotherm is a unique and useful technique in measuring surface
area and pore structure of a solid whereby no other means is feasible or even possible
[49]. The principal method of measuring total surface area of porous structures is by
physically adsorption of a particular molecular species from a gas (typically nitrogen)
onto the surface, maintained at a constant temperature (usually at liquid nitrogen
temperature 77K).
Nitrogen adsorption-desorption isotherm analysis is very useful because it
provides a lot of information related to textural properties of a sample. The surface
area and pore volume can be determined by using the Brunauer, Emmet and Teller
(BET) equation [50]. Meanwhile, the pore diameter, Wd of MCM-41 materials can be
calculated using Equation 3.3 [51].
Wd = C d100
⎛ ρV p
⎜
⎜ 1 + ρV
p
⎝
1
⎞2
⎟
⎟
⎠
(Equation 3.3)
in which C is a constant with having the value of 1.213, d100 is (100) interplanar
spacing, ρ is pore wall density with assumes to be 2.2 cm3/g for silica with amorphous
pore walls and Vp is the primary mesopore volume determined from adsorption
measurements. Apart from that, the wall thickness, bd of MCM-41 molecular sieves
can also be determined by applying Equation 3.4 [51].
24
25
bd = 2(3-1/2)d100 – Wd/1.050
(Equation 3.4)
where d100 is (100) interplanar spacing and Wd is pore diameter.
In this research, the specific surface area and pore volume of SCAL-1, SCAL2, SCAL-3 and SCAL-4 were analyzed by using the multi-point BET technique with a
Surface Area Analyzer instrument (Thermo Finnigan Qsurf Series). Approximately 10
mg of sample was used for every measurement. Prior to adsorption, the sample was
degassed for 30 min at 473 K under nitrogen gas flow condition. The samples were
then evacuated to 10-2 Torr and immersed in liquid nitrogen. The weight of sample
included sample holder was determined and the specific surface area and pore volume
measurements were measured.
3.5.6
Fourier Transform Infrared Spectroscopy of Pyridine Adsorption
Another application of FTIR spectroscopy is that it has been combined and
used in the characterization of surface acidity. For the most part, adsorption on
aluminosilicates involves acid-base interactions. Basic molecules such as pyridine is
chosen as the probe base due to its strong basicity property and its ability to interact
with a wide scale of acid strength as well as it can differentiate between the Brönsted
and Lewis sites. Pyridine adsorption monitored with FTIR gives acidity adsorptions in
the range of 1400 – 1700 cm-1 [20].
There are two types of acid sites present in MCM-41 materials, namely Lewis
and Brönsted acid sites. Brönsted acid site in MCM-41 materials occur when the
cations like H+ balances the anionic charge of framework. It can be defined as a
proton-donor-acidity [52]. This interaction usually gives a peak at ~3600 cm-1.
However, the peak disappears after introducing with pyridine and at the same time, a
new peak at ~1545 cm-1 will be observed which is due to pyridine bound to Brönsted
acid sites. The mechanism is depicted in Figure 3.3 (a). Lewis acid site arises at the
25
26
electron deficient sites that can accept a pair of electrons. In this case, pyridine with
nitrogen lone pair electrons acts as electron donor (nucleophile) while the MCM-41
framework acts as electron acceptor. Figure 3.3 (b) describes the mechanism on how a
pyridine molecule binds to Lewis acid sites where this interaction gives a peak at
~1455 cm-1.
H
N
H
Peak at ~3600 cm-1
O
Si
+
(a)
OO
N
Si
Al
OO
O O
Bronsted acid site
in AlMCM-41
Pyridine
Si
Si
Al
O
O
O
O O
Peak at ~ 3600 cm-1 disappears
M = Si+ or Al
N
O
O
+
(b)
O
N
Pyridine
O
O O
Lewis acid site in
AlMCM-41
Si
M
Si
M
O O
Peak at ~ 1455 cm-1 appears
Figure 3.3: Proposed mechanism of interaction between pyridine molecules with (a)
Brönsted and (b) Lewis acid sites in MCM-41 molecular sieves.
The amount of pyridine (Py) adsorbed on the sample in the acidity study of the
samples can be determined by using Equation 3.5 [53, Appendix A].
Adsorbed Py (µmol. g-1) =
B (cm-1) . Sample surface (cm2)
Adsorption Coef. (cm. µmol-1). Weight (g)
(Equation 3.5)
26
27
In the acidity study of this research, the pyridine FTIR spectra for various
samples were recorded using a Perkin Elmer Spectrum One FTIR spectrometer as the
following procedure. About 10 – 15 mg of solid sample was pressed into a selfsupporting wafer (without KBr) of 13 mm diameter and was preactivated under
vacuum (10-6 mbar) at 200 oC for 3 h. The sample was cooled to room temperature
prior to record the background spectrum. The pyridine was then introduced to the
sample for 1 minute. The pyridine was then desorbed at 150 oC, 250 oC and 350 oC.
Finally, the spectrum was then recorded with a 4 cm-1 resolution and 10 scans in the
range of 1650 – 1400 cm-1. A sketch of the pyridine adsorption device is shown in
Figure 3.5.
Pyridine
Mercury
Sample
holder
Infrared
cell
Pump
Figure 3.4: Adsorption and desorption of pyridine apparatus for acidity study.
27
28
3.5.7
Hammett Acidity Analysis
Acid strength of the catalyst can be determined by the Hammett indicator
method. Prior to the analysis, 0.2 g of sample was pretreated by being heated at 473 K
for 2 h in order to remove water, cooled to room temperature and contacted to the
Hammett indicator in dried cyclohexane. The acidic strength was determined by
observing the colour change of the indicator adsorbed on the surface of the sample.
The change of colour of the indicator shows that the acid strength of the sample is
stronger than the indicator used. The acid strength is expressed by the Hammett
acidity function, Ho, corresponding to the pKa of the indicator whereby the formula is
shown in Equation 3.6 [54]. There are many types of organic compounds that used as
Hammett Indicators as shown in Table 3.2.
Ho = pKa + log
[B]
[BH+]
(Equation 3.6)
Table 3.2: The organic compounds used as Hammett Indicators.
Hammett Indicators
3.6
pKa
Chalcone
– 5.60
Anthraquinone
– 8.20
4-Nitrotoluene
–11.35
1-Chloro-4-nitrobenzene
–12.70
2, 4-Dinitrotoluene
–13.75
2,4-dinitrofluorobenzene
–14.52
1,3,5-trinitrobenzene
−16.04
Dibenzoylation of Biphenyl Reaction over Sulphated AlMCM-41
The dibenzoylation reactions of biphenyl were performed at a desired
temperature under batch and dried nitrogen gas flow conditions. For each test, the
mesoporous materials (0.5 g) were activated for 2 h at 200 °C to eliminate water and
28
29
gases adsorbed before transferring the sample to the reaction vessel under N2
atmosphere. Next, a mixture of biphenyl (0.154 g, 1.0 mmol), benzoyl chloride (10
ml, ~85.0 mmol) and hexadecane (25 µL) were added. Hexadecane was used as an
internal standard while yields were based on the biphenyl since benzoyl chloride was
used in excess. Samples were taken out and the samples were centrifuged before
analysis to avoid deposit of solid material on the capillary column. The products
acquired were monitored by GC-MSD (HP-5MS capillary column) and verified by
GC-FID (Equity 1 capillary column).
GC (Thermofinnigan’s Chrom-Card S/W for Trace/FocusTM GC) equipped
with a flame ionization detector (FID) and a non-polar capillary column (Equity 1)
was utilized to verify the products produced. The sample was analyzed by split
method with nitrogen (N2) as the carrier gas. The GC-FID oven and inlet programmes
setup for identifying 4, 4’-DBBP are given as in Table 3.3.
Table 3.3: GC-FID oven-programmed setup for identifying 4, 4’-DBBP.
Parameter
Inlet temperature
Split flow
Right carrier pressure
Initial temperature
Hold time
1st rate
1st final temperature
Hold time
Condition
260 oC
10 ml /min
170 kPa/24.65 psi
40 oC
1.00 min
15.0 oC/min
300 oC
15.00 min
GC-MS (Agilent 6890N-5973 Network Mass Selective Detector) is equipped
with HP-5MS column (30m × 0.251 mm × 0.25 µm), diffusion pump and
turbomolecular pump. Sample was analyzed on splitless method with helium (He) as
the carrier gas. The inlet and oven-programmed setups are presented as in Table 3.4.
29
30
Table 3.4: GC-MSD oven-programmed setup for identifying 4, 4’-DBBP.
Parameter
Inlet temperature
Right carrier pressure
Total flow
Initial temperature
1st rate
1st final temperature
Hold time
3.6.1
Condition
320 oC
170 kPa / 24.65 psi
24 ml / min
60 oC
15.0 oC/min
310 oC
30.0 min
Dibenzoylation of Biphenyl Reaction over Various Types of Catalysts
In order to compare the activity of sulphated AlMCM-41, H-AlMCM-41,
sulphated amorphous silica and concentrated sulphuric acid were used as comparative
catalysts. The dibenzoylation reactions of biphenyl were performed at the same
condition. The 0.5 g of H-AlMCM-41 and sulphated AlMCM-41 were activated at
400 oC and 200 oC for 2 h, respectively before conducting the reaction. For the
catalyst such as sulphuric acid, 30 µL of sulphuric acid 95-97% of were used for
catalytic comparison. Furthermore, sulphated amorphous silica was prepared using
the same method like in Section 3.4 whereby RHA was used as silica source.
3.6.2
Synthesis of 4-PBP as authentic sample
Monosubstituted 4-PBP was prepared by treatment of benzoyl chloride (2.33
ml, 20 mmol) with AlCl3 (4.00 g, 30 mmol) in chloroform at room temperature for 15
min. Biphenyl (3.08 g, 20 mmol) was then added into the mixture. The mixture was
stirred and refluxed for 4 h. The resulting mixture was continuously stirred and then
quenched with water until two separated layers were observed. Next, the organic layer
was separated and rotary evaporated. Ethanol (5 ml) was added and the resulting
mixture was allowed to cool in an ice bath to give a white solid, namely 4-
30
31
phenyl benzophenone (2.32 g) with melting point 99 oC. The infrared and mass
spectra are shown in APPENDIX B and C.
3.6.3
Synthesis of 4-DBBP as authentic sample
4, 4’-DBBP was prepared via homogeneous Friedel-Crafts dibenzoylation
reaction. Benzoyl chloride (2.800 g, 20 mmol), biphenyl (0.308 g, 2 mmol) and a
magnetic bar were put into a two-necked round bottom flask. Benzoyl chloride acted
as the benzoylating agent and solvent. The mixture was cooled with ice and the twonecked round bottom flask was attached to a condenser with the upper part connected
to a supply of nitrogen gas. AlCl3 (3.4788 g, 26 mmol) was then immediately but
gradually added until a dark reddish lump was observed. The residue was stirred
under cool condition for 5 minutes, followed by stirring at 85 oC for 12 h. The lump
was let to cool at room temperature and the lump was transferred little by little into an
ice bath by using a spatula to give a yellowish solid. The solids were filtered and dried
in the oven at 100 oC overnight. The solids were mixed with activated carbon (0.5 g)
in a round bottom flask containing toluene (25 ml), followed by heating at 80 oC for
15 min under stirring. The resulting mixture was immediately filtered and the filtrate
was allowed to cool in an ice bath. A white solid was crystallized, filtered, rinsed
carefully for a few times with acetone. The purification using activated carbon and
recrystallization processes were repeated for two times in order to obtain pure 4, 4’DBBP. Finally, the last traces of acetone was removed by drying in oven at 100 oC
overnight to give white and shiny 4, 4’-DBBP (0.1648 g), m.p. 218 °C. The infrared
and mass spectra are shown in APPENDIX D and E.
3.6.4
Calibration Curve for Authentic Sample
In this research, the calibration linear curves of biphenyl, 4-PBP and 4, 4’-
DBBP standards with variety of concentrations were plotted. The graphs were plotted
with area ratio (area of peak of reactant or product / area of peak of hexadecane)
31
32
which is obtained by using GC as Y-axis while concentration as X-axis. By applying
the authentic sample calibration curves, the amount of biphenyl consumed and the
production of 4-PBP and 4, 4’-DBBP in every reactions were able to be quantified.
Figure 3.5, 3.6 and 3.7 show the quantitative calibration plots of biphenyl, 4-PBP and
4, 4’-DBBP authentic samples analyzed by GC, respectively.
3.5
3.0
Area Ratio
2.5
y = 3.1338x
2.0
2
R = 0.9837
1.5
1.0
0.5
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Biphenyl / mmol
Figure 3.5: Quantitative calibration plot of biphenyl.
4.5
4.0
Area Ratio
3.5
3.0
2.5
2.0
y = 3.1596x
2
R = 0.987
1.5
1.0
0.5
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
4-PBP / mmol
0.8
0.9
1.0
1.1
Figure 3.6: Quantitative calibration plot of 4-PBP.
32
33
0.7
0.6
Area Ratio
0.5
y = 3.1207x
0.4
2
R = 0.9953
0.3
0.2
0.1
0.0
0.00
0.05
0.10
0.15
0.20
4, 4'-DBBP / mmol
Figure 3.7: Quantitative calibration plot of 4, 4’-DBBP.
33
34
CHAPTER 4
RESULTS AND DISCUSSION
4.1
X-Ray Diffraction Analysis
The XRD patterns for uncalcined AlMCM-41 and calcined AlMCM-41 are
shown in Figures 4.1 and 4.2, respectively. As displayed in the figures, the samples
exhibit an intense signal at about 2θ = 2.2 o due to (100) plane and weak signals between
3.5–6.0o due to (110), (200) and (210) planes. These peaks are typical of MCM-41
materials which confirm the hexagonal mesophase of the materials [26]. The
diffractogram shown in Figure 4.2 shows that the catalyst with low aluminium content
shows more than three resolved diffraction peaks, indicating highly ordered structures.
On the other hand, the XRD patterns for the catalysts with higher alumina content of
MCM-41 give weakly resolved peaks, suggesting loss of structural order of the materials.
Hence, it can be concluded that Al content in mesoporous MCM-41 influences the long
range of order.
It can also be observed that the peak intensity of the XRD pattern of MCM-41
material increases after calcination implying more ordered framework structure as a
consequence of template removal [53]. In addition, the XRD peaks shift to higher dvalues as aluminium content increases, indicating an increase in the unit cell parameters.
The increase in unit cell parameter is expected as the aluminium content increased due to
the larger ionic size of trivalent aluminium (0.48 Å) than tetravalent silicon (0.41 Å)
incorporates into the MCM-41 structure [55]. Table 4.1 summarizes the average unit cell
parameters (ao) for various samples calculated by using the higher order reflexes as well
as the dominant low angle (100) peak.
After ion exchange with NH4NO3, a decrease of the corresponding peaks in the
XRD patterns of H-AlMCM-41 occurred, indicating a deterioration of the mesoporous
34
35
structure. It is described as in Figure 4.3. In addition, an impregnation of H-AlMCM-41
with sulphuric acid results in the decrease of peak intensity indicating damage of
mesoporous structure as shown in Figure 4.4. Besides that, a decrease of the value of dspacing and unit cell parameter was observed, showing a decrease in pore diameter. It can
be proven with the decreasing of pore volume of the sulphated sample shown in Table
4.2. In addition, the results obtained by using Sherrer Equation shows that the crystallite
size of sulphated MCM-41 samples decrease after ion exchange modification. From the
data obtained, it can be said that a decrease in pore diameter and surface area may be due
to the transition part of the crystalline phase of sulphated MCM-41 materials to
amorphous phase.
Table 4.1: XRD data of various MCM-41 samples.
Sample
SiO2/Al2O3
d-spacing (Å)
ao
t (Å)†
Ratio
(100)
(110)
(200)
(210)
(Å)*
UNCAL-1
∞
40.05
23.59
20.44
15.42
46.24
24.36
UNCAL-2
60
40.60
23.66
20.45
15.44
46.88
20.01
UNCAL-3
30
41.06
23.82
20.61
–
47.41
15.18
UNCAL-4
15
44.07
24.35
21.31
–
50.88
14.29
CAL-1
∞
36.89
21.15
19.82
15.46
42.60
29.39
CAL-2
60
37.83
21.88
19.09
15.47
43.68
21.90
CAL-3
30
38.94
22.50
19.65
–
44.96
16.87
CAL-4
15
39.81
22.93
19.67
–
45.97
16.20
HCAL-1
∞
37.68
21.80
18.21
–
43.51
26.61
HCAL-2
60
37.98
21.90
18.98
–
43.86
20.40
HCAL-3
30
37.84
21.94
18.98
–
43.69
16.39
HCAL-4
15
38.16
21.92
19.14
–
44.06
15.18
SCAL-1
∞
37.18
21.50
18.52
–
42.93
23.31
SCAL-2
60
37.15
21.72
18.78
–
42.90
19.04
SCAL-3
30
37.54
21.69
18.91
–
43.35
15.60
SCAL-4
15
37.89
21.82
18.85
–
43.75
15.57
* a o = 2 d 100 / 3
†
t = 0.9 λ / (B cos θ)
35
36
2700
(100)
2600
2500
2400
2300
2200
2100
2000
1900
Intensit
Intensi
Int
ensity (Cps)
1800
1700
1600
1500
1400
1300
1200
(d)
1100
1000
(c)
900
800
700
(b)
600
500
(110) (200)
400
300
(210)
(a)
200
100
0
1.5
2
3
4
5
6
7
8
9
10
2θ
Figure 4.1: X-ray diffractogram patterns of uncalcined mesoporous MCM-41
molecular sieves. (a) UNCAL-1, (b) UNCAL-2, (c) UNCAL-3 and (d)
UNCAL-4.
(100)
7000
6000
Inte
Intensit
nsity (Cps)
Intensity
(Cps)
5000
4000
(d)
3000
(c)
2000
(b)
(110) (200)
1000
(a)
(210)
0
1.5
2
3
4
5
6
7
8
9
10
2θ
Figure 4.2: X-ray diffractogram patterns of mesoporous MCM-41 materials after
calcinations at 550 oC for 10 h. (a) CAL-1, (b) CAL-2, (c) CAL-3 and
(d) CAL-4.
36
37
Intensity (Cps)
Intensity
(100)
(d)
(c)
(b)
(110) (200)
(a)
0
1.5
2
3
4
5
6
7
8
9
10
2θ
Figure 4.3: X-ray diffractogram patterns of protonated MCM-41 materials (a) HCAL1, (b) HCAL-2, (c) HCAL-3 and (d) HCAL-4.
Intensity (Cps)
(100)
(d)
(c)
(b)
(110) (200)
1.5
2
3
4
(a)
5
6
7
8
9
10
2θ
Figure 4.4: X-ray diffractogram patterns of sulphated MCM-41 materials (a) SCAL1, (b) SCAL-2, (c) SCAL-3 and (d) SCAL-4.
37
38
4.2
Infrared Spectroscopy of AlMCM-41 Molecular Sieves
Infrared spectroscopy has been used extensively for the characterization of
porous materials. The infrared spectra of the uncalcined and calcined MCM-41
molecular sieves are presented in Figure 4.5. The broad peak around 3420 cm-1 is due
to O-H stretching of water. On the other hand, the bands at around 2924 and 2854
cm-1 are assigned to symmetric and asymmetric stretching modes of the C-H sp3
groups of the template. Their corresponding bending mode of C-H is observed at
~1480 cm-1. The peak at around ~1640 cm-1 corresponds to bending mode of O-H of
water. Besides, the peaks around 1229 and 1084 cm-1 are attributed to the asymmetric
stretching of Si-O-Si groups. The symmetric stretching modes of Si-O-Si groups are
observed at around 799 and 578 cm-1. The peak at 965 cm-1 is assigned to the presence
of defective Si-OH groups while the adsorption band at ~455 cm-1 corresponds to
bending vibration of Si-O-Si or Al-O-Si groups. Figure 4.6 shows the FTIR spectra of
calcined mesoporous MCM-41 molecular sieves. It can be inferred that the symmetric
and asymmetric modes of the C-H sp3 group of the template are absent in the range of
2900 and 1480 cm-1, indicating that the template has been successfully removed [5].
Figure 4.7 shows FTIR spectrum of sulphated AlMCM-41 samples. It can be
observed that there are a few additional peaks in FTIR spectrum of sulphated
AlMCM-41. The additional band at 1071 cm-1 corresponds to the stretching vibration
of the S=O bond is clearly visible for the sulphated AlMCM-41. The absorption band
at 1180 cm-1 is due to symmetric vibrations of Si–O–S bridges. Apart from that, the
band observed at 888 cm-1 is due to symmetric S–O stretching vibrations whereas the
SO2 deformation has been assigned in the region 580 cm-1 [43, 44].
38
39
UM-1
578
795
3404
2854
2924
1652 1486
454
1233
UM-2
1065
588
3405
2854
2924
%Transmittance
%T
1640 1480
800
457
1230
UM-3
1070
%T
1644
795
581
1482
3422
2854
2923
453
1223
1062
UM-4
793
1645
3423
588
1481
2855
2924
451
1222
1064
4000.0
3000
2000
1500
1000
400.0
cm-1/ cm-1
Wavelength
Figure 4.5: FTIR spectra of uncalcined mesoporous MCM-41 molecular
M-1
1638
963 802
3456
1236
463
1084
M-2
1638
%T
960 803
%Transmittanc
e
ittance
3445
1239
463
M-3
%T
1080
1636
801
960
461
3451
1233
M-4
1636
1080
799
3451
466
1234
4000.0
3000
2000
1500
1083
1000
400.0
cm-1
Wavelength
/ cm-1
Figure 4.6: FTIR spectra of calcined mesoporous MCM-41 molecular sieves.
39
40
SM-1
1638
1285
SM-2
964
% Transm itta nce
809
883
S-O
580 460
Si-O-S
S=O
SO2
1178 1078
deformation
3408
%T
960
SM-3
1637
809
884
1285
581 458
3406
1180 1079
806
963 885
1639
580
3417
1288
SM-4
457
1175 1084
806
1639
964 884
1288
3419
4000
580 458
1179 1077
3000
2000
1500
-1
Wavelength
cm-1 / cm
1000
400
Figure 4.7: Infrared spectra of sulfated AlMCM-41 molecular sieves.
4.3
Nitrogen Adsorption Measurement
Table 4.2 shows the textural properties for the protonated and sulphated
MCM-41 mesoporous materials. The results infer that modification of the samples
through sulphation leads to a decrease in both surface area as well as pore volume.
The changes in pore volume are due to the transition of crystalline phase to
amorphous phase. This finding is in line with the XRD data where the crystallite size
and degree of crystallinity decrease after sulphation. Apart from that, further
investigation also reveals that the pore diameter decrease steadily for the sulphated
samples with increment in aluminium content. The shrinkage of pore diameter
happens due to dealumination of aluminium and is being migrated to the surface of
MCM-41 followed by sulphation towards the aluminium. These sulphated aluminium
species will cover the surface of the pore, leading to reduction of pore diameter and
pore volume as illustrated in Figure 4.8. Hence, the pore diameter will become
smaller as more sulphated aluminium species is in the sample. Meanwhile, the pore
40
41
wall thickness for all protonated samples remains fairly constant. However, its
thickness increases after sulphation. It may due to deposition of sulphated aluminium
species on the pore walls, leading to increment in pore wall thickness.
Table 4.2: The textural properties of various protonated and sulphated MCM-41
samples obtained from calculation and surface analyzer.
Sample
BET surface
Pore volume,
Pore wall thickness,
Pore diameter,
area (m2/g)
Vp (cm3/g)
bd ** (Å)
Wd * (Å)
HCAL-1
1194
0.73
19.12
35.88
HCAL-2
1131
0.74
19.18
36.26
HCAL-3
1072
0.77
18.85
36.40
HCAL-4
1059
0.79
18.84
36.88
SCAL-1
527
0.59
20.30
33.89
SCAL-2
635
0.50
21.48
32.61
SCAL-3
482
0.29
26.02
28.42
SCAL-4
549
0.28
26.56
28.38
* Wd = C d100
⎛ ρV p
⎜
⎜ 1 + ρV
p
⎝
1
⎞2
⎟
⎟
⎠
** bd = 2(3-1/2)d100 – Wd/1.050
bd
bd
Wd
Sulphation
Wd
= Sulphated Al species
Figure 4.8: Modification of surface of MCM-41 through sulphation leads to
shrinkage of pore diameter.
41
42
4.4
Thermal Analysis
The TG profile of the uncalcined sample (UNCAL-2) is depicted in Figure
4.9. Basically, the TG of uncalcined sample follows a three-stage weight loss. The
first stage loss (around 5 %) was due to desorption of water and adsorbed gas
molecules (<200 oC). In the second stage, a high-temperature weight loss peak
(around 33%) around from 200 to 450 oC was also observed, which might correspond
to the decomposition of template in the samples via Hofmann elimination [56]. The
third stage weight loss (around 3%) was due to water produced by thermal
condensation of silanol groups to siloxane groups (450-550 oC). The data obtained for
the as-synthesized materials are in good agreement with those reported by Busio et al.
[57].
Graph 1:Weight Loss (%) vs. Temperature (oC)
Graph 2: Heat Flow Exo Up (mW) vs temperature (oC)
100
Weight (wt. %)
95
30
90
25
85
20
80
75
15
Graph 2
70
10
65
Graph 1
60
5
Heat Flow Exo Up (mW)
35
0
55
0
100
200
300
400
o
500
600
700
800
Temperature ( C)
Figure 4.9: Thermogravimetric analysis of uncalcined MCM-41 sample (UNCAL-2)
in nitrogen gas with 20 oC/min heating rate.
42
43
Figure 4.10 demonstrates the percentage of weight versus the temperature plot
of a series of uncalcined MCM-41 materials. It can be observed that the high amount
of template removed occurs at higher temperature when the aluminium content
increases. It is due to the additional electrostatic forces exist between template cations
and aluminium sites. The more aluminium sites in the sample, the stronger attraction
of it towards the template cations. Therefore, more energy is needed in order to
overcome the forces prior to removing the template from the sample. The template
cations bonded to siloxy groups decompose at low temperature and those associated
with aluminium sites at high temperature [57].
Figure 4.10: Thermogravimetric analysis of uncalcined MCM-41 samples with
various ratio of SiO2/Al2O3.
Figure 4.11 shows the thermograms of a series of protonated MCM-41
materials. From the thermogravimetry measurement, it is not able to show a
significant change as SiO2/Al2O3 decreases. However, all the samples show a
remarkable weight loss below 100 oC due to desorption of water and adsorbed gas
molecules, and a slight weight loss after 100 oC owing to water produced by thermal
condensation of silanol groups.
43
44
Figure 4.11: Thermograms of a series of protonated MCM-41 molecular sieves.
Figure 4.12 demonstrates the TG-DTAprofiles taken in air of H2SO4
impregnated on MCM-41 materials with various SiO2/Al2O3 ratios. It can be observed
that the SCAL-2, SCAL-3 and SCAL-4 follow almost the same trend except for
purely siliceous SCAL-1. All the samples exhibit four stages of weight loss, from 150
o
C – 300 oC and 300 oC – 600 oC owing to decomposition of sulphate groups attached
on MCM-41 molecular sieves. Besides, thermal condensation of silanol groups to
siloxane groups also occurs at the range of 450 oC – 550 oC. From the data obtained,
protonated MCM-41 followed two steps of weight loss whereas the sulphated MCM41 involved four steps of weight loss, verifying that the sulphate groups were
successfully interacted with the surface of MCM-41. It is demonstrated in Figure 4.18
that the intensity of peak assigned to silanol group deceases after modification of
sulphuric acid.
44
45
Figure 4.12: Thermogravimetric curves of sulphated AlMCM-41 materials.
4.5
Solid State Nuclear Magnetic Resonance Spectroscopy
4.5.1
27
Al MAS NMR
Figure 4.13 and 4.14 show the
27
Al MAS NMR spectra of protonated and
sulphated MCM-41 samples, respectively. The spectra of the former show two intense
signals at ~ 54 ppm and 0 ppm corresponding to the tetrahedral aluminium in the
framework structure and octahedrally coordinated extra-framework aluminiums
(EFAL), respectively [5]. Meanwhile, the increment in intensity of both peaks
increaseas can be shown in Table 4.3 where the peak area calculated from mass
analysis increases as the aluminium content increases.
45
46
Figure 4.13:
27
Al NMR spectra of protonated MCM-41 molecular sieves (a) HCAL-
1, (b) HCAL-2, (c) HCAL-3 and (d) HCAL-4.
Figure 4.14:
27
Al NMR spectra of sulphated MCM-41 molecular sieves (a) SCAL-1,
(b) SCAL-2, (c) SCAL-3 and (d) SCAL-4.
46
47
Table 4.3: Peak areas of octahedral aluminium (Aloct) and tetrahedral aluminium (Altet)
from 27Al MAS NMR spectra.
Samples
Altet (%)
Aloct (%)
Aloct/Altet ratio
HCAL-1
–
–
–
HCAL-2
65.05
34.95
0.54
HCAL-3
66.44
33.56
0.51
HCAL-4
77.87
22.13
0.37
There is no signal observed in the SCAL-1 due to absence of aluminium in the
framework. From the spectra of SCAL-2, SCAL-3 and SCAL-4 in Figure 4.14, it can
be observed that the peak at ~ 54 ppm which is attributed to tetrahedrally coordinated
aluminium is not observed for all of the sulphated samples. However, two sharp peaks
are detected at ~ 0 ppm and ~ –5 ppm with an increase of peak intensity as the
aluminium content increase. Table 4.4 shows the data of peak areas of octahedral
aluminium species in aluminium sulphate and sulphated aluminium from
27
Al MAS
NMR spectra as calculated from cut and weight method.
Table 4.4: Peak areas of octahedral aluminium species in aluminium sulphate
(AlAl2(SO4)3) and sulphated AlMCM-41 (AlSulphated
AlMCM-41)
from
27
Al
MAS NMR spectra.
Samples
AlAl2(SO4)3
(%)
AlSulphated
AlMCM-41
(%)
AlSulphated AlMCM-41 /
AlAl2(SO4)3 ratio
SCAL-1
–
–
–
SCAL-2
81.63
18.37
0.22
SCAL-3
82.66
17.34
0.21
SCAL-4
84.24
15.76
0.18
47
48
The signal ~ 0 ppm is assigned to octahedrally coordinated extra-framework
aluminium (EFAL). These peaks perhaps originate from EFAL present in the form of
Al3+, AlO+ or Alx(OH)yn+. The other signal at ~ –5 ppm is an unknown signal which
have to be investigated further. However, we predict that this is the peak due to EFAL
with different chemical environment. In order to prove this, the sulphated AlMCM-41
was treated with 1.0 M methanolic HCl solution. The results show that the 27Al MAS
NMR spectrum did not exhibit any peak at the range of 0 ppm due to removal of
EFAL by treatment with methanolic HCl solution. Therefore, it confirms that the
signal at ~ –5 ppm is contributed to another type of EFAL and impregnation of
sulphuric acid can lead to framework dealumination.
Conventionally, Lewis acidity is attributed to octahedrally coordinated
aluminium. Since the peak for tetrahedral aluminium was not observed by 27Al MAS
NMR, therefore Brönsted acidity was not expected to exist in sulphated AlMCM-41.
However, this implication contradicts that made by the pyridine-FTIR spectroscopy
whereby sulphated MCM-41 samples show no Lewis acid sites but possesses high
amount of Brönsted acid sites instead. Therefore the existence of Brönsted acid sites
in these samples, which has never been observed in similar system before, must be
due to the introduction of sulphate group (HOSO3–) into the sample that may have
formed bond with the octahedral aluminium.
In order to assign the two peaks observed in the sulphated AlMCM-41,
quantitative
27
Al MAS NMR whereby a sample containing a mixture of both
sulphated AlMCM-41 and aluminium sulphate (50:50) was used. Knowing that
aluminium in aluminium sulphate is octahedral [58], therefore one of the peaks was
matched to octahedral aluminium found in aluminium sulphate. The result shows that
there are two types of Al in the sample. The intensity of the peak at ~ 0 ppm
increases, indicating that the peak is due to aluminium sulphate while the peak at ~ –5
ppm is due to Si–O–Al(OSO3H)53-. The chemical shift of the Al in Si–O–
Al(OSO3H)53- can be predicted. SiO- attached to Al is less electronegative than HSO4and will shield Al more in SiO–Al (OSO3H)53-, resulting in an upfield shift. As a
result, the shift of the signal to the right on the spectrum is observed.
48
49
From observation by us and other researchers, it is found that the types of acid
sites are changed when a different solvent is used in sulphation of AlMCM-41 [33-35,
44, 59]. This phenomenon is believed to be due to the hydrophobic properties of the
solvent. Water which is a hydrophilic solvent would hydrolyze the sulphate groups
attached to the AlMCM-41, producing Lewis acid sites. However, hydrophobic
organic solvent such as hydrated toluene could protect sulphate groups from being
hydrolyzed and hence produce Brönsted acid sites.
4.5.2
29
Si MAS NMR
Figure 4.15 presents the
29
Si MAS NMR spectrum of sulphated MCM-41
sample (SM-4). The spectrum exhibits very broad peak which resemble that of
amorphous silica. Apart from that, the spectrum also reveals the presence of five
species of silicon. The signal at -59 ppm corresponds to the Si(OAl)4 or Q0 species
while the shoulder at -81 ppm might due to Si(OSi)(OAl)3 or Q1 and Si(OSi)2(OAl)2
or Q2 species. Meanwhile, a peak at -96 ppm which might assign to Si(OSi)3(OAl) or
Q3 species. Moreover, a weak shoulder at -108 ppm is detected which is responding to
Si(OSi)4 or Q4 species.
Table 4.5 shows the peak areas of silicon species in SM-4. The table
demonstrates that about 60.7% of silicon in SCAL-4 exists as Q3 species while only
2.9% of silicon exists as Q0 species. Form the data, it can be observed that the
existence of Q3 species is more preferable. The big molecules of sulphated aluminium
would contribute to steric hindrance and form unstable alumino-silicon species. In
contrast, SiO- molecule is more favourable in binding with silicon atom because of its
smaller molecular size. Figure 4.16 shows the possible silicon species and Brönsted
acid sites in sulphated AlMCM-41. The scheme considers that the material surface is
totally dehydrated, which is obtained after activation at 200 oC, with the sulphate
covalently bonded to the aluminium and silicon via oxygen atoms. The negative
charge of the complex is neutralized and balanced by H+ cation.
49
50
Q3
Q1 and Q2
Q4
Q0
Figure 4.15:
29
Si NMR spectrum of sulphated MCM-41 molecular sieves (SCAL-4).
Table 4.5: Peak areas of silicon species in SCAL-4.
Silicon species
Qn
Peak areas (%)
Si(OAl)4
0
2.93
Si(OSi)(OAl)3
1
Si(OSi)2(OAl)2
2
Si(OSi)(OAl)3
3
60.70
Si(OSi)4
4
7.92
28.45
50
51
3H+
OAl(OSO3H)53-
Q0
3H+
Si
3-
(HO3SO)5AlO
3H+
OAl(OSO3H)5
Q2
3H+
3-(HO SO) AlO
3
5
3H+
3-(HO SO) AlO
3
5
OAl(OSO3H)5
O
Si
Al2(SO4)3
OAl(OSO3H)533H+
Q1
3H+
3-
3-
Si
OAl(OSO3H)533H+
Q3
3H+
OAl(OSO3H)53-
Si
3H+
OAl(OSO3H)53-
OSO3H
Si
Si
O
O
O
Si
Si
Si Si
O
O
O
Si
Si Si
O
O
Si
MCM-41 surface
Figure 4.16: The possible silicon species and Brönsted acid sites in sulphated
AlMCM-41.
4.7
Acidity Measurements
4.7.1
Pyridine-FTIR Spectroscopy
Figure 4.17, 4.18 4.19 and 4.20 show the pyridine-FTIR spectra of sulphated
AlMCM-41 with various SiO2/Al2O3 ratios. The band at 1446 cm-1 is attributed to
physisorbed pyridine and this band decreases sharply at 150 oC. Besides, it can be
observed that all the samples exhibit bands at 1546 and 1496 cm-1. The existence of a
band at 1496 cm-1 assigned to pyridine associated with both Brönsted (B) and Lewis
(L) acid sites and a band at 1540-1550 cm-1 attributed to pyridine bound to Brönsted
acid sites [5]. It can also be seen that increment in aluminium content leads to
increment of the amount of Brönsted acid sites as given in Table 4.6. Sulphated
MCM-41 materials with SiO2/Al2O3 = 15 (SCAL-4) shows the highest amount of
Brönsted acid sites whereas siliceous SCAL-1 shows the lowest amount of Brönsted
acid sites. This phenomenon happens because the more aluminium atoms existed in a
sample, more sulphate group (HOSO3–) may form bonding with the atom to form
octahedrally extra-framework aluminium. Moreover, no Lewis acid site was observed
51
52
for all the samples since there is no peak at ~1455 cm-1. This result combined with the
27
Al MAS NMR data show that Brönsted acidity in sulphated MCM-41 is attributed
to octahedrally coordinated aluminium since the peak for tetrahedral aluminium was
not observed by 27Al MAS NMR
The figures also depict pyridine-FTIR spectra of sulphated AlMCM-41 at
different temperatures. It is clear from the figures that as the desorption temperature is
increased, the Brönsted acidic sites bound pyridine band intensity decreases gradually.
Figure 4.21 shows the FTIR spectra of protonated (HCAL-1) and sulphated (SCAL-1)
siliceous MCM-41 at the range of 3200 – 3900 cm-1. It demonstrates that the intensity
of the signal at ~ 3740 cm-1, attributed to silanol group decreases significantly after
treatment with sulphuric acid. It indicates that the sulphate groups not only reacted
with Al–OH but also with Si–OH groups, which lead to enhancement of Brönsted
acidity sites.
B
B+L
L
(d)
Absorbance / A
(c)
(b)
(a)
1650 1620 1600 1580 1560 1540 1-1 520 1500 1480 1460 1440 1420 1400
Wavelength / cm-1
Figure 4.17: The pyridine-FTIR spectra of Purely siliceous MCM-41 (SCAL-1) at
(a) room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC.
52
53
(d)
B
B+L
L
Absorbance / A
(c)
(b)
(a)
1650 1620 1600 1580 1560 1540 1520
1500 1480 1460 1440 1420 1400
1
-1
Wavelength / cm
Figure 4.18: The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-2) at (a)
room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC .
(a)
B
B+L
L
Absorbance / A
(b)
(c)
(d)
1650 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400
Wavelength / cm-1
Figure 4.19: The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-3) at (a)
room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC .
53
54
(d)
B+L
(c)
L
Absorbance / A
B
(b)
(a)
1650 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400
Wavelength / cm-1
Figure 4.20: The pyridine-FTIR spectra of sulphated AlMCM-41 (SCAL-4) at (a)
room temperature, (b) 150 oC, (c) 250 oC and (d) 350 oC.
Table 4.6: Pyridine FTIR data of protonated and sulphated MCM-41 materials.
µmol Pyridine g-1
Catalyst
Brönsted
Lewis
25 oC
150 oC
250 oC
350 oC
25 oC
150 oC
250 oC
350 oC
HCAL-1
–
–
–
–
–
–
–
–
HCAL-2
15.5
15.3
15.3
9.3
406.6
21.3
39.9
38.2
HCAL-3
16.3
16.1
15.0
10.7
472.3
49.4
35.6
35.4
HCAL-4
25.1
24.6
19.8
12.5
434.1
52.8
43.5
42.7
SCAL-1
125.7
112.6
32.8
5.2
–
–
–
–
SCAL-2
188.9
180.4
89.0
27.1
–
–
–
–
SCAL-3
199.5
192.0
112.3
38.6
–
–
–
–
–
–
SCAL-4
226.5
215.4
112.9
39.2
–
–
* Si/Al ratio calculated from compositions of starting gel mixtures.
54
Absorbance / A
55
Wavelength / cm-1
Figure 4.21: FTIR spectra of silanol groups of MCM-41 materials at 250 oC (a)
before treatment (HCAL-1) and (b) after treatment (SCAL-1) of
sulphuric acid.
4.7.2
Hammett indication Analysis
Table 4.7 shows the results of acidity test by using Hammett indicators. From
the table, it can be observed that H-AlMCM-41 and concentrated sulphuric acid were
only able to change the basic forms (colourless) of chalcone (pKa = –5.6),
Anthraquinone (pKa = –8.2) and 4-nitrotoluene (pKa = –11.35) to yellow colour,
indicating that its acidity is in the range of –11.35 < Ho < –12.70. However, sulphated
AlMCM-41 gives an outstanding result where this solid catalyst turned the basic
forms (colourless) of 2, 4-dinitrotoluene (pKa = –13.75) and its acid strength is
estimated to be −13.75 < Ho < −14.52. This indicates that sulphated AlMCM-41 is a
stronger acid than sulphuric acid.
55
56
Table 4.7: The results of acid strength of catalysts using Hammett indicators.
Hammett
Indicators
Chalcone
Anthraquinone
4-Nitrotoluene
1-Chloro4-nitrobenzene
2, 4-Dinitrotoluene
2,4-dinitrofluorobenzene
Results
pKa
H2SO4
ZSM 5*
HCAL
-1
HCAL
-2
HCAL
-3
HCAL
-4
SCAL1
SCAL2
SCAL3
SCAL4
–5.60
√
√
×
√
√
√
√
√
√
√
–8.20
√
√
×
√
√
√
√
√
√
√
–11.35
√
√
×
√
√
√
√
√
√
√
–12.70
√
√
×
×
×
×
√
√
√
√
–13.75
×
√
×
×
×
×
×
√
√
√
–14.52
×
×
×
×
×
×
×
×
×
×
* ZSM-5 with Si/Al=25
56
57
4.8
Catalytic testing: Dibenzoylation of Biphenyl
Dibenzoylation of biphenyl with benzoyl chloride was chosen as the model
reaction to study the activity of sulphated AlMCM-41 as catalyst. The reaction is
expected to give 4, 4’-DBBP. In order to verified the products acquired, GC-MSD and
GC-FID were applied. GC-FID was chosen as the method for qualitative and
quantitative idenficattion in which the comparison was based on similar retention time
between resulting compound and 4, 4’-DBBP standard while GC-MSD was used to
verified the molecular weight characteristic of the compound. The investigation
subsequently was carried out to study the effect of type of catalyst activity where HAlMCM-41, concentrated sulphuric acid and sulphated amorphous silica were used as
comparative catalysts. The effect of SiO2/Al2O3 ratio, reaction temperature, catalyst
loading and reactants mole ratio was also studied in this study. Finally, the
mechanism of reaction would be proposed.
4.8.1
Effect of Catalyst
In order to study the activity of types of catalyst, protonated HCAL-4,
sulphated amorphous silica, sulphuric acid and sulphated SCAL-4 are tested in the
Friedel-Crafts dibenzoylation reaction. In the absence of catalyst, the yield of 4-PBP
was only 10.8% whereas the dibenzoylation reaction totally did not occur when the
reaction was conducted at 180 oC for 24 h.
In contrast, in the presence of HCAL-4 catalyst, the biphenyl conversion was
increased up to 83.7%. It is shown in Figure 4.22. Unfortunately, this type of catalyst
was inactive towards dibenzoylation of biphenyl reactions. The catalyst was unable to
produce disubstituted product within 24 h, indicating the catalyst shows low activity
towards dibenzoylation reaction. The results indicate that the catalyst is not strong
enough in acidity or amount of acid sites to convert biphenyl into 4, 4’-DBBP due to
dealumination when calcination. Sulphated AlMCM-41 interestingly, exhibited
remarkably high activity and selectivity. This type of catalyst is able to convert 83.2%
57
58
of biphenyl into monosubstituted product within 24 h, proving high performance
towards benzoylation reaction. The sulphated AlMCM-41 prepared by secondary
impregnation method gave the highest activity, whereas the H-AlMCM-41 prepared
by ion-exchange method gave a lower activity towards benzoylation of biphenyl
reaction. It is because of the higher amount of Brönsted acid sites in sulphated
AlMCM-41 (SCAL-4) compared to H-AlMCM-41 (HCAL-4) which provide more
active sites for the reaction.
In comparison, concentrated sulphuric acid shows 75.0% conversion of
biphenyl but poorer selectivity (35.3%) compared with sulphated AlMCM-41 towards
benzoylation reaction. Besides, benzoylation of biphenyl using two catalysts
simultaneously, viz. H-AlMCM-41 and concentrated sulphuric acid gave 90.6%
conversion of biphenyl but poor selectivity (13.0%) towards benzoylation reaction.
Sulphated AlMCM-41 shows higher selectivity because MCM-41 molecular sieves
which have uniform pores could reduce the amount of ortho and meta substituted
product. Such phenomenon is called “shape-selective effect”. Therefore, it is evident
that sulphated AlMCM-41 demonstrated an enhanced activity.
Meanwhile, sulphated amorphous silica was only able to give 22.3%
conversion of biphenyl and it is not active in both benzoylation and dibenzoylation
reactions. Meanwhile, sulphated amorphous silica only able to give 22.3% conversion
of biphenyl and it is not active in both benzoylation and dibenzoylation reactions.
Based on the selectivity of 4, 4’-DBBP after 24 h of reaction time, the trend in
activities for the catalysts studied is as follows: SCAL-4 > Sulphuric acid & HCAL-4
> HCAL-4 ≈ Sulphuric acid > sulphated amorphous silica. Table 4.8 summarizes the
results obtained in terms of conversion of biphenyl, selectivity towards 4-PBP and
activity towards 4, 4’-DBBP by using various form of catalysts.
58
59
90
88.7
83.7
BP
83.2
80
77.7
75.5
4-PBP
4, 4'-DBBP
Concentration (%)
70
Others
60
55.7
50
40
30
25
19.3
16.3
20
9.411.1
4.1
10.8
10
0 0.5
22.1
0 0
11
5.8
0
0
0 0.2
0
Without
1
catalyst
HCAL-4
2
HCAL-4
3 & Sulphuric
4 acid
Sulphuric acid
SCAL-4
5
Sulphated
6
amorphous silica
Figure 4.22: Dibenzoylation of biphenyl catalyzed by various types of catalysts.
Table 4.8: Benzoylation and dibenzoylation of biphenyl with benzoyl chloride over
various types of catalysts at 180 oC for 24 h.
Catalyst(s)
Conversion of Selectivity towards Selectivity towards
BP
4-PBP
4,4’-DBBP
Without catalyst
11.3%
95.6%
0.0%
H2SO4
75.0%
35.3%
0.0%
HCAL-4
73.7%
83.7%
0.0%
H2SO4 & HCAL-4
90.6%
13.0%
1.7%
SCAL-4
94.2%
83.2%
6.4%
Sulphated silica
22.3%
22.1%
0.0%
59
60
4.8.2
Effect of SiO2/Al2O3 ratio
The results obtained for the dibenzoylation of biphenyl over different
SiO2/Al2O3 ratios of sulphated AlMCM-41 are discussed in this section. Figure 4.23
shows the conversion of biphenyl over various ratios of SiO2/Al2O3. It is noticed that
the conversion of biphenyl in the dibenzoylation reaction is markedly affected by the
SiO2/Al2O3 molar ratio of the catalyst where higher the SiO2/Al2O3 ratio of the
materials produce lower conversion of biphenyl. The SCAL-4 seemed to be the
optimum one for showing its highest catalytic activity in the dibenzoylation reaction
of biphenyl whereas the purely siliceous SCAL-1 showed the lowest activity among
the other catalysts. The conversion of biphenyl over SCAL-1, SCAL-2, SCAL-3 and
SCAL-4 within 24 h is found to be 76.9, 90.8, 93.6 and 94.2% respectively while the
yield of 4, 4’-DBBP of the catalysts shown in Figure 4.24 are 4.0, 8.8, 9.3 and 11.0%,
respectively.
100
ConcentrationofofBiphenyl
biphenyl (%)
Conversion
(%)
90
80
70
60
50
SCAL-4
40
SCAL-3
SCAL-2
SCAL-1
30
20
10
0
0
4
8
12
16
20
Time (h)
24
28
32
Figure 4.23: Conversion of biphenyl over various ratio of SiO2/Al2O3 within 24 h.
60
61
12
SCAL-4
SCAL-3
SCAl-2
SCAL-1
10
Yield (%)
8
6
4
2
0
0
4
8
12
16
20
24
28
32
Time (h)
Figure 4.24: Yield of 4, 4’-DBBP over various ratio of SiO2/Al2O3 within 24 h.
4.8.3 Reaction Temperature
In order to study the effect of temperature of the reaction, the SCAL-4 was
chosen as catalyst. The results of this study are shown in Figure 4.25. The
benzoylation and dibenzoylation products increase steadily as the temperature are
raised from 160 oC to 200 oC. It is because an increase of temperature increases the
reaction rate. In principal, a chemical reaction occurs only when the reactant
molecules acquire enough kinetic energy, which needs to overcome the activated
energy, as well as proper orientation of collision. From the kinetic theory, the more
energy provides to the reactant molecules, the faster the molecules move and the more
frequent they collide. As a result, the reaction rate will increase simultaneously. From
this study, SCAL-4 did not give 4, 4’-DBBP after 24 h operation at 160 oC, showing
that the dibenzoylation of biphenyl over sulphated MCM-41 materials only active at
180 oC above. Apart from that, SCAL-4 showed 100% conversion and high yield of 4,
4’-DBBP, i.e. 18.4% at 200 oC. However, the selectivity was poorer due to additional
byproducts in this condition. Nevertheless, dibenzoylation reaction conducted at 180
61
62
o
C, indicated that the selectivity for 4, 4’-DBBP remained nearly constant although
the conversion is only 94.7%.
83.20
BP
4-PBP
4, 4'-DBBP
80.36
90
80
Concentration (%)
60.34
Others
70
60
50
40.19
40
18.42
30
10.42
20
5.80
0.00 0.00
10
1.52
0.00 0.00
0
160
180
Temperature (oC)
200
Figure 4.25: Temperature effect towards dibenzoylation of biphenyl over SCAL-4.
4.8.4
Effect of Catalyst Loading
Catalyst loading plays a vital role in enhancing the rate of conversion of
biphenyl to 4, 4’-DBBP. The effect of catalyst concentration is studied at 180 oC for
24 h of reaction over SCAL-4 as catalyst and the results are shown in Figure 4.26.
When the catalyst loading is increased, the amount of Brönsted acid active sites is
also increased and it leads to the increment of the reactant conversion. The results of
dibenzoylation reaction conducted are inline with the statement mentioned as above
where the conversion of biphenyl is also found to increase from 48.7% to 99.9% when
the catalyst loading is increased from 0.25 g to 0.75 g,. The amount of Brönsted acid
active sites is in sulphated AlMCM-41 with different loading is calculated and
perented in Table 4.9.
62
63
84.74
83.20
90
BP
4-PBP
4, 4'-DBBP
80
Concentration (%)
70
51.31
48.77
60
50
40
30
20
14.72
10.42
10
0.00
5.80
0.12
0
0.25
0.50
Catalyst Loading (g)
0.75
Figure 4.26: Effect of catalyst loading towards dibenzoylation of biphenyl over
SCAL-4.
Table 4.9: Amount of Brönsted acid active sites in SCAL-4 with different loading and
and its effect towards conversion of biphenyl.
Catalyst loading
Amount of Brönsted acid sites
Conversion of biphenyl
(g)
(µmol Pyridine g-1)
(%)
0.25
53.85
48.7
0.50
107.70
94.2
0.75
161.55
99.9
63
64
4.8.5
Effect of Biphenyl : Benzoyl Chloride Mole Ratio
The results of the influence biphenyl : benzoyl chloride mole ratios on the
biphenyl conversion towards the formation of 4-PBP and 4, 4’-DBBP at the
temperature of 180 oC are summarized in Figure 4.27. When benzoyl chloride is used
in large excess, the probability of multiple substitutions at the biphenyl are enhanced,
thus increases the formation of disubstituted product. Therefore, a use of high benzoyl
chloride in the reaction is a need to ensure the formation of the dibenzoylated product.
Besides that, the confined geometry in the pores can reduce the amount of ortho and
meta substituted product [5]. As a result, the formation of the para dibenzoylated
product is preferred. The conversion of biphenyl at 1 : 145, 1 : 290, 1 : 435 and 1 :
580 molar ratios of biphenyl to benzoyl chloride is found to be 62.1%, 55.2%, 31.0%
and 5.8%, respectively whereas the selectivity for 4- PBP and 4, 4’-DBBP increase
gradually as benzoyl chloride content increases.
83.20
90
80
Concentration (%)
70
65.07
62.12
55.15
60
44.81
50
40
BP
4-PBP
4, 4'-DBBP
37.22
31.03
30
20
10
3.06
0.00
0.00
5.80
11.00
0
1 : 145
1 : 290
1 : 435
1 : 580
Biphenyl : Benzoyl Chloride molar ratio
Figure 4.27: Effect of Biphenyl : Benzoyl Chloride molar ratio towards
dibenzoylation of biphenyl over SCAL-4.
64
65
4.9
Mechanism
From the results obtained, it can be observed that 4, 4’-DBBP was produced
after certain conversion (>90%) of Biphenyl (BP). This phenomenon is not only
related to the amount of BP and 4-PBP existed in the system but also electron density
factor in BP and 4-PBP. The electron density in 4-PBP is lower than BP due to
dislocation of electrons, leading to inactivity of 4-PBP in attacking benzoylium ion to
form disubstituted 4, 4’-DBBP. In contrast, BP with higher electron density tends to
attack benzoylium ion to form 4-PBP. However, 4-PBP becomes dominant in
attacking benzoylium ion when the concentration of BP is very low. Figure 4.28
demonstrates how BP and 4-PBP attacks benzoylium ion.
O
δ
δ
C
Biphenyl
δ
O
O
C
C
e4-Phenyl Benzophenone
Figure 4.28: Mechanism of how the electron density affects BP and 4-PBP in
attacking benzoylium ion.
The dibenzoylation of biphenyl involves electrophilic substitution. Figure 4.29
shows the schematic diagram of the catalytic cycle which is agreement with the data
reported. The figure suggests that the catalyst polarizes the benzoyl chloride molecule
into an electrophile (benzoylium ion) which then is attacked by the benzene ring of
biphenyl molecule resulting in the formation of 4-PBP. Further attack of 4-PBP
towards benzoylium ion via the same pathway finally gives 4, 4’-DBBP as shown in
Figure 4.30.
65
66
+OH
O
C
Cl + H-OSO3-AlMCM-41
Benzoyl chloride
(Excess)
Cl + -OSO3-AlMCM-41
Sulphated AlMCM-41
+OH
C
C
O
Cl
C
+ HCl
Benzoylium ion
O
O
C
C
H
-
OSO3-AlMCM-41
O
+ H-OSO3-AlMCM-41
C
4-PBP
Figure 4.29: Formation of 4-phenyl benzophenone (4-PBP) via electrophilic
substitution.
66
67
+
O
C
Cl + H-OSO3-AlMCM-41
Benzoyl chloride
(Excess)
C
Cl + -OSO3-AlMCM-41
Sulphated AlMCM-41
+OH
C
OH
O
Cl
C
+ HCl
Benzoylium ion
O
O
C
C
O
O
C
C
H
-
OSO3-AlMCM-41
O
O
C
C
+ H-OSO3-AlMCM-41
4, 4'-DBBP
Figure 4.30: Reaction mechanism of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP).
67
68
4.10
3
2
Mass balance of dibenzoylation of biphenyl with benzoyl chloride
1
2
O
C
Cl
Benzoyl Chloride
O
+ 3 HCl
2
C
4-PBP
+
+
BP
1
2
O
O
C
C
4, 4'-DBBP
Figure 4.31: Stoichiometrical equation of dibenzoylation of biphenyl reaction.
Figure 4.31 depicts the theoretical (stoichiometrical) chemical equation of
dibenzoylation of biphenyl reaction. This equation exhibits that 1 mole of biphenyl
(BP) reacts with 3/2 moles of benzoyl chloride to produce 1/2 mole of 4-phenyl
benzophenone (4-PBP), 1/2 mole of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP) and 3/2
moles of hydrogen chloride (HCl). The theoretical mass balance is described as in
Table 4.10 while its detailed calculations are depicted in APPENDIX M. This mass
balance considers the actual feeding of reactant in the experiment.
Table 4.11 shows the experimental mass balance of dibenzoylation of
biphenyl with benzoyl chloride reaction while the detailed calculations are shown in
APPENDIX N. From the data, it can be observed that the mass of products produced
in experiment are different with those calculated from theoretical one. This is because
the mass balance in theoretical one assumes that the BP is totally reacted and there
occurs no other side reaction such as hydrolysis of benzoyl chloride. Hydrolysis of
benzoyl chloride causes production of benzoic acid and benzoic anhydride as shown
in Figure 4.32. Apart from that, the calculation does not consider the presence of other
benzoylating agent such as benzoic acid and benzoic anhydride. Therefore, the figures
calculated from theory are different with those of experimental one. The products
quantity produced can also be affected by the presence of foreign molecules (for
example benzoic acid and benzoic anhydride) in the reaction. Such molecules may
activate or deactivate the reactants and hence affecting the amount of yield. In the
68
69
dibenzoylation reaction’s case, the amount of BP, 4-PBP and 4, 4’-DBBP calculated
from GC calibration technique is not equivalent and lower than the theoretical one.
Therefore, it may be influenced by the factors mentioned above. Many attempts had
been carried out in order to eliminate the moisture contact with benzoyl chloride,
including performing reaction under dried N2 gas condition. However, the efforts
were failed. The author could only minimize the moisture factor as much as possible.
Nevertheless, the calculations in both theoretical and experimental are balanced. They
do seem to follow the Law of Conservation of Mass where mass of reactant feeded in
is equivalent to mass of product produced in the reaction.
Table 4.10: Theoretical mass balance.
Substances
BP
In (mg)
Out (mg)
154.00
0.00
BOCl
12110.00
11899.25
4-PBP
0.00
129.00
4, 4’-DBBP
0.00
181.00
HCl
0.00
54.75
12264.00
12264.00
TOTAL
Table 4.11: Experimental mass balance.
Substances
BP
In (mg)
Out (mg)
154.00
8.93
BOCl
12110.00
4196.86
4-PBP
0.00
214.66
4, 4’-DBBP
0.00
37.72
HCl
0.00
2183.79
Benzoic acid
0.00
2597.24
Benzoic anhydride
0.00
3766.17
714.68
0.00
12978.68
13005.37
≈13000.00
≈13000.00
Moisture (H2O)
TOTAL
69
70
O
O
C
Cl
+
H
O
H
C
Cl + HO
C
Benzoyl chloride
+ HCl
Benzoic acid
Benzoyl chloride
O
OH
O
O
C
C
O
O
+ HCl
C
Benzoic anhydride
Benzoic acid
Figure 4.32: Hydrolysis of benzoyl chloride as side reaction in production of benzoic
acid and benzoic anhydrice.
4.10
Proposed Structure
After successfully synthesizing a novel sulphated mesoporous AlMCM-41
through sulphation and data interpretation, thestructure of the sulphated aluminium
species can be proposed. The proposed structure to the sulphated materials is shown in
Figure 4.33 after considering all the information and interpretation obtained from
characterization techniques. The scheme considers that the material surface is totally
dehydrated, which is obtained after activation at 200 oC, with the sulphate covalently
bonded to the aluminium and silicon via oxygen atoms. The negative charge of the
complex is neutralized and balanced by H+ cation.
3H+
OAl(OSO3H)533H+
Si
3-(HO SO) AlO
3
5
3H+
OAl(OSO3H)53-
(HO3SO)5AlO
3H+
O
3H+
3-(HO SO) AlO
3
5
OAl(OSO3H)53O
Si
Cl
OAl(OSO3H)533H+
3H+
3-
Al2(SO4)3
Si
OAl(OSO3H)533H+
3H+
OAl(OSO3H)53-
Si
3H+
OAl(OSO3H)53-
OSO3H
Si
Si
O
O
O
Si
Si
Si Si
O
O
O
Si
Si Si
O
O
Si
MCM-41 surface
Figure 4.33: Scheme proposed for the sulphated AlMCM-41 materials showing
possible Brönsted acid sites.
70
71
CHAPTER 5
CONCLUSIONS
5.1
Conclusions
The study has demonstrated that sulphated AlMCM-41 molecular sieves is an
active catalyst for dibenzoylation of biphenyl. The study also implies that physical
properties of this catalyst such as degree of crystallinity and crystallite size strongly
depend on Al2O3 content, temperature of calcination and techniques of modification.
From acidity studies, sulphated molecular sieve SCAL-4 with SiO2/Al2O3 ratio = 15
contains the highest amount of Brönsted acid sites and the acidity amount decreased
as the aluminium content reduced.
27
Al MAS NMR indicates the presence of
octahedrally coordinated extra-framework sulphated aluminiums (EFAL) which
contributes to the Brönsted acidity of the system. It was demonstrated that aluminium
from the framework migrated to the surface upon sulphation to form Brönsted acid
sites. Evidently, the acid strength of the sulphated MCM-41 materials are stronger
than sulphuric acid and H-AlMCM-41.
Results from this work demonstrate that all sulphated MCM-41 samples are
solid Brönsted acid with high surface area (>500 m2/g) and active towards
benzoylation and dibenzoylation of biphenyl. The production of 4, 4’-DBBP is
affected by the acid strength, amount of acid site, amount of biphenyl and 4-PBP,
temperature, catalyst loading and duration of the reaction. Sulphated SCAL-4 catalyst
gave the highest conversion of biphenyl over H-AlMCM-41, sulphuric acid and
sulphated amorphous silica. SCAL-4 was also found to be the most active catalyst
towards dibenzoylation of biphenyl, giving 11.0% yield of 4, 4’-DBBP.
71
72
The proposed mechanism of heterogeneous catalysis of dibenzoylation of
biphenyl involves electrophilic aromatic substitution and formation of acylium ions
from the Brönsted acid sites in the catalysts. The results suggest that dibenzoylation of
biphenyl is a consecutive reaction (route 2 shown in Figure 1.1) where the conversion
of 4, 4’-DBBP is via the formation of 4-PBP.
72
73
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78
79
APPENDIX A
Calculation of the amount of pyridine adsorbed on the sample in the acidity study of
sulphated AlMCM-41 samples.
The general formula to obtain the amount of pyridine in µmole per gram sample:
Adsorbed pyridine (µmole. g-1) =
B (cm-1) . Sample surface (cm2)
Adsorption Coef. (cm. µmole-1). Weight (g)
Where B (band area) = Imax ×∆½
Where Imax is the intensity of the band (in absorbance unit) and ∆½ half width at half
height.
For a pellet that is 13 mm in diameter and 10 mg in weight, the sample surface that is
transversed by the radiation is 0.7857 cm (from only 10 mm exposed to the IR
radiation) on a 5.92 mg sample. The adsorption coefficient values are taken from the
literature [53] where
Brönsted = 3.03 ± 0.01
Lewis = 3.80 ± 0.01
Therefore, for the samples used in this study which were prepared from 10 mm
diameter pellet and 10 mg sample in which the area transversed by the radiation and
its respective weight are 0.7857 cm2 and 5.92 × 10-3 g respectively, the amount of
pyridine adsorbed (in µmole) is calculated according to the following:
Brönsted acidity = B (cm-1) × 43.80 (cm. µmole g-1)
Lewis acidity = B (cm-1) × 34.92 (cm. µmole g-1)
The area of the band is determined by means of the computer program of the FTIR
instrument.
79
80
APPENDIX B
Infrared spectrum of 4-phenyl benzophenone (4-PBP).
56.6
800.89
50
453.69
45
1000.64
1483.19
40
3048.02
1073.32
1150.39
C-H aromatic
1443.67
1399.22
35
632.84
934.58
850.66
%T 30
760.52
730.06
25
1597.83
20
1287.92
C=C
aromatic
15
10
C=O
7.0
4000.0
690.72
1642.79
3000
2000
1500
1000
400.0
cm-1
80
81
APPENDIX C
Mass spectrum of 4-phenyl benzophenone (4-PBP).
Abundance
Mass spectrum of 4-PBP
500000
181
450000
258
400000
350000
300000
250000
200000
152
150000
100000
77
105
50000
51
0
40
127
60
80
100
120
230
202
140
160
180
200
220
240
260
281
280
300
320
341
340
360
380
405
400 m/z
81
82
APPENDIX D
Infrared spectrum of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP).
64.9
60
55
50
3053.75
1180.92
1550.50
1443.14
C-H aromatic
45
997.74
977.92
451.74
1148.07
1075.32
1393.40
40
640.72
787.13
933.14
734.52
840.60
1312.63
35
%T 30
1601.29
25
693.58
20
C=C
aromatic
15
1286.50
10
1645.11
5
C=O
0.0
4000.0
3000
2000
cm-1 cm-1
1500
1000
400.0
82
83
APPENDIX E
Mass spectrum of 4, 4’-dibenzoyl biphenyl (4, 4’-DBBP).
Abundance
Mass Spectrum of 4, 4’-DBBP
3000000
285
362
2800000
2600000
2400000
2200000
2000000
1800000
1600000
105
1400000
1200000
1000000
77
800000
600000
400000
152
200000
51
180
126
202
0
50
100
150
200
226
257
313
250
300
334
383
350
405
400
429
479
450
503
500 m/z
83
84
APPENDIX F
Calculation of % conversion and % selectivity.
Conversion (%)
=
Amount of biphenyl reacted
Amount of biphenyl input
Selectivity (%)
=
Peak area of desired product
Total peak area of all products
× 100%
× 100%
84
85
APPENDIX G
The pyridine-FTIR spectra of HCAL-1 at (a) room temperature, (b) 150 oC, (c) 250 oC
and (d) 350 oC.
B
L
(d)
(c)
(b)
A
(a)
1640 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400
cm-1
85
86
APPENDIX H
The pyridine-FTIR spectra of HCAL-2 at (a) room temperature, (b) 150 oC, (c) 250 oC
and (d) 350 oC.
B
L
(d)
(c)
(b)
A
(a)
1640 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400
cm-1
86
87
APPENDIX I
The pyridine-FTIR spectra of HCAL-3 at (a) room temperature, (b) 150 oC, (c) 250 oC
and (d) 350 oC.
B
L
(d)
(c)
(b)
A
(a)
1640 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400
cm-1
87
88
APPENDIX J
The pyridine-FTIR spectra of HCAL-4 at (a) room temperature, (b) 150 oC, (c) 250 oC
and (d) 350 oC.
B
L
(d)
(c)
(b)
A
(a)
1640 1620 1600 1580 1560 1540 1520 1500 1480 1460 1440 1420 1400.0
cm-1
88
89
APPENDIX K
Chromatogram of reactants at 0 h.
♣
♦
♠
Notes :
♣= Solvent
™
♦= Benzoyl chloride
♠= Biphenyl
™= Hexadecane
89
90
APPENDIX L
Chromatogram of reactants and products.
♣
♦

Notes :
♥
Ö
™
♣= Solvent,
♦ = Benzoyl chloride
♥ = Benzoic acid
♠ = Biphenyl
™ = Hexadecane
 = Benzoic anhydride
Ö = 4-Phenyl Benzophenone
³ = 4, 4’-Dibenzoyl biphenyl
♠
³
90
91
APPENDIX M
Data obtained from GC-FID Chromatograms (Friedel-Crafts dibenzoylation of biphenyl with benzoyl chloride over SCAL-4).
Rt
Duration of time (h)
9.72 Biphenyl area
0
1
8
45645387 38665234 29666633 17358401
17.78 4-PBP area
0
30.33 4, 4’-DBBP area
0
11.72 Internal standard area
3
17
20
24
28
32
4331111
2274785
1939926
2305477
1886636
7531918 14491535 24269132 32237499 25860161 27933625 33536006 30878456
0
0
327100
664017
14054210 14214820 13578680 12944210 11496140
837243
2044387
2629563
2501436
9095025 10296583 12451465 11548641
Conversion, %
0
16.25
32.73
58.71
88.40
92.30
94.20
94.30
94.97
Selectivity of 4-PBP, %
0
16.30
32.82
57.85
86.58
89.26
87.52
87.17
87.56
Selectivity of 4-DBBP, %
0
0
0
0.78
1.78
2.89
6.41
6.84
7.09
Duration of time (h)
0
1
3
8
17
100.00
83.75
67.27
41.29
11.60
% 4-PBP
0
16.25
32.73
57.50
% 4, 4’-DBBP
0
0
0
1.40
% Biphenyl
20
24
28
32
7.70
5.80
5.70
5.03
86.00
87.20 83.20
82.60
82.00
3.20
5.10 11.00
11.70
12.00
91
92
APPENDIX N
Mass balance of dibenzoylation of biphenyl with benzoyl chloride (Experimental)
O
+
C
HCl
4-PBP
+
BP
O
O
+
C
C
O
C
4, 4'-DBBP
Cl
+
Benzoyl Chloride
C
O
O
O
OH
+
+
C
Benzoic acid
C
O
Benzoic anhydride
H2O
O
+
BP
C
Benzoyl Chloride
Basis: 1 mmol of BP ≡ 24 h of operation at 180 oC
Reactants feeded :
BP
= 1 mmol
= 1 mmol × 154 g.mol −1 × 1000 mol.mmol −1 × 1000 mg.g −1
= 154.00 mg
BOCl = 10 ml × 1.211 g.ml −1 × 1000 mg.g −1
= 12110.00 mg
Vapour in reaction
= w mg
Cl
93
Products formed :
4-PBP = 83.2% × 1 mmol × 258 g.mol −1
= 214.66 mg
4, 4’-DBBP = 10.4% × 1 mmol × 362 g .mol −1 × 1000 mg.g −1 ×
1 mol
1000 mmol
= 37.65 mg
Benzoic acid = 2.90358 g × 1000 mg.g −1
= 2903.58 mg
HCl
= x mg
Reactants unreacted :
BP
= 5.8% × 1 mmol × 154 g.mol −1 × 1000 mg.g −1 ×
= 8.93 mg
BOCl = y mg
Benzoic anhydride
= z mg
Carbon atom
Mass of C atoms in BP feeded :
⎤
⎡12 g .mol −1 × 12
⎢
=
× 154 mg ⎥
⎥
⎢ 154 g .mol −1
⎦
⎣
= 144 mg
Mass of C atoms in BOCl feeded :
⎡12 g.mol −1 × 7
⎤
⎥
= ⎢
×
12110
mg
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 7240.14 mg
Mass of C atoms in 4-PBP produced :
⎡12 g.mol −1 × 19
⎤
⎥
= ⎢
×
214
.
66
mg
⎢ 258 g.mol −1
⎥
⎣
⎦
= 189.70 mg
1 mol
1000 mmol
94
Mass of C atoms in 4, 4’-DBBP produced :
⎡12 g.mol −1 × 26
⎤
⎥
37
.
65
mg
= ⎢
×
⎢ 362 g.mol −1
⎥
⎣
⎦
= 32.51 mg
Mass of C atoms in benzoic acid produced :
⎡12 g.mol −1 × 7
⎤
⎥
2597
.
24
mg
= ⎢
×
⎢ 122 g.mol −1
⎥
⎣
⎦
= 1788.26 mg
Mass of C atoms in BP unreacted :
⎡12 g.mol −1 × 12
⎤
⎥
= ⎢
×
8
.
932
mg
⎢ 154 g.mol −1
⎥
⎣
⎦
= 8.35 mg
Mass of C atoms in BOCl unreacted :
⎡12 g.mol −1 × 7
⎤
⎢
=
× y mg ⎥
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 0.60 y mg
Mass of C atoms in benzoic anhydride produced :
⎡12 g.mol −1 × 14
⎤
⎥
z
mg
= ⎢
×
⎢ 226 g.mol −1
⎥
⎣
⎦
= 0.74 z mg
∴Mass of C atoms in = Mass of C atoms out
Mass of C atoms in (BP feeded + BOCl feeded) = Mass of C atoms in (4-PBP
produced + 4, 4’-DBBP produced + BP unreacted + BOCl unreacted + benzoic acid
produced + benzoic anhydride produced)
(144
)
(
)
+ 7240.14 mg = 189.70 + 32.51 + 8.35 + 0.60 y + 1788.26 + 0.74 z mg
⇒ 5365.38 mg = 0.60 y mg + 0.74 z mg
------------------1
95
H atom
Mass of H atoms in BP feeded :
⎤
⎡1 g.mol −1 × 10
⎢
=
× 154 mg ⎥
⎥
⎢ 154 g.mol −1
⎦
⎣
= 10 mg
Mass of H atoms in BOCl feeded :
⎤
⎡1 g.mol −1 × 5
⎥
12110
mg
= ⎢
×
⎥
⎢ 140.5 g .mol −1
⎦
⎣
= 430.96 mg
Mass of H atoms in H2O (vapour) feeded :
⎤
⎡1 g.mol −1 × 2
⎥
w
mg
= ⎢
×
⎥
⎢ 18 g.mol −1
⎦
⎣
= 0.11w mg
Mass of H atoms in 4-PBP produced :
⎡1 g.mol −1 × 14
⎤
⎥
214
.
66
mg
= ⎢
×
⎢ 258 g.mol −1
⎥
⎣
⎦
= 11.65 mg
Mass of H atoms in 4, 4’-DBBP produced :
⎡1 g.mol −1 × 18
⎤
⎥
mg
37
.
72
= ⎢
×
⎢ 362 g.mol −1
⎥
⎣
⎦
= 1.88 mg
Mass of H atoms in benzoic acid produced :
⎤
⎡1 g.mol −1 × 6
⎥
2597
.
24
mg
= ⎢
×
⎥
⎢ 122 g.mol −1
⎦
⎣
= 127.73 mg
96
Mass of H atoms in BP unreacted :
⎡1 g.mol −1 × 10
⎤
⎥
mg
8
.
93
= ⎢
×
⎢ 154 g.mol −1
⎥
⎣
⎦
= 0.58 mg
Mass of H atoms in HCl produced :
⎤
⎡1 g .mol −1 × 1
⎥
x
mg
= ⎢
×
⎥
⎢ 36.5 g.mol −1
⎦
⎣
= 0.03 x mg
Mass of H atoms in BOCl unreacted :
⎡1 g.mol −1 × 5
⎤
⎥
y
mg
= ⎢
×
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 0.04 y mg
Mass of H atoms in benzoic anhydride produced :
⎡1 g.mol −1 × 10
⎤
⎢
=
× z mg ⎥
⎢ 226 g.mol −1
⎥
⎣
⎦
= 0.04 z mg
∴Mass of H atoms in = Mass of H atoms out
Mass of H atoms in (BP feeded + BOCl feeded) = Mass of H atoms in (H2O + 4-PBP
produced + 4, 4’-DBBP produced + BP unreacted + HCl produced + BOCl unreacted
+ benzoic acid produced benzoic anhydride produced)
(10
⎛11.65 + 1.88 + 127.73
⎞
⎟mg
+ 430.96 mg = ⎜⎜
⎟
0
.
58
0
.
11
0
.
03
0
.
04
0
.
04
+
+
+
+
+
w
x
y
z
⎝
⎠
)
⇒ 320.42 mg = 0.11w + 0.03 x mg + 0.40 y mg + 0.04 z mg
-----------2
97
O atom
Mass of O atoms in BOCl feeded :
⎡16 g.mol −1 × 1
⎤
⎥
12110
mg
= ⎢
×
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 1379.07 mg
Mass of O atom in vapour (H2O) :
⎡16 g.mol −1 × 1
⎤
⎥
w
mg
= ⎢
×
⎢ 18 g.mol −1
⎥
⎣
⎦
= 0.89w mg
Mass of O atoms in 4-PBP produced :
⎡16 g.mol −1 × 1
⎤
⎥
= ⎢
×
214
.
66
mg
⎢ 258 g.mol −1
⎥
⎣
⎦
= 13.31 mg
Mass of O atoms in 4, 4’-DBBP produced :
⎡16 g.mol −1 × 2
⎤
⎥
37
.
72
mg
= ⎢
×
⎢ 362 g .mol −1
⎥
⎣
⎦
= 3.33 mg
Mass of O atoms in benzoic acid produced :
⎡16 g.mol −1 × 2
⎤
⎥
2597
.
24
mg
= ⎢
×
⎢ 122 g.mol −1
⎥
⎣
⎦
= 681.24 mg
Mass of O atoms in BOCl unreacted :
⎡16 g.mol −1 × 1
⎤
⎥
= ⎢
×
y
mg
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 0.11y mg
Mass of O atoms in benzoic anhydride produced :
⎡16 g.mol −1 × 3
⎤
⎥
= ⎢
×
z
mg
⎢ 226 g.mol −1
⎥
⎣
⎦
= 0.21z mg
98
∴Mass of O atoms in = Mass of O atoms out
Mass of O atoms in (BOCl feeded + H2O) = Mass of O atoms in (4-PBP produced +
4, 4’-DBBP produced + BOCl unreacted + benzoic acid produced + benzoic
anhydride produced)
(1397.07
)
(
)
+ 0.89w mg = 13.31 + 3.33 + 681.24 + 0.11y + 0.21z mg
⇒ 681.20 mg = 0.11y mg + 0.21z mg − 0.89w
--------------------3
Cl atom
Mass of Cl atoms in BOCl feeded :
⎡ 35.5 g .mol −1 × 1
⎤
⎥
12110
mg
= ⎢
×
⎢ 140.5 g .mol −1
⎥
⎣
⎦
= 3059.82 mg
Mass of Cl atoms in HCl produced :
⎡ 35.5 g .mol −1 × 1
⎤
⎥
x
mg
= ⎢
×
⎢ 36.5 g .mol −1
⎥
⎣
⎦
= 0.97 x mg
Mass of Cl atoms in BOCl unreacted :
⎡ 35.5 g.mol −1 × 1
⎤
⎥
= ⎢
×
y
mg
⎢ 140.5 g.mol −1
⎥
⎣
⎦
= 0.25 y mg
∴Mass of Cl atom in = Mass of Cl atom out
Mass of Cl atom in BOCl feeded = Mass of Cl atom in (BOCl unreacted + HCl
produced)
⇒ 3059.82 mg = (0.97 x + 0.25 y )mg
------------------4
99
By solving the equations above,
w = 714.68, x = 3766.17mg, y = 4196.86mg, z = 2183.79mg
The Law of Conservation of Mass states that,
{Mass in}
Substances
=
{Mass out}
In (mg)
Out (mg)
154.00
8.93
BOCl
12110.00
4196.86
4-PBP
–
214.66
4, 4’-DBBP
–
37.72
HCl
–
2183.79
Benzoic acid
–
2597.24
Benzoic anhydride
–
3766.17
714.68
–
12978.68
13005.37
BP
Moisture (H2O)
TOTAL
% error =
13005.37 − 12978.68
× 100%
13005.37
= 0.21%
100
APPENDIX O
Mass balance of dibenzoylation of biphenyl with benzoyl chloride (Theoretical)
3
2
1
2
O
C
Cl
O
4-PBP
+
Benzoyl Chloride
+ 3 HCl
2
C
+
BP
1
2
O
O
C
C
4, 4'-DBBP
Basis: 1 mmol of BP ≡ 24 h of operation at 180 oC
Reactants feeded :
BP
= 1 mmol
= 1 mmol × 154 g.mol −1 × 1000 mol.mmol −1 × 1000 mg.g −1
= 154.00 mg
BOCl = 10 ml × 1.211 g.ml −1 × 1000 mg.g −1
= 12110.00 mg
Products formed :
1
mmol × 258 g.mol −1
4-PBP =
2
= 129.00 mg
1
mmol × 362 g.mol −1
2
= 181.00 mg
4, 4’-DBBP =
3
mmol × 36.5 g.mol −1
2
= 54.75 mg
HCl =
101
Reactants unreacted :
⎛
3
⎡
⎤⎞
BP
= ⎜⎜12100.00 mg − ⎢140.5 g .mol −1 ×
mmol ⎥ ⎟⎟
2
⎣
⎦⎠
⎝
= 11899.25 mg
The Law of Conservation of Mass states that,
{Mass in}
Substances
BP
In (mg)
=
{Mass out}
Out (mg)
154.00
0.00
BOCl
12110.00
11899.25
4-PBP
0.00
129.00
4, 4’-DBBP
0.00
181.00
HCl
0.00
54.75
12264.00
12264.00
TOTAL