OPTIMIZATION OF MODIFIED SOL-GEL METHOD FOR THE
FORMATION OF TETRAGONAL PHASE ZIRCONIA IN Zr(IV)/Ce(IV)
CATALYST
LEIW SOOK FUN
UNIVERSITI TEKNOLOGI MALAYSIA
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS
JUDUL : OPTIMIZATION OF MODIFIED SOL-GEL METHOD FOR THE
FORMATION OF TETRAGONAL PHASE ZIRCONIA IN Zr(IV)/Ce(IV)
CATALYST
SESI PENGAJIAN : 2004/2005
Saya :
LEIW SOOK FUN
(HURUF BESAR)
mengaku membenarkan tesis ini disimpan di Perpustakaan Universiti Teknologi Malayisa dengan
syarat-syarat seperti berikut :
1. Hakmilik tesis ini adalah dibawah nama penulis melainkan penulisan sebagai projek bersama
dan dibiayai oleh UTM, hakmiliknya adalah kepunyaan UTM.
2. Naskah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenaran
bertulis daripada penulis.
3. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan
pengajian mereka.
4. Tesis hanya boleh diterbitkan dengan kebenaran penulis. Bayaran royalti adalah mengikut
kadar yang dipersetujui kelak.
5. *Saya membenarkan / tidak membenarkan Perpustakaan membuat salinan tesis ini sebagai
bahan pertukaran di antara institusi pengajian tinggi.
6. **Sila tandakan (— )
SULIT
TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau
kepentingan Malaysia seperti yang termaktub di dalam
AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi / badan di mana penyelidikan dijalankan)
TIDAK TERHAD
—
(TANDATANGAN PENULIS)
(TANDATANGAN PENYELIA)
Alamat Tetap : NO.E-49 BATU DUA,
33300 GERIK, PERAK.
PM. DR. NOR AZIAH BUANG
(NAMA PENYELIA)
Tarikh
Tarikh :
:
CATATAN : * Potong yang tidak berkenaan.
** Jika Tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak
berkuasa / organisasi berkenaan dengan menyatakan sekali tempoh tesis
ini perlu dikelaskan sebagai SULIT atau TERHAD.
“Saya/kami* akui bahawa saya/kami* telah membaca karya ini dan pada pandangan
saya/kami* karya ini adalah memadai dari segi skop dan kualiti untuk tujuan
penganugerahan Ijazah Sarjana Muda/ Sarjana/ Doktor Falsafah Sains (Kimia).”
*
Tandatangan
: ..................................................
Nama Penyelia
: P. M. Dr. NOR AZIAH BUANG
Tarikh
: ………………………………..
Potong yang tidak berkenaan.
BAHAGIAN A  Pengesahan Kerjasama*
Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui
kerjasama antara _______________________ dengan ________________________
Disahkan oleh:
Tandatangan : _________________________________ Tarikh: ______________
Nama
: _________________________________
Jawatan
: _________________________________
(Cop rasmi)
* Jika penyediaan tesis/projek melibatkan kerjasama.
BAHAGIAN B  Untuk Kegunaan Pejabat Sekolah Pengajian Siswajah
Tesis ini telah diperiksa dan diakui oleh:
Nama dan Alamat Pemeriksa Dalam : Prof. Dr. Wan Azelee bin Wan Abu Bakar
Jabatan Kimia, Fakulti Sains,
Universiti Teknologi Malaysia,
81300, Skudai Johor.
Nama dan Alamat Pemeriksa Dalam : Prof. Madya Dr. Zainab binti Ramli
Jabatan Kimia, Fakulti Sains,
Universiti Teknologi Malaysia
81300, Skudai Johor.
Nama Penyelia Lain (jika ada)
: _____________________________________
_____________________________________
_____________________________________
Disahkan oleh Penolong Pendaftar di SPS:
Tandatangan : _________________________________ Tarikh: ______________
Nama
: _________________________________
OPTIMIZATION OF MODIFIED SOL-GEL METHOD FOR THE
FORMATION OF TETRAGONAL PHASE ZIRCONIA IN Zr(IV)/Ce(IV)
CATALYST
LEIW SOOK FUN
A dissertation submitted in partial fulfillment of the requirements for the award
of the degree of Master of Science (Chemistry)
Faculty of Science
Universiti Teknologi Malaysia
MARCH, 2005
ii
³I deFlare that this dissertation is the results oI my own researFh e[Fept as in Fited
reIerenFes. The dissertation has not been aFFepted Ior any degree and is not
FonFurrently submitted in Fandidature oI any degree.´
Signature
: ..................................................
Name oI Candidate
: LEI: S22K )UN
Date
: ««««««««««««..
iii
This dissertation is dediFated to my beloved Iamily and Choong Meng
Thanks Ior being there when I needed you.
iv
ACKNOWLEDGEMENTS
I would like to e[press my deepest and sinFere thanks to my projeFt
supervisor, AssoFiate ProIessor Dr. Nor A]iah Buang Ior valuable ideas and helpIul
guidanFe given sinFe the beginning oI this researFh.
SinFere gratitude also goes to all those who have helped me direFtly or
indireFtly in this researFh, ProIessor Dr. :an A]elee :an Abu Bakar, Mrs. Mariam
Hassan, Mr. Hanan, Mr. A]mi, and Mr. Junaidi Bin Mohamad Nasir Irom the
Department oI Chemistry, Mr. JaaIar Raji Irom the Department oI PhysiFs,
Mr. =ainal Abidin Abbas and Mr. JeIri Irom the )aFulty oI MeFhaniFal Engineering.
Thanks are also due to Mr. Lim Kheng :ei Irom the Institute Ibnu Sina Ior an easy
aFFess to ;RD analytiFal instrument.
)inally, I am grateIul Ior the motivation and support oI my Iamily and Iriends
in Fompleting my thesis projeFt. Thank you Ior your support and Iaith in me and Ior
making it all worthwhile.
v
ABSTRACT
=irFonium-Ferium mi[ed metal o[ides is widely used as promoters in
automobile emissions Fontrol Fatalyst systems (Three-:ay Catalyst, T:C). In order
to improve the perIormanFe oI ]irFonia-Feria Fatalysts, a researFh has been done to
develop a ]irFonia-based Fatalyst doped with Feria by modiIied sol-gel method with
]irFonium o[yFhloride and Ferium (III) nitrate he[ahydrate as the preFursors. This
researFh investigated the optimum Fonditions on the Iormation oI single phase
tetragonal =r22. A series oI =r1-[Ce[22 Fatalyst by varying the atomiF perFentage
ratios were prepared in diIIerent amount oI water and FalFinations temperature. The
properties oI Fatalysts were FharaFteri]ed with ;-Ray DiIIraFtion (;RD), surIaFe
area analysis, and )ourier-TransIorm InIrared SpeFtrosFopy ()TIR). The Fatalyst
showed the best result is seleFted to test Ior C2 Fonversion. The =r.7Ce.322
Fatalyst prepared in 5 mL oI water dried Ior two days at 7 žC and FalFined at 4 žC
Ior 17 hours gives the optimum Fondition on the highest Iormation oI single phase
tetragonal =r22. The ;RD analysis showed that this Fatalyst has Frystallinity
property, Fonsists oI tetragonal =r22 as the main phase and average Frystallite si]e oI
appro[imately 12.9 nm serve as the aFtive phases Ior the Fatalyst. SurIaFe area
analysis showed that this Fatalyst has 35.36 m2/g oI surIaFe area. The )TIR analysis
showed the e[istenFe oI surIaFe hydro[yl group on the surIaFe oI Fatalyst. The
bands that were assigned to the water deIormation mode and hydro[yl deIormation
mode oI surIaFe hydro[yl groups have been eliminated as the FalFination temperature
inFreased. The =r.7Ce.322 Fatalyst prepared in 5 mL oI water was reported to
e[hibit the best FatalytiF aFtivity towards C2 Fonversion, it showed the lowest TL2 at
room temperature while 1 C2 Fonversion was aFhieved at T1
32 žC.
vi
ABSTRAK
Campuran logam oksida ]irkonium-Ferium diguna seFara meluas sebagai
penyokong dalam sistem pemangkinan bagi pengawalan bahan penFemar daripada
kenderaan bermotor (Pemangkinan Tiga Arah, TWC). Demi meningkatkan
keupayaan mangkin ]irkonia-Feria, satu kajian telah dilakukan untuk menyediakan
mangkin berasaskan ]irkonia yang didopkan dengan Feria melalui kaedah
pengubahsuaian sol-gel di mana ]irkonium oksiklorida dan Ferium (III) nitrat
heksahidrat sebagai bahan pemula. Kajian ini dijalankan bertujuan menyelidik
keadaan yang optimum bagi pembentukan Iasa tunggal =r22 berstruktur tetragonal.
Satu siri mangkin =r1-[Ce[22 telah disediakan dengan mempelbagaikan nisbah
peratus atom dan menggunakan kuantiti air serta suhu pengkalsinan yang berbe]a.
Analisis penFirian dilakukan terhadap mangkin dengan menggunakan teknik
pembelauan sinar-; (;RD), analisis luas permukaan dan )TIR. Mangkin yang
menunjukkan keputusan yang terbaik dipilih untuk kajian penukaran gas karbon
monoksida (C2) kepada C22. Mangkin =r.7Ce.322 yang disediakan
menggunakan 5 mL air dan dikering pada suhu 7 žC selama dua hari serta dikalsin
pada suhu 4 žC selam 17 jam menunjukkan keadaan yang paling optimum dalam
pembentukan Iasa tunggal =r22 berstruktur tetragonal. Analisis ;RD menunjukkan
mangkin ini terdiri daripada Iasa tetragonal =r22 sebagai Iasa utama dengan siIat
hablur serta purata sai] hablur kira-kira 12.9 nm yang bertindak sebagai Iasa aktiI
mangkin. Analisis luas permukaan menunjukkan mangkin ini mempunyai luas
permukaan sebanyak 35.36 m2/g. Keputusan )TIR menunjukkan kehadiran hidroksil
pada permukaan mangkin. PunFak-punFak bagi air, hidroksil telah disingkirkan
apabila suhu pengkalsinan meningkat. Penyediaan mangkin =r.7Ce.322 dalam
5 mL air memberikan keputusan aktiviti pemangkinan terhadap penukaran gas C2
yang paling baik di mana menunjukkan TL2 yang paling rendah pada suhu bilik
sementara 1 penukaran gas C2 diFapai pada T1
32 žC.
vii
CONTENTS
PAGE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
CONTENTS
vii
LIST OF TABLES
[
LIST OF FIGURES
[i
LIST OF SYMBOLS / ABBREVIATIONS /
NOTATIONS / TERMS
[iii
LIST OF APPENDICES
[iv
CHAPTER I
INTRODUCTION
1.1
Air Pollution
1
1.2
DeIinition and Types oI Pollutants
2
1.3
EIIeFts oI Air Pollution
2
1.4
Catalyst
3
1.5
CatalytiF Converter
3
1.6
Three-:ay Catalysts
4
1.7
=irFonium 2[ide or =irFonia
5
viii
1.
Cerium 2[ide or Ceria
7
1..1
9
Role oI Ce22 in the T:Cs
1.9
Catalysis by =irFonia-Ceria
9
1.1
Sol-Gel Chemistry
11
1.1.1 The Advantages oI Sol-Gel
ApproaFh 2ver the Traditional
Methods oI Preparation
14
1.1.2 EIIeFts oI 9ariables on the
Chemistry oI the Sol-Gel Synthesis
15
1.1.3 Preparation oI Catalysts by Sol-Gel
Method
1.11
16
Statement oI the Problem and the Needs oI
the Study
1
1.12
ResearFh 2bjeFtives
19
1.13
SFope oI ResearFh
19
CHAPTER II
EXPERIMENTAL
2.1
ChemiFals
2
2.2
E[periment
2
2.3
Preparation oI =irFonia Based Catalysts
Doped with Ceria by ModiIied Sol-Gel
Method
21
2.4
Drying and CalFination
22
2.5
CharaFteri]ation TeFhiniTues
23
2.5.1
;-Ray DiIIraFtion (;RD)
23
2.5.2
SurIaFe Area Analysis
25
2.5.3
)ourier-TranIorm InIrared
SpeFtrosFopy ()TIR)
2.6
CatalytiF AFtivity Testing Measurement
26
2
i[
CHAPTER III
3.1
RESULTS AND DISCUSSIONS
InIluenFe oI 9ariables on the )ormation oI
Tetragonal Phase =r22
3.1.1
3
EIIeFt oI Amount oI :ater on the
)ormation oI Tetragonal Phase
=r22-Based Catalyst Doped with
Ce22 (=r.95:Ce.5)
3.1.2
EIIeFt oI Loading oI Ce22 on the
)ormation oI Tetragonal Phase =r22
3.1.3
31
34
EIIeFt oI CalFination Temperature
on the )ormation oI Tetragonal Phase
=r22 in =r.7Ce.322 Catalyst
4
3.2
)ourier TransIorm InIrared ()TIR) Analysis
46
3.3
CatalytiF AFtivity oI =r.7Ce.322 Catalyst
Towards Carbon Mono[ide 2[idation
ReaFtion
CHAPTER IV
49
CONCLUSIONS
4.1
ConFlusions
52
4.2
)uture :orks
53
REFERENCES
55
APPENDICES
64
[
LIST OF TABLES
TABLE NUMBER
TITLE
PAGE
1.1
ReaFtions oFFurring on automobile e[haust Fatalyst
5
2.1
ClassiIiFation oI InIrared Radiation
27
3.1
;RD peaks assignment Ior =r.95Ce.522 Fatalyst
sample in diIIerent amount oI water
3.2
;RD peaks assignment Ior =r[Ce1-[22 Fatalyst
in mL oI water
3.3
36
;RD peaks assignment Ior =r[Ce[-122 Fatalysts
in 5 mL oI water
3.4
33
39
PartiFle si]es oI the sample with diIIerent amount
oI Feria perFentage in 5 mL and mL oI water
FalFined at 4 žC
3.5
4
;RD peaks assignment Ior =r.7Ce.322 Fatalyst
prepared in 5 mL and mL oI water FalFined at
4 žC and 6 žC
3.6
44
PartiFle si]es and surIaFe areas oI =r.7Ce.322
Fatalysts prepared in 5 mL and mL oI water
FalFined at 4 žC and 6 žC
3.7
46
CatalytiF aFtivity oI =r.7Ce.322 Fatalyst
towards C2 Fonversion
5
[i
LIST OF FIGURES
FIGURE NUMBER
TITLE
1.1
Diagram oI a typiFal FatalytiF Fonverter
2.1
SFhematiF diagram oI the Fatalyst preparation
PAGE
4
set-up using modiIied sol-gel method
21
2.2
BasiF Ieatures oI a typiFal ;RD e[periment
24
2.3
SFhematiF diagram oI the miFroreaFtor sample tube
29
3.1
DiIIraFtograms oI =r.95Ce.522 using diIIerent
amount oI water: (a) mL and (b) 5 mL
3.2
32
DiIIraFtograms oI =r[Ce1-[22 Fatalyst with diIIerent
amount oI Feria in mL oI water (a) =r.95Ce.522,
(b) =r.9Ce.122, (F) =r.Ce.222, and
(d) =r.7Ce.322
3.3
35
DiIIraFtograms oI =r[Ce1-[22 Fatalyst with diIIerent
amount oI Feria in 5 mL oI water (a) =r.95Ce.522,
(b) =r.9Ce.122, (F) =r.Ce.222, and
(d) =r.7Ce.322
3.4
3
DiIIraFtograms oI =r.7Ce.322 prepared using
5 mL oI water dried at (a) 7 žC, and FalFined at
(b) 4 žC and (F) 6 žC
3.5
42
DiIIraFtograms oI =r.7Ce.322 prepared using
mL oI water and FalFined at (a) 4 žC and
(b) 6 žC
3.6
43
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared
in 5 mL oI water dried at 7 žC
47
[ii
3.7
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared
in 5 mL oI water FalFined at 4 žC
3.
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared
in 5 mL oI water FalFined at 6 žC
3.9
4
49
PerFentage Fonversion oI C2 versus temperature
Ior the =r.7Ce.322 Fatalyst prepared in
mL and 5 mL oI water
51
[iii
LIST OF SYMBOLS/ ABBREVIATIONS/ NOTATIONS/ TERMS
A/)
-
Air-to-Iuel ratio
ș
-
HalI angle oI diIIraFted beam
Ȝ
-
:avelength oI the [-rays
ȕ
-
Peak width
L!
-
PartiFle si]e
F
-
CubiF
Ce22
-
Cerium o[ide/ Feria
C2
-
Carbon mono[ide
d
-
Interplaner spaFing in a Frystal
)TIR
-
)ourier-transIorm inIrared
HC
-
HydroFarbon
m
-
MonoFliniF
N2[
-
Nitrogen o[ides
2SC
-
2[ygen storage FapaFity
PD)
-
Power DiIIraFtion )ile
RT
-
Room temperature
t
-
Tetragonal
T1
-
1 Fonversion temperature
TL2
-
Light-oII temperature
T:C
-
Three-way Fatalyst
;RD
-
;-ray diIIraFtion
=r22
-
=irFonium o[ide/ ]irFonia
[iv
LIST OF APPENDICES
APPENDIX
NUMBER
TITLE
PAGE
A
CalFulation oI PartiFle Si]es
64
B
CalFulation oI Gas Conversion in PerFentage
65
C
DiIIraFtograms oI =r.9Ce.122 prepared by using
5 mL oI water FalFined at: a) 4 žC and b) 6 žC
D
66
DiIIraFtograms oI =r.Ce.222 prepared by using
5 mL oI water FalFined at: a) 4 žC and b) 6 žC
67
CHAPTER I
INTRODUCTION
1.1
Air Pollution
Air pollution is the presenFe oI material in air in Tuantities large enough to
produFe harmIul eIIeFts. The undesirable materials may damage, vegetation, human
property, or the global environment as well as Freate aesthetiF insults in the Iorm oI
brown or ha]y air or unpleasant smells >1@.
Air pollution Faused by mobile sourFe had been reFeived muFh attention by
most oI the environmentalist. In the last 6 years the world vehiFles Ileet has
inFreased Irom about 4 million vehiFles to over 7 million, this Iigure is projeFted
to inFrease to 92 million by the year 21 >2@. This will lead to inFrease oI more
and more air pollutant. The engine e[haust Fontains prinFipally three main
pollutants, unburned or partially burned hydroFarbons (HCs), Farbon mono[ide (C2)
and nitrogen o[ides (N2[), mostly N2, in addition to other Fompounds suFh as
water, hydrogen, nitrogen, o[ygen, etF. Sulphur o[ides, though polluting, are
normally not removed by the post Fombustion treatments, sinFe the only eIIeFtive
way is to reduFe them to elemental sulphur, whiFh would aFFumulate in the system
>2@.
2
1.2
Definition and Types of Pollutants
Any solid, liTuid, or gas that is present in the air in a FonFentration that
Fauses some deleterious eIIeFt is Fonsidered an air pollutant. However, there are
several substanFe that, by virtue by their massive rates oI emission and harmIul
eIIeFts, are Fonsidered the most signiIiFant pollutants >3@.
SubstanFes emitted direFtly Irom sourFes are Falled primary pollutants. The
pollutants manuIaFtured in the lower atmosphere by FhemiFal reaFtions among
primary pollutants are Falled seFondary pollutants, they are responsible Ior most oI
the smog, ha]e, and eye irritation and Ior many oI the Iorms oI plant and material
damage attributed to air pollution >4@.
1.3
Effects of Air Pollution
Carbon mono[ide (C2) is a gaseous pollutant whiFh enters the atmosphere
Irom Iour sourFes: Iossil Iuel Fombustion and industrial emissions, biomass burning,
o[idation oI CH4, and o[idation oI non-methane hydroFarbon >5@.
C2 is a Folorless and odorless gas. It is very stable and has a liIetime oI 2 to 4
months in the atmosphere. High FonFentration oI C2 Fan Fause physiologiFal and
pathologiFal Fhanges and ultimately death. C2 is a poisonous inhalent that deprives
the body tissues oI neFessary o[ygen >6@.
N2[ in the atmosphere Fauses environment problems, suFh as photoFhemiFal
o[idant and aFid rain >7@. Nitrogen dio[ide (N22) Fan reaFt with moisture present in
the atmosphere to Iorm nitriF aFid, whiFh Fan Fause Fonsidered Forrosion oI metal
surIaFe. Nitrogen o[ide (N2) is a Folorless gas and its ambient FonFentration is
usually Ior less than .5 ppm. N2 is a preFursor to the Iormation oI nitrogen dio[ide
and is an aFtive Fompound in photoFhemiFal smog Iormation as well >6@.
3
Unburned hydroFarbons in Fombination with the o[ides oI nitrogen in the
presenFe oI sunlight Iorm photoFhemiFal o[idants, Fomponents oI photoFhemiFal
smog, that do have adverse eIIeFts on human health and on plants >6@.
1.4
Catalyst
A Fatalyst is a substanFe that inFreased the rate at whiFh a FhemiFal reaFtion
approaFhes eTuilibrium without itselI beFoming permanently involved in the reaFtion
>@.
BasiFally, Fatalysts are Fonsidered as FhemiFal Fompounds Fapable oI
direFting and aFFelerating thermodynamiFally Ieasible reaFtions while remaining
unaltered at the end oI the reaFtion, whose thermodynamiF eTuilibrium they
FonseTuently Fannot Fhange >9@.
Catalysis is homogeneous when the Fatalyst is soluble in the reaFtion
medium, and heterogeneous when Fatalyst is e[isting in a phase distinFtly diIIerent
Irom the phase oI the reaFtion medium. In most instanFes oI heterogeneous Fatalysis,
the Fatalyst is a solid that is brought into FontaFt with gas or liTuid reaFtants to bring
about a transIormation >9@.
1.5
Catalytic Converter
Nowadays, more than 95 oI vehiFles produFed in the world are eTuipped
with a FatalytiF Fonverter, whiFh Ior the gasoline-Iuelled engines, is almost
e[Flusively based on the so-Falled three-way Fatalyst (T:C). T:Cs are Fapable oI
simultaneously and eIIiFiently Fonverting C2, hydroFarbon (HC) and N2[ into
harmless C22. H22 and N2, provided that the so-Falled and air-to-Iuel ratio (A/)) is
Fonstantly kept at the stoiFhiometry >1@. A typiFal design oI a modern three-way
FatalytiF Fonverter is reported in )ig. 1.1. BasiFally, it is a stainless steel Fontainer
4
whiFh inForporates a honeyFomb monolith made oI Fordierite
(2Mg2.2Al223).5Si22) or metal >2@.
Figure 1.1: Diagram oI a typiFal FatalytiF Fonverter
1.6
Three-way Catalysts
Automobiles under severe driving Fonditions suFh as a long-distanFe
Fontinuous running usually generate high temperature in the FatalytiF Fonverter, that
may Fause thermal sintering oI both metal aFtive phases and Fatalyst support, and
Iinally leads to Fatalyst deaFtivation. 2n the other hand, at Fool start, the Fatalyst
usually shows low FatalytiF aFtivity. ThereIore, a satisIaFtory FatalytiF eIIiFiently at
high temperature and a promoted light-oII reaFtion behavior at Fool start are
demanded Ior the Furrent three-way Fatalysts (T:Cs) >11@.
Three-way Fatalysts (T:Cs) have been widely used to reduFes pollutant
emissions Irom gasoline engine powered vehiFles >12@. 9arious three-way Fatalysts
(T:Cs) are widely used in Far e[hausts Ior the Fonversion oI poisonous gases (C2,
N2[ and hydroFarbons) to harmless H22, C22 and N2. These Fonverters, beFause oI
their eIIeFtiveness, beFome Fompulsory part oI the modern automobile >13@.
5
The FonFept oI using Fatalyst to Fonvert C2, N2[, and HC to less
environment aFtive Fompounds suFh as nitrogen, water and Farbon dio[ide was well
established praFtiFe prior to the need arising on motor vehiFles. The prinFipal
reaFtions are shown in Table 1.1 >14@.
Table 1.1: ReaFtions oFFurring on automobile e[haust Fatalyst
Oxidation Reactions
2C2 22 ĺ 2C22
HC 22 ĺ C22 H22
Reduction Reactions
2C2 2N22 ĺ 2C22 N2
HC N2 ĺ C22 H22 N2
SinFe C2 and HC emission are removed by o[idation whereas N2[ may only
be removed by reaFtion with reduFing agents, the elimination oI all three pollutants
Fan only be aFhieved by separating the o[idation and reduFtion IunFtions in
appropriate reaFtors or by design oI seleFtive Fatalyst on whiFh the two reaFtions
may proFeed simultaneously >15@.
The development oI the three-way Fatalyst (T:C) was diFtated by the need
to simultaneously Fonvert the HC, C2, and N2[, present in the automobile e[haust
to H22, C22 and N2 >16@.
1.7
Zirconium Oxide or Zirconia
=irFonium o[ide or ]irFonia is widespread in nature as a traFe mineral,
baddeleyite. In its pure Iorm, properties suFh as high hardness, low wear resistantFe,
low FoeIIiFient oI IriFtion, high elastiF modulus, FhemiFal inertness, good ioniF
FonduFtivity, low thermal FonduFtivity, and high melting temperature have made
]irFonia a teFhnologiFally important material. These uniTue properties enable a wide
range oI appliFation oI ]irFonia suFh as struFtural materials, thermal barrier Foatings,
6
solid-state eleFtrolytes, solid Iuel Fells, gate dieleFtriFs, o[ygen sensors, and
heterogeneous Fatalysts >17@.
SinFe ]irFonia has a lattiFe with many vaFanFies, it is a good ioniF FonduFtor
at high temperature. These vaFanFies allowed it to be used as an o[ygen sensor to
measure the air-to-Iuel ratio in internal Fombustion engines in order to Fontrol the
emission oI N2[, C2 and hydroFarbon Fompounds >1@.
=r22- based materials have attraFted Fonsiderable interest in reFent deFades.
In a FatalytiF sense, they appear to have some advantages in area oI praFtiFal
appliFation over traditional o[ides, suFh as Si22 and Al223. More signiIiFant is the
IaFt that additives Fan bring about a strong modiIiFation oI the surIaFe struFture oI
]irFonia, in whiFh Fase substitution oI =r4 with dopant Fations results in a rise in
anion vaFanFy FonFentration and FonduFtivity >19@.
The tailored physiFo-FhemiFal properties oI ]irFonia inFluding struFture,
redo[, and aFid-base FharaFteristiFs make it as an attraFtive Fatalyst and Fatalyst
support Ior a number oI reaFtions >2@. In IaFt, due to its aFid-base biIunFtional
properties, it Fatalyses the hydrogenation oI diIIerent substrates suFh as Ior e[ample
ben]oiF aFid, Farbo[yliF aFids, and Farbon mono[ide. However, the main use oI
]irFonia is as an eIIiFient support Ior a variety oI FatalytiF systems >21@.
=irFonia is also widely used in optiFal Iields beFause oI its high reIraFtive
inde[, large optiFal band gap, and low optiFal loss and sFatter in the inIrared region.
It is also useIul Ior making high-reIleFtivity mirrors, laser gyros and broadband
interIerenFe Iilters >22@. Depending on IaFtors suFh as preparation method, pH,
temperature, and kinetiF meFhanism, synthetiF ]irFonia shows three Frystalline
phases: monoFliniF (m), tetragonal (t), and FubiF (F) it has also been shown that a
high-pressure orthorhombiF Iorm e[ists >23@. At room temperature, t- and F-phases
metastable, while m-phase is stable. t- and F-phases are stable at high temperature.
They Fan be partially or Iully stabili]ed at room temperature by addition a small
amount oI o[ides (e.g. Ca2, Mg2 and types oI rare earth o[ides) >24@.
7
The monoFliniF phase is stable up to 14 K where it transIorms to the
tetragonal phase, whiFh is stable up to 157 K while the FubiF phase e[ists up to the
melting point oI 29 K. However, the FubiF phase Fan be stabili]ed by the addition
oI divalent Fations suFh as Ca2, Mg2 or Y3 >2@. Several methods have been
developed to stabili]e the tetragonal phase at low temperature. These inFlude the
addition oI dopants (Y223, Ca2, Mg2, Ce22), or the use oI soIt-Fhemistry methods,
Irom whiFh nanoFrystalline materials Fan be obtained >23@.
It is known that tetragonal ]irFonia as a metastable phase e[ists at well below
its normal transIormation temperature as a result oI the Frystalline si]e eIIeFt, the
presenFe oI impurities, or the presenFe oI strain at the domain boundaries in
polydomain tetragonal partiFles >25@.
Tetragonal- =r22 is used as a Fatalyst and Fatalyst support Ior various gas
phase reaFtions >26@. Several studies have shown that the perFentage oI tetragonal
phase oI =r22 (t-=r22) is FruFial Ior the aFtivity and seleFtivity in Fatalysis >27@.
However, a phase transIormation Irom the tetragonal phase to the less reaFtive
monoFliniF phase oI Frystalline =r22 (m-=r22) during the reaFtion prevents the
Iurther appliFation oI =r22. ThereIore, stabili]ing the tetragonal ]irFonia during
reaFtion beFomes an important topiF in Fatalysis Iields >2@. =r22 stabili]ed by Ce22
and other rare earth is known to inFrease durability and removal eIIiFienFy Ior
automotive emission Fontrol >29@.
1.8
Cerium Oxide or Ceria
Cerium o[ide or Feria (Ce22) has been Fonsidered and largely used in the last
years as one oI the most important promoters oI heterogeneous FatalytiF reaFtions
>3@. Cerium o[ide is one oI the most important Fomponents in high-perIormanFe
three-way Fatalyst (T:C) Ior its ability in enhanFing the removal oI Farbon
mono[ide (C2), nitrogen o[ides (N2[) and hydroFarbons (HC) >31@.
Cerium o[ide has been Fonsidered oI potential interest Ior solid o[ide Iuel
Fells and three-way automobile Fatalysts beFause oI its good o[ygen ion
FonduFtivity. Its ability to aFt as an o[ygen buIIer and thereIore to operate
eIIeFtively under Fonditions oI osFillating o[ygen FonFentration has promoted its use
in automobile FatalytiF appliFations >32@.
However, pure Ce22 alone is known to be poorly thermostable. The loss in
surIaFe area is usually related to the Fhanges in the pore struFture and to Frystalline
growth. It is, thereIore, very important to improve its te[tural stability. Doping with
Fations suFh as Al3, =r4, or Si4 may signiIiFantly improve the stability oI the
surIaFe area oI Feria at high temperature >33@.
Among the lanthanide elements, Ferium is the only one that Iorms stable
Fompounds in a tetravalent o[idation (i.e., Ce4) and the Foordination number oI
surIaFe Ce4 Fan vary between Iour and eight, si[ and eight being the Foordination
number oI bulk Ce4. )urthermore, Cerium ions Fan behaves a large 22 trap: due to
its low redo[ potential and Ferium ion Fan easily pass Irom Ce4 to Ce3 >34@.
Ce22 has a FubiF Iluorite-like struFture in whiFh Ferium Foordinates eight
o[ygen anions at the Forners oI a Fube, while o[ygen is tetrahedrally surrounded by
Iour Ferium Fations. It has been demonstrated that the 2[ygen Storage CapaFity
(2SC) oI Ferium o[ide is improved by suitable doping with diIIerent FationiF speFies
and in partiFular with lanthanum >35@.
AgraIiotis et al >32@ studied deposition oI nanophase doped-Feria systems on
FeramiF honeyFomb Ior automotive FatalytiF appliFations. A remarkable
enhanFement on the FatalytiF aFtivity oI Ferium o[ide has been observed when the
power is oI nanophase dimensions beFause oI the large number oI lattiFe deIeFts suFh
as o[ygen vaFanFies present, whiFh provide a large number oI aFtive sites Ior gassolid Fatalysis. The number oI deIeFts Fan be inFreased by partial substitution
(doping) oI the Ferium atoms in the Ferium o[ide lattiFe with other metal atoms oI
lower o[idation state suFh as Ca or Nd. BeFause oI these properties, doped Ferium
nano-o[ides Fan aFt as Fatalyst themselves, reduFing signiIiFantly the need Ior noble
metals.
9
1.8.1
Role of CeO2 in the TWCs
It is an ambitions task to deIine the role oI the Ce22 in the three-way Fatalysis
sinFe multiple eIIeFts have been attributed to this promoter. Ceria was suggested to
>16@:
1.9
(i)
promote the noble metal dispersion
(ii)
inFrease the thermal stability oI the Al223 support
(iii)
promote the water gas shiIt (:GS) and steam reIorming reaFtions
(iv)
Iavour FatalytiF aFtivity at the interIaFial metal-support sites, etF
(v)
promote C2 removal through o[idation employing a lattiFe o[ygen
(vi)
store and release o[ygen under, respeFtively, lean and riFh Fonditions.
Catalysis by Zirconia-Ceria
Ceria-]irFonia solid solutions Fomprise an interesting system with great
potential Ior appliFations in various teFhnologiFal Iields. Depending on Fomposition,
Feria-]irFonia may be used Ior the manuIaFture oI solid o[ide Iuel Fells, gas sensors,
o[ygen semi-permeable membranes Ior steam eleFtrolysis and hot eleFtrodes Ior
magnetohydrodynamiF systems >36@.
Not long ago, in the middle oI 199s, Ce22-=r22 mi[ed o[ides has been
proFlaimed as one oI the most perspeFtive materials Ior appliFation as a Fomponent
oI so-Falled ³three-way Fatalysts´ (T:C) in automotive pollution Fontrol. These
solids are able to neutrali]e simultaneously C2, hydroFarbons and N2[. High
FatalytiF aFtivity oI suFh system Fombines with enhanFed thermal stability and high
2[ygen Storage CapaFity (2SC). The latter is due to the presenFe oI Ferium ions
able to Fhange easily their o[idation state depending on the environment >37@.
Cerium o[ide (Ce22) is used in automotive emissions Fontrol Fatalysts to
regulate the partial pressure oI o[ygen near the Fatalyst surIaFe. Despite its
widespread use and appliFation, pure Ferium o[ide has poor thermal stability and is
1
known to sinter at 1123 K. In order to inFrease its thermal stability, and ability to
store and release o[ygen during operation, ]irFonium is substituted into the FubiF
struFture oI Feria. The addition oI ]irFonium to the FubiF struFture oI Feria is
reported to inFrease the o[ygen storage FapaFity oI the system while enhanFing the
thermal stability under high temperatures as Fompared to pure Feria >3@.
In the last Iew years, it has been eIIeFtively shown that Ce[=r1-[22 solid
solutions in the Feria riFh regions ([
.5) are the most eIIeFtive redo[ promoters at
low temperature (i.e engine Fold start), and so Fan greatly reduFe emissions oI C2,
N2[, and hydroFarbon when aFtive metal is dispersed on the surIaFe >39@.
=irFonia-riFh Fompositions, Ce1-[=r222-į ( [ .3) Iind appliFations as
FeramiF materials and ioniF FonduFtors whereas Feria-riFh o[ides ( [ ! .3) are
e[ploited above all as FatalytiF materials >36@.
Mello et al >4@ studied the perIormanFe oI Pd / Ce.75=r.2522 Fatalyst Ior the
reduFtion oI N2 with ethanol and Fompare with the Pd-Mo Fatalysts. The Pd /
Ce22-=r22 sample showed higher aFtivity Ior the Fonversion oI N2 and higher
seleFtivity Ior N2 Iormation when Fompared to the Pd-Mo23 / Al223 sample. The
C2 Fhemisorption results showed that the Ce=r mi[ed o[ide Fhemisorbed a higher
amount oI C2 , and this is related to a higher reduFibility FapaFity oI this Fompound
when Fompared to Mo23.
The C2 o[idation on Ce22-=r22 mi[ed o[ides prepared via sol-gel teFhniTue
using urea as a hydrolysis Fatalyst was studied >41@. Highly uniIorm nano-si]e solid
solution partiFles oI Feria-]irFonia were attained under the Fonditions oI this study
(Fa 1 žC). The C2 o[idation aFtivity oI the mi[ed o[ides was Iound to be
dependent on Ce/=r ratio, whiFh relates to the degree oI reduFibility. The FatalytiF
aFtivity Ior C2 o[idation deFreases with a deFrease in Ce/=r ratio. This might be
due to the diIIerent in phase Fompositions oI the mi[ed o[ides. It Fan be postulated
that the FubiF phase, Iluorite struFture, whiFh is mainly Iound in Ce1-[=r[22 (where [
.5) Fould be reduFed easily than the tetragonal phase Iound in Ce1-[=r[22 (where
[ ! .5) >41@.
11
Martorana et al >42@ reported on the struFtural modiIiFations oI two Pt/Feria]irFonia Fatalysts in diIIerent Fonditions oI Ilowing gas mi[tures and oI isothermal
treatment temperature this behavior is Fompared with that oI a metal-Iree Feria]irFonia sample. In a Iirst phase, o[ygen Foming Irom the surIaFe layers oI the Feria]irFonia mi[ed o[ide is Fonsumed and no struFtural variation oI the support is
observed. AIter this induFtion time, bulk reduFtion oI Pt/Feria-]irFonia takes plaFe as
a step-like proFess, while the C22 produFtion Fontinues at a nearly Fonstant rate.
This behavior is totally diIIerent Irom that oI the metal-Iree support in similar
reaFtion Fonditions, that show a gradual bulk reduFtion.
Ko]lov et al >43@ investigated the eIIeFt oI diIIerent synthesis methods on the
redo[ property oI Ce22-=r22-Al223. Related to the important oI the preparation
method is the observation that enhanFed reduFibility aIter redo[ FyFling is only
present in bulk o[ides using Fertain preparation methods. Al223 was able to stabili]e
the partiFle si]e oI the mi[ed o[ide during severe redo[ and thermal treatmant.
1.10
Sol-gel Chemistry
Heterogeneous Fatalysts are oIten prepared by wet Fhemistry method suFh as
preFipitation, FopreFipitation, hydrothermal synthesis or sol-gel proFess. The main
advantages oI these low temperature proFesses are to give solids with large speFiIiF
surIaFe area and high porosity in the meso and maFropore ranges. The solid network
is Iormed, Irom the solution, via the hydrolysis and Fondensation oI moleFular
preFursors in solution >44@.
The sol-gel proFess is a useIul synthesis approaFh Ior the preparation oI
amorphous, as well as struFturally ordered materials. Through sol-gel proFess, it is
possible to Fontrol the properties oI the synthesi]ed samples, suFh as porosity and
surIaFe area to obtain homogeneous matriFes >45@.
12
The sol-gel is also Fonsidered to be the most praFtiFal method Ior the
IabriFation oI porous FeramiF membranes. During the sol-gel proFess, the properties
oI the sol, the surIaFe and pore struFture oI the support, the method oI preparing gel
membrane and its drying and Iiring Fonditions are the key IaFtors inIluenFing the
pore struFture and perIormanFe oI membranes >46@.
The sol-gel proFess Ior preparing o[ide glasses is attraFtive as the preparation
is aFFomplished at room temperature without high-temperature melting or hot
pressing. SinFe the preparation are FonduFted in solutions, the homogeneity attained
in the initial reaFtion mi[ture Fan also be retained. The synthetiF proFedure Ior solgel preparation based on aFid or base Fataly]ed hydrolysis oI alko[y-silane
preFursors in aTueous solution, Iollowed by Fondensation, gelation, aging, drying,
and densiIiFation. The teFhniTue is Fapable oI providing speFialty glasses with
optiFally aFtive organiF or inorganiF materials embedded in the matri[, whiFh oIten
have high optiFal purity and e[Fellent dieleFtriF eIIeFts while possessing
transparenFy over a wide visible range. Thus, glasses prepared by the sol-gel proFess
are attraFtive Fandidates Ior optiFal and eleFtro-optiFal appliFations >47@.
The sol-gel teFhniTue works well Ior the synthesis oI Fomple[ metal o[ides
with high phase purity beFause the polymeri]ing gel traps the various metal ion
Fomponents spatially, permitting preFipitation Irom solution where all the metal ions
oFFupy near-neighbor positions in the gel matri[, upon Iurther proFessing and high
temperature FalFinations, the resultant amorphous mi[ture oI metal o[ides,
hydro[ides, and metal salts deFomposes with M-2-M bond Iormation, while having
to diIIuse only a Iew angstroms to their lattiFe positions in a homogeneous solid
solution. )urthermore, the gel matri[ isolates the individual metal o[ide partiFles,
giving rise to nanostruFtured grains aIter the high temperature FalFinations to Iorm
the Iinished metal o[ide >4@.
There is Fonsidered evidenFe that sols, or Folloidal o[ides, Fan play a FritiFal
role as preFursors to the primary partiFles oI Frystalline or amorphous o[ides >49@.
Sols have played a very FritiFal role in the ability to prepare FatalytiF o[ide
struFtures, suFh as washFoats on monolith struFtures, as the sol struFtures play a
13
FritiFal role as the binder phase between aggregates oI o[ides within suFh struFtures
>49@.
Sol struFtures Fan, however, just as likely be mere speFtators in the
Frystalli]ation proFesses whiFh Iorm the Iinal struFtures within gelled sols. A Fase
Fan be made that the term sol-gel is very misleading, in that although sols may be
Iormed as intermediate struFtures in some Fases, they are Flearly not neFessarily
transIormed into the primary partiFles, or elementary struFtures, within the gelled
o[ide >49@.
Gel synthesis involves polymeri]ing moleFular preFursors into a three
dimensional network and subseTuently Fonverting the wet gel into a [erogel by
removing the solvent >5@.
In the sol-gel route synthesis, a stepwise reaFtion sFheme has been
undertaken to Fontrol the ratio oI hydrolysis to Fondensation rates. In general, the
rate oI hydrolysis is Iast Fompared to that oI Fondensation in strong aFidiF Fondition.
ThereIore, a well-ordered he[agonal arrangement oI mesopores is Iormed at low-pH
in aFidiF Fonditions. Meanwhile, in neutral or basiF Fonditions ranging Irom pH 7 to
pH 9, the rate oI Fondensation is Iaster than that oI hydrolysis, and eventually the
materials prepared by a single-step reaFtion at high pH display gel-like struFture
without mesopores. It is henFe an interesting attempt to synthesi]e ordered
mesoporous materials by two-step sol-gel route at lower aFidiF pH Iollowed by a
higher pH >51@.
As in previous work >52, 53@, modiIied sol-gel method is used to prepare a
]irFonia based Fatalyst in this study. ModiIied sol-gel is a method whiFh varies the
teFhniTue to prepare a sol-gel as well as reaFtion Fondition.
14
1.10.1 The Advantages of Sol-gel Approach Over the Traditional Methods of
Preparation
Sol-gel proFessing provides a new approaFh to the preparation oI supported
metal Fatalysts. A well-deIined pore si]e distribution Fan be obtained using this
approaFh. The potential advantages oI sol-gel proFessing inFlude: purity,
homogeneity, and Fontrolled porosity Fombined with the ability to Iorm large surIaFe
area materials at low temperature >54@.
The advantage oI the sol-gel method oI synthesis is that virtually any metal
o[ide system Fan be e[amined, and no speFial apparatus or eTuipment is reTuired.
Besides, its advantages are the Iormation oI FeramiFs oI high purity and good Fontrol
over miFrostruFture and partiFle morphology in the synthesis, typiFally at room
temperature >4@.
1.10.2 Effects of Variables on the Chemistry of the Sol-gel Synthesis
The important variables whiFh must be Fonsidered in the synthesis oI
supported metals by the sol-gel method inFlude pH, water/metal alFo[ide ratio (R),
gelation temperature, metal loading, addition oI dopants, solvent removal, and
pretreatment Fonditions >55@.
A large number oI studies have been perIormed in an eIIort to understand the
eIIeFt oI water on the properties oI the gel. :hen non-stoiFhiometriF amounts oI
water were added, an analysis oI the reaFtion produFts showed that the e[tent oI
polymeri]ation was largely depends on the number oI moles oI water, whiFh was
added >54@. :hen the H22 / alFo[ide ratio is inFreased, the time reTuired Ior the
Iormation oI the gel is also observed to inFrease. This same result is also obtained
when pH is deFreased >54@. An inFrease in the H22 / alFo[ide ratio Flearly leads to
an inFrease in the pore diameter. The surIaFe area appears to go through a ma[imum
when the H22 / alFo[ide ratio is Flose to that Forresponding to stoiFhiometry >54@.
15
The synthesis oI solid Fatalysts using sol-gel proFessing may be perIormed
under aFid Fondition (pH 1.5-6), basiF Fonditions (pH -11) or neutral Fonditions
(pH 7). DiIIerent Fatalysts Fan used to perIorm the hydrolysis reaFtions >54@. Under
strongly aFidiF Fonditions, hydrolysis oFFurred very rapidly and that gel Iormation
times were inFreased substantially. Hydrolysis is slower and the polymeri]ation is
Fataly]ed by the base. Under these Fonditions, gelation times are Fonsiderably slower
>54@.
The reaFtion pH is very important in determining the Iinal properties oI the
material whiFh is synthesi]ed. Under basiF Fonditions, the partiFles whiFh are
initially Iormed have a diameter oI appro[imately 1 nm. These partiFles inFrease in
si]e during the synthesis. The resultant gel tends to be mesoporous or maFroporous.
:hen the reaFtion is perIormed at a pH oI 7, the partiFles in the sol vary between 2.5
and 2 nm. )or this reason, the resultant gel has a non-uniIorm pore si]e
distribution. Under aFid Fonditions the partiFles in both the sol and the gel are very
uniIorm. They vary in si]e between .5 and 3. nm and in general have very high
porosities. It is also important to note that the pore volume Forresponding to meso
(2-5 nm) and maFro (!5 nm) pores inFrease at the e[pense oI miFropores (2.
nm) with inFreasing pH >54@.
In the sol-gel proFess, drying is regarded as an important proFedure in the
determination oI the perIormanFe oI resultant [erogels >56@. Among the many
drying teFhniTue, thermal drying is employed most IreTuently Ior FonvenienFe, and a
preFeding ambient drying is usually perIormed. It is assumed that shortening the
ambient drying period, along with shortening the total drying proFedures, Fan tailor
the FharaFteristiFs oI the resultant [erogels >56@.
In some Fases, the gel is aged beIore drying. Aging Fan take the Iorm oI a
³redispersion treatment´ whiFh allows dissolution and preFipitation oI material Ior a
degree oI ³Iine tuning´ oI the network¶s struFture. The solvent is subseTuently
removed by either (i) evaporative drying or (ii) a superFritiFal drying step.
SuperFritiFal drying has the advantage oI eliminating the liTuid/vapor interIaFe
during drying that Fould otherwise lead to partial Follapse oI the network struFture-
16
most notably loss oI surIaFe area and pore volume-due to high diIIerential Fapillary
pore pressures >57@.
1.10.3 Preparation of Catalysts by Sol-gel Method
The preparation oI supported metal Fatalysts by sol-gel method is uniTue
beFause the metal preFursor is mi[ed homogeneously together with the moleFular
preFursor oI the support, resulting in a greater degree oI Fontrol over the Iinal
properties oI the Fatalyst >55@.
There are two types oI sol-gel method depending on the FhemiFal nature oI
the preFursors suFh as inorganiF based sol-gel method and organiF based sol-gel
method. InorganiF based sol-gel method involved inorganiF salt whiFh easily
dissolved in water whereas organiF based sol-gel method involved organometalliF
salts/ Fomple[es suFh as alko[ides whiFh Fan be dissolved in organiF solvent.
Sol-gel proFessing in whiFh metalorganiF preFursors are mi[ed with metal
preFursors to Iorm a homogeneous solution. The metalorganiF is hydroly]ed through
the addition oI water FareIully Fontrolling the pH and the reaFtion temperature. As
hydrolysis and polymeri]ation oFFur, Folloidal partiFles or miFelles with an
appro[imate diameter oI 1 nm are Iormed. These partiFles Fontinue to inFrease in
si]e until a metal o[ide gel (alFogel) is Iormed. The solvent Fan be eliminated by
heat treatment in air to Iorm a [erogel. The metal o[ide gel (hydrogel) is Iormed by
using inorganiF salt as a preFursor. The solvent Fan be dried to Iorm a [erogel >54@.
Most ]irFonia Fompounds Fan be used as preFursors oI ]irFonium o[ide in the
sol-gel proFess. These preFursors oI ]irFonia Fan be FlassiIied as ]irFonium
alko[ides (]irFonium propo[ide, ]irFonium tetra-n-buto[ide etF.) and inorganiF
]irFonium salts (]irFonium o[yFhloride, ]irFonium aFetate etF.) >46@.
17
:hen ]irFonia is prepared using the sol-gel method, the tetragonal phase Fan
be stabili]ed at low temperature, depending on pH and the type oI Fatalyst used in
the synthesis. The 2H groups retained in the bulk in this method Iavour stabili]ation
oI the tetragonal phase, whereas when positive ions are present (e.g., H, Li, Na)
the monoFliniF phase is produFed at low temperature >23@.
The Frystalline properties oI ]irFonia synthesi]ed by the preFipitation and solgel methods were Fomparatively studied >1@. Both synthesis methods gave rise to
nanoFrystalline ]irFonia. The samples FalFined at žC and prepared by the
preFipitation had average Frystalline si]es less than 1 nm, whiFh were two times
smaller than the Forresponding value obtained in the sol-gel samples. Both
tetragonal and monoFliniF nanoFrystalline phases had atomiF deIeFts in
FonFentrations that depended on the synthesis method and annealing temperature.
Rossignol et al >5@ studied the preparation oI ]irFonia-Feria solid solutions
(=r1-[Ce[22) with ” [ ”1) by two diIIerent methods: Fonventional ³FopreFipitation´
and ³modiIied sol-gel´ preparation. Both the struFture and the te[ture oI those solids
depend on the synthesis and the ]irFonium preFursor. )or solids prepared by the
modiIied sol-gel method, with a surIaFe area oI 6 m2g-1, a new FubiF phase
(=r.25Ce.7522) is obtained, while an orthorhombiF ]irFonia phase was identiIied Ior
solids prepared either by FopreFipitation or sol-gel methods. The sol-gel method was
partiFularly eIIiFient Ior preparation oI Ce-=r-2 mi[ed o[ides with high Ferium
Fontents.
Lope] et al >59@ investigated the improvement oI struFtural and
morphologiFal properties oI Mn-=r mi[ed o[ides by sol-gel method with varing
Mn/=r ratio in the entire Fompositional range. This proFedure allows an e[Fellent
Fontrol over relevant properties oI the synthesi]ed materials, namely Fompositional
homogeneity, purity, and porous struFture.
Aguilar et al >23@ reported a systematiF analysis oI the Frystalli]ation proFess
oI amorphous sol-gel samples and the thermal behavior oI ]irFonia Fogelled with
siliFa, in the Fomplete =r22-Si22 system range, annealing the samples with long
thermal treatments at temperature between 1 žC-14 žC. =r22-Si22 mi[ed o[ides
1
prepared using the sol-gel teFhniTue are promising Fatalysts, or Fatalyst supports, in
petroFhemiFal proFesses. )or e[ample, it has been shown to be useIul in the nhe[ane isomeri]ation reaFtion to high oFtane, employing biIunFtional ]irFonia-siliFa
Fatalysts in produFts suFh as 2,2-dimethylbutane and 2,3-dimethylbutane.
)arias et al >45@ investigated on the sol-gel synthesis oI alumina and 1:1
mi[ed o[ides oI Al223-=r22, Si22-Ti22, =r22-Ti22 and Al223-Ti22. Due to their
speFies with aFidiF sites oI diIIerent types (mainly Br|nsted sites Ior Si22 and Lewis
sites Ior the other o[ides) and strengths, the mi[ed o[ides are interesting matriFes
Irom a FatalytiF point oI view.
1.11
Statement of the Problem and the Needs of the Study
The automobile e[haust is identiIied as one oI the major sourFes oI air
pollution >29@. Due to inFomplete Fombustion oI Iuel, automobiles emits to[iF gases
suFh as Farbon mono[ide (C2), hydroFarbon (HC), and nitrogen o[ides (N2[) to the
environment. The way to reduFe these to[iF gases released to the air is by Fonverting
them simultaneously to non-to[iF gases and to do this, a three-way Fatalyst is
developed. Tetragonal =r22 is used as Fatalyst and Fatalyst support Ior various gas
phase reaFtion >26@. Several studies have shown that the perFentage oI tetragonal
phase oI =r22 is FruFial Ior the aFtivity and seleFtivity >27@.
SinFe the tetragonal phase oI =r22 Fan serve a good FatalytiF site, thereIore
this researFh will be Farried out to study the optimum Fondition on the highest
Iormation oI single phase tetragonal =r22. This researFh will be FonFentrated on the
preparation oI the three-way Fatalyst based on ]irFonium o[ide using modiIied solgel method.
19
1.12
Research Objectives
The objeFtives oI this researFh are:
1. To prepare a single-phase tetragonal ]irFonium o[ide doped with
Ferium o[ide Fatalyst by modiIied sol-gel method.
2. To eluFidate the physiFal FharaFteristiFs oI Fatalyst using various
analytiFal methods Ior Iurther understanding oI the properties oI the
Fatalyst Fonsisting oI single-phase tetragonal ]irFonia.
3. To evaluate the perIormanFe oI the Fatalyst obtained towards C2
Fonversion/ o[idation.
1.13
Scope of Research
This researFh is Farried out to study the optimum Fonditions on the highest
Iormation oI single phase tetragonal =r22. Three parameters will be studied in this
study to prepare a single phase tetragonal ]irFonia doped with Feria Fatalyst, vi]
amount oI water, amount oI dopants and FalFination temperatures. In this study, the
preFursors will be dissolved in a minimum amount oI water to prepare a Fatalyst. A
series oI =r[Ce1-[22 Fatalysts will be prepared by varying the atomiF perFentage
ratios, over the Fomposition range Irom 5-5 oI Ferium loading. The FalFination
temperature start at 4 ÛC will be Fhosen based on previous studies on Fatalyst
based on metal o[ides, whiFh reported that the Fatalysts were mostly aFtive at this
temperature >6@.
The physiFal properties oI Fatalysts will be FharaFteri]ed with ;-Ray
DiIIraFtion (;RD), surIaFe area analysis, and )ourier-TransIorm InIrared
SpeFtrosFopy ()TIR). The best atomiF perFentage ratio oI Fatalyst Ior the highest
Iormation oI single phase tetragonal =r22 will be seleFted Ior Iurther study on the
FatalytiF aFtivity towards C2 Fonversion.
CHAPTER II
EXPERIMENTAL
2.1
Chemicals
=irFonium o[yFhloride and Ferium (III) nitrate he[ahydrate were used as the
preFursors in this study. =r2Cl2.H22 was purFhased Irom E. MerFk, Darmstadt
whereas Ferium (III) nitrate he[ahydrate, Ce(N23)3.6H22, was purFhased Irom E,
MerFk. D-61 Darmstadt, ).R. Germany.
2.2
Experiment
This researFh is divided into 3 steps:
i)
Preparation oI the Fatalyst using modiIied sol-gel method,
ii)
CharaFteri]ation oI the Fatalyst,
iii)
SeleFted Fatalyst samples were tested Ior Farbon mono[ide Fonversion
(C2).
21
2.3
Preparation of Zirconia Based Catalysts Doped with Ceria by Modified
Sol-Gel Method
=irFonia based Fatalysts doped with Feria were prepared via modiIied sol-gel
method ()igure 2.1). Catalyst samples with general Iormula =r[Ce1-[22 were
prepared aFFording to their atomiF perFentage ratios (=r.95 : Ce.5). Catalyst sample
was prepared by varying the amount oI water. A ]irFonium o[yFhloride solution was
prepared by dissolving the salt (5 g) in distilled water ( mL) in a round-bottom Ilask
(5 mL) and stirred Fontinuously. To this solution, a Ferium (III) nitrate he[ahydrate
solution was then added slowly and stirred Ior 15 minutes. This Ferium (III) nitrate
he[ahydrate solution was prepared by dissolving the salt oI .5 in atomiF
perFentage ratio in 1ml oI distilled water. By using a similar preparation method, the
same atomiF perFentage ratios oI sample were prepared by using a minimum oI water
(5 mL). These proFedures were repeated Ior series oI =rCe22 Fatalysts by varying
the atomiF perFentage ratio as (=r.9 : Ce.1), (=r. : Ce.2), (=r.7 : Ce.3), and
(=r.5 : Ce.5). The resultant transparent solution was then poured into an
evaporating dish and allowed to dry in an oven at 7 žC Ior 2 days until Fompletely
dried.
Retort
stand
Round-bottom
Ilask
MagnetiF
stirrer
=r22 based
Fatalyst doped
with Ce22
MagnetiF spinner
)igure 2.1
SFhematiF diagram oI the Fatalyst preparation set-up using modiIied
sol-gel method
22
2.4
Drying and Calcination
Drying is desFribed as the elimination oI water or solvent Irom the pores oI a
solid. Drying Fan be done in a Fonventional drying oven at temperature oI
1-2 žC. It is aFFompanied by physiFo-FhemiFal and physiFo-meFhaniFal
transIormation that Fan proIoundly modiIy the struFture oI the gel >61@. All prepared
samples were dried in the oven at temperature oI 7 žC Ior two days until Fompletely
dried. AIter drying, dried samples were then grinded with pestle and mortar beIore
FalFined in the IurnaFe at 4 žC and 6 žC Ior 17 hours with ramping time oI two
hours. These temperatures were Fhosen based on previous studies on Fatalyst based
on metal o[ides, whiFh reported that the Fatalysts were mostly aFtive at these two
temperatures >6@.
The type oI FalFination is assumed to be FalFination in air, typiFally at a
temperature higher than the antiFipated temperatures oI the Fatalysts reaFtion and
Fatalyst regeneration >61@. CalFination has several purposes. 2ne is to eliminate
e[traneous material suFh as binders, as well as volatile and unstable anions and
Fations that have been previously introduFed, but are not desired in the Iinal Fatalyst.
SeFond, a substantially elevated temperature is usually needed to inFrease the
strength oI the Iinal pellet or e[trudate by Fausing inFipient sintering. E[Fessive
sintering will reduFe the Fatalyst aFtivity by reduFing surIaFe area, and it may also
Fause diIIusion imitations by reduFtions oI pore si]e, so an optimum is desired >62@.
II a metalliF Fatalyst is the ultimate goal, Fonversion to the o[ide Iorm is
IreTuently sought prior to reduFtion. II a Fomple[ Fatalyst is the goal, a substantially
elevated Iiring temperature may be reTuired to Fause mi[ing by diIIusion oI
individual speFies to Iorm a desired Fompound or Frystal phase. In any event, the
Fatalyst should be heated under Fontrolled Fonditions to a temperature at least as high
as will be enFountered in the plant reaFtor to remove bound water, Farbon mono[ide,
etF. II these deFompositions oFFur to a signiIiFant e[tent in the plant, they may Fause
struFtural weaknesses in pellets, leading to the breakup, dusting, and so on, that may
Fause e[Fessive pressure drop and premature reaFtor shutdown >62@.
23
2.5
Characterization Techniques
2.5.1
X-Ray Diffraction (XRD)
Catalyst samples were grinded into Iine powders by using pestle and mortar.
EaFh sample was then evenly distributed on the surIaFe oI the sample holder by
using a pieFe oI glass slide and plaFed onto a Siemens D5 ;-ray diIIraFtometer
eTuipped with Cu-KĮ (Ȝ
1.54 c) radiation. Data were FolleFted over the range oI
2ș Irom 1 ž up to ž by using a step sFan oI .5 ž and a step time oI 1 seFond per
step. Peaks position, width and intensity were then identiIied by Fomparison done
with an aFFumulated Powder DiIIraFtion )iles (PD)), whiFh Fomes together with the
soItware.
;-ray DiIIraFtion (;RD) is a powerIul teFhniTue used to uniTuely identiIy
the Frystalline phases present in material and to measure the struFtural properties
(strain state, grain si]e, phase Fomposition, preIerred orientation, and deIeFt
struFture) oI these phases >63@. )igure 2.2 shows the basiFs Ieatures oI an ;RD
e[periment, where the diIIraFtion angles 2ș is the angle between the inFident and
diIIraFted ;-rays. In a typiFal e[periment, the diIIraFted intensity is measured as a
IunFtion oI 2ș and the orientation oI the speFimen, whiFh yields the diIIraFtion
pattern.
;-ray diIIraFtion is the elastiF sFattering oI ;-ray photons by atoms in a
periodiF lattiFe. The sFattered monoFhromatiF ;-rays that are in phase give
FonstruFtive interIerenFe. DiIIraFtions oI ;-rays by Frystal planes allow one to
derive lattiFe spaFing by using the Bragg relation (eTuations 2.1) >64@:
nȜ
where
2d sin ș
n
1, 2, 3
(2.1)
Ȝ
wavelength oI the ;-rays
d
distanFe between two lattiFe planes
ș
angle between the inFoming ;-rays and the normal to the
reIleFting lattiFe plane
n
integer Falled order oI the reIleFtion
24
II one measures the angles, 2ș under whiFh FonstruFtively interIering [-rays
leave the Frystal, the Bragg relation (eTuation 2.1) gives the Forresponding lattiFe
spaFing, whiFh are FharaFteristiF Ior a Fertain Fompound >64@.
)igure 2.2
BasiF Ieatures oI a typiFal ;RD e[periment
;-rays diIIraFtion has an important limitation: Flear diIIraFtion peaks are only
observed when the sample possesses suIIiFient long-range order. The advantage oI
this limitation is that the width (or rather the shape) oI diIIraFtion peaks Farries
inIormation on the dimensions oI the reIleFting planes. DiIIraFtion lines Irom perIeFt
Frystals are very narrow. )or Frystalli]e si]e below 1 nm, however, line
broadening oFFurs due to inFomplete destruFtion interIerenFe in sFattering direFtions
where the [-rays are out oI phase. The Iull width at halI height ():HM) oI the
diIIraFtion lines also give an appro[imate measurement oI the partiFle si]e oI the
Fatalyst by using SFherrer eTuation in getting the aFtual value oI the partiFle si]e.
25
The SFherrer Iormula relates Frystal si]e to line width:
L!
kO
E FosT
(2.2)
in whiFh
L!
measure Ior the dimension oI the partiFles in the direFtion
perpendiFular to the reIleFting plane
Ȝ
;-rays wavelength
ȕ
peak width
ș
angle between the beam and the normal on the reIleFting plane
K
Fonstant (oIten taken as 1)
;-rays diIIraFtion is the main teFhniTue Ior the investigation oI bulk
struFture, to monitor the kinetiFs oI bulk transIormations and to estimate partiFle
si]es. In Fatalyst studies, ;RD Fan provide inIormation oI the possibilities Ior the
presenFe oI amorphous phases and also identiIiFation oI Frystalline phases in the
Fatalyst. )or FrystallographiF phases, ;RD gives a sharp and narrow diIIraFtion
lines whereas Ior the amorphous phases, it gives either very broad and weak
diIIraFtion lines or no diIIraFtion at all. >65@.
2.5.2
Surface Area Analysis
SurIaFe area analysis was Farried out to determine Fatalyst surIaFe area. The
Pulse Chemisorb 275 instrument was used Ior surIaFe area analysis. The Iinely
grinded sample was weighed at .5 g and then poured into a dry and Flean sample
tube. The sample was out-gassed at 3 žC Ior 2 hours, then the sample was leIt to
Fool to room temperature beIore measurement is Farried out. The absorptiondesorption measurement was Farried out manually aIter the Falibration oI the
instrument is done.
26
SurIaFe area measurements were aFFomplished using a 3 N2 / 7 He gas
mi[tures. LiTuid nitrogen is the FryogeniF liTuid in most instanFes. 2nly nitrogen
gas is physiFally adsorbed at liTuid nitrogen temperature, the helium serving as an
inert Farrier.
Nitrogen with the volume oI 1. Fm3 at 22 žC and 76 mmHg represents a
single layer iI nitrogen moleFules physiFally adsorbed on a surIaFe oI 2.4 m2. Thus
when the instrument is adjusted to indiFate 2.4 m2 oI sample surIaFe Ior every
1. Fm3 oI gas adsorbed, it displays direFtly the total sample surIaFe area. Small
ambient temperature deviations Irom 22 žC are relatively insigniIiFant, but a value
diIIering Fonsiderably Irom 2.4 may be more appropriate in some loFations Iar
removes Irom sea level elevation.
2.5.3
Fourier–Transform Infrared Spectroscopy (FTIR)
Catalyst samples were prepared Ior speFtrosFopy analysis using the potassium
bromide, KBr, pellet teFhniTue. 1 ± 3 mg oI the Iinely grinded sample was well
mi[ed with 3 mg oI KBr powder (1: 1) and then the mi[ture was pressed Ior 5
minutes in evaFuable die under 1 tonne oI pressure to give a transparent disF. The
)TIR speFtrum were reForded in the speFtral region Irom 4 to 4 Fm-1 at the
resolution oI 4 Fm-1 and 1 sFans to ensure better signal-to-noise ratio by using
Shimad]u 3 )ourier TransIorm InIrared SpeFtrometer.
The most Fommon appliFation inIrared speFtrosFopy in Fatalysis is to identiIy
adsorbed speFies and to study the way in whiFh these speFies are Fhemisorbed on the
surIaFe oI the Fatalyst. In addition, the teFhniTue is useIul in identiIying phases that
are present in preFursor stages oI the Fatalyst during its preparation. Sometimes the
inIrared speFtra oI adsorbed probe moleFules suFh as C2 and N2 give valuables
inIormation on the adsorption sites that are present on the Fatalyst >64@.
27
InIrared speFtrosFopy is the most Fommon Iorm oI vibrational speFtrosFopy.
9ibration is divided into basiF Fategories oI stretFhing and bending. InIrared
radiation Ialls into three Fategories, as indiFated in Table 2.1. It is the mid inIrared
region that is oI our interest.
Table 2.1
Region
Classification of Infrared Radiation
:avelength
Energy
:avenumber
(ȝm)
(me9)
(Fm-1)
InIrared
1 - 1
1.2 - 124
1 - 1
)ar
1 - 5
1.2 - 25
1 - 2
LattiFe 9ibrations
Mid
5 - 2.5
25 - 496
2 - 4
MoleFular 9ibration
Near
2.5 - 1
496 - 124
4 - 1
2vertones
a) 1 me9
.655 Fm-1
DeteFtion oI
The )TIR teFhniTue is used to obtain inIormation about IunFtional group in a
Fompound. DiIIerent IunFtional group or diIIerent moleFules give diIIerent vibration
IreTuenFies. In order to absorb inIrared radiation, a moleFule must undergo a net
Fhange in dipole moment as a FonseTuenFe oI its vibrational motion. The dipole
moment is determined by the magnitude oI the Fharge diIIerenFe and the distanFe
between the two Fenters oI Fharge. II the IreTuenFies oI the radiation matFh a natural
vibrational IreTuenFy oI the moleFules, a net transIer oI energy oFFurs that results in
a Fhange in the amplitude oI the moleFular vibration, and absorption oI the radiation
is the FonseTuenFe >64@.
2
2.6
Catalytic Activity Testing Measurement
CatalytiF aFtivity testing Ior seleFted samples were Farried out by using a
Ii[ed bed Fustom made miFroreaFtor. .5 g Iinely grinded samples were weighed
and paFked into a pyre[ sample tube. The sample was plaFed against the glass sinter
on the side oI the inFoming stream. Dried siliFa powder was paFked in on either side
and held in plaFe with glass wool ()igure 2.3). The siliFa aFted as an insulator in
order to stabili]e the temperature around the sample, as a FonduFtor medium Ior heat
and its inert property does not interIere with the FatalytiF reaFtion in the IurnaFe.
Pyre[ sample tubes were then loaded into the IurnaFe bloFk and the samples were
preheated at 32 žC to 33 žC Ior an hour in a stream oI air (21 22 79 N2) at
the Ilow rate oI 9 mL/min beIore being e[posed to the desired gas mi[ture. This is to
aFtivate the Fatalyst in order to prepare the Fatalyst in the desired state beIore testing.
Catalyst samples were then Fooled at room temperature and tested by passing Farbon
mono[ide (C2) to determine the Fonversion oI Farbon mono[ide (C2) to Farbon
dio[ide (C22). Catalysts were tested using a mi[ture oI C2 4 (4 C2, 2.16 22
and 75.4 N2) in riFh o[ygen Fondition. The peak Ior the C2 gas was deteFted by
the )TIR speFtrometer in the regions Irom 26 to 223 Fm-1 whereas C22 was
deteFted at 2259 to 2379 Fm-1.
The aFtivity oI the Fatalyst samples was reForded as a IunFtion oI the
Fonversion oI reaFtant gas with respeFt to the temperature. The data were reForded
in term oI peak area. The aFtivity oI the Fatalyst was measured until 4 žC or until
no more Fhanges oI Fonversion Fan be deteFted.
29
Glass :ool
Dry SiliFa Powder
.5 g Catalyst
Gas
Mi[ture
Gas
Mi[ture
Dry SiliFa
Powder
Glass Sinter Glass :ool
Sample Tube
Gas )low
)igure 2.3
SFhematiF diagram oI the miFroreaFtor sample tube
CHAPTER III
RESULTS AND DISCUSSIONS
3.1
Influence of Variables on the Formation of Tetragonal Phase ZrO2
Three variables were studied on the preparation oI ]irFonia-based Fatalyst
doped with Feria by using modiIied sol-gel method, vi] amount oI water, amount oI
dopants and FalFination temperatures. These variables were investigated to
determine the optimum preparation Fondition Ior the Iormation oI tetragonal phase
]irFonia. All the Fatalyst samples were FharaFteri]ed via ;-Ray DiIIraFtion (;RD)
to obtain the inIormation oI the bulk struFture, Frystalline phases and to estimate
partiFle si]es. In Fatalyst studies, ;-Ray Powder DiIIraFtion (;RPD) is used to
investigate the Frystalline phase transIormation oI the mi[ed o[ides Fatalysts system
with respeFt to the FalFination temperature. The inIormation oI Frystalline phases
was identiIied using tabulations oI reIerenFe patterns by Fomparing the 2ș values oI
the samples with those oI phases Irom the powder diIIraFtion Iile (PD)) >66@.
PartiFle si]es Ior the samples were FalFulated by using the SFherrer Iormula as shown
in Appendi[ A. SeleFted samples were then FharaFteri]ed via surIaFe area analysis
to obtain the inIormation oI surIaFe area. Besides, )ourier TransIorm InIrared
SpeFtrosFopy ()TIR) analysis was also Farried out to identiIy the presenFe oI speFies
on the surIaFe oI the Fatalyst material.
31
3.1.1
Effect of Amount of Water on the Formation of Tetragonal Phase ZrO2Based Catalyst Doped with CeO2 (Zr0.95:Ce0.05)
The diIIraFtograms pattern obtained Irom the ;RD analysis oI =r.95Ce.522
sample by using diIIerent amount oI water are depiFted in )igure 3.1(a)±(b) while the
peaks assigned are tabulated in Table 3.1.
)or the =r.95Ce.522 sample that was prepared by using mL oI water, the
diIIraFtogram is depiFted in )igure 3.1 (a). Two major phases oI =r22 were
identiIied as tetragonal at 2ș values oI appro[imately 3.245, 5.365, 6.56 and
35.21ž or d-spaFing values oI 2.95, 1.1, 1.54 and 2.55 c (PD) >66@ d-spaFing
values (c) : 2.95, 1.1, 1.54 and 2.54) and monoFliniF phase at 2ș values oI
appro[imately 2.335 and 31.426 ž or d-spaFing values oI 3.15 and 2.4 c (PD) >66@
d-spaFing values (c) : 3.16 and 2.4) were observed. There were no Ferium o[ide
(Ce22) peaks deteFted due to the relatively small loading oI Feria used in the system.
Similar results were obtained Ior the sample by using 5 mL oI water as shown
in )igure 3.1 (b) with the present oI tetragonal phase oI =r22 at 2ș values oI
appro[imately 3.175, 5.211, 6.9, 35.123 and 59.45 žd-spaFing values oI 2.96,
1.2, 1.54, 2.55 and 1.55 c (PD) >66@ d-spaFing values (c): 3.16 and 2.4) were
observed. The Iormation oI monoFliniF struFture phase is also present in the material
with 2ș values oI appro[imately 2.2 and 31.474 ž or d-spaFing values oI 3.15 and
2.4 c (PD) >66@ d-spaFing values (c): 3.16 and 2.4). Again, there were no Ferium
o[ide peaks deteFted due to the relatively small loading oI Feria in the system.
The ;RD patterns Ior sample =r.95Ce.522 prepared by using diIIerent
amount oI water (5 mL and mL) are Fomparatively shown in )igure 3.1 (a)±(b).
The three highest peaks in both diIIraFtograms were due to the e[istenFe oI the
tetragonal phase =r22. 2bviously, the ;RD pattern Ior both samples prepared in
5 mL and mL oI water showed the same trend. This indiFated that the amount oI
water did not aIIeFt the evolution in the phase transIormation oI =r.95Ce.522
Fatalyst. However, Irom the FalFulation oI partiFle si]es Ior both samples by using
SFherrer Iormula as shown in Appendi[ A, it showed that the partiFle si]es Ior the
32
samples in mL oI water were slightly larger than the sample prepared in 5 mL oI
water. The partiFle si]e Ior sample =r.95Ce.522 prepared in mL oI water is
19.75 nm while in 5 mL oI water is 1.9 nm. The data are shown in Table 3.4.
This diIIerent in partiFle si]e may be due to the agglomeration oI the partiFles when
the amount oI water inFreased.
The results above showed that amount oI water did not aIIeFt the Iormation oI
tetragonal phase =r22 in =r.95Ce.522. ThereIore, a Iurther study on the eIIeFt oI
various loading oI Ce22 on the Iormation oI tetragonal phase =r22 was then Farried
out.
Intensity
(a) mL
(b) 5 mL
1
2
3
4
5
6
7
2ș (ž)
=r22 (t)
)igure 3.1
=r22 (m)
DiIIraFtograms oI =r.95Ce.522 using diIIerent amount oI water:
(a) mL and (b) 5 mL
33
Table 3.1
;RD peaks assignment Ior =r.95Ce.522 Fatalyst sample in diIIerent
amount oI water
Amount oI
2ș Angle
d
ReIerenFe
Peaks
:ater (mL)
(ž)
(c)
(d/ c)
Assignment
2.335
3.15
3.16
=r22 (m)
3.245
2.95
2.95
=r22 (t)
31.426
2.4
2.4
=r22 (m)
35.21
2.55
2.54
=r22 (t)
5.365
1.1
1.1
=r22 (t)
6.56
1.54
1.54
=r22 (t)
2.2
3.15
3.16
=r22 (m)
3.175
2.96
2.95
=r22 (t)
31.474
2.4
2.4
=r22 (m)
35.123
2.55
2.54
=r22 (t)
5.211
1.2
1.1
=r22 (t)
59.45
1.55
1.55
=r22 (t)
6.9
1.54
1.54
=r22 (t)
(a) mL
(b) 5 mL
*
m
monoFliniF phase
t
tetragonal phase
34
3.1.2
Effect of Loading of CeO2 on the Formation of Tetragonal Phase ZrO2
The ;RD pattern oI Fatalyst samples varying their atomiF perFentage ratios
are Fomparatively shown in )igure 3.2 and )igure 3.3 whereas the peaks assigned are
tabulated in Table 3.2 and Table 3.3 respeFtively.
The diIIraFtograms oI ]irFonia-based Fatalyst doped with diIIerent amount oI
Feria in mL oI water are depiFted in )igure 3.2 (a)±(d) and the peaks assigned are
tabulated in Table 3.2. DiIIraFtogram oI =r.95Ce.522 Fatalyst as shown in
)igure 3.2 (a) resulted in the Iormation oI tetragonal phase =r22 phase at 2ș values
oI appro[imately 3.245, 5.365, 6.56, and 35.21 ž or d-spaFing values oI 2.95,
1.1, 1.54 and 2.55 c (PD) >66@ d-spaFing values (c): 2.95, 1.1, 1.54 and 2.54).
The =r.95Ce.522 Fatalyst also showed the e[istenFe oI =r22 monoFliniF phase at 2ș
values oI appro[imately 2.335 and 31.426 ž or d-spaFing values oI 3.15 and 2.4 c
(PD) >66@ d-spaFing values (c): 3.16 and 2.4). There were no Ferium o[ide peaks
deteFted due to relatively small loading oI Ferium used in the system.
Similar results were obtained Ior the =r.9Ce.122, =r.Ce.222 and
=r.7Ce.322Fatalyst sample, as shown in )igure 3.2 (b)-(d), with the present oI
tetragonal phase oI =r22 as the main phase and monoFliniF phase oI =r22 were
observed. The peaks assigned are tabulated in Table 3.2. )rom the diIIraFtogram oI
=r.Ce.222 Fatalyst, it indiFated that the monoFliniF oI =r22 phase has slightly
deFreased in intensity as the amount oI Feria in the mi[ed o[ides inFreased.
AFFording to the ;RD patterns oI the =r.7Ce.322 sample shown in )igure 3.2 (d),
the monoFliniF phase oI =r22 had obviously reduFes in intensity. The peaks whiFh
were still assigned to tetragonal =r22 were observed as the main phase.
)rom the ;RD patterns, it is shown that the monoFliniF phase oI =r22 has
deFreased in intensity as the Ferium loading inFreased, over the Fomposition range
Irom 5 to 3 Ferium, while the tetragonal phase oI =r22 remained as the
dominant phase.
35
(a) =r.95Ce.522
Intensity (b) =r.9Ce.122
(F) =r.Ce.222
(d) =r.7Ce.322
1
2
3
4
5
6
7
2ș (ž)
=r22 (t)
)igure 3.2
=r22 (m)
DiIIraFtograms oI =r[Ce1-[22 Fatalyst with diIIerent amount oI Feria
in mL oI water (a) =r.95Ce.522, (b) =r.9Ce.122,
(F) =r.Ce.222, and (d) =r.7Ce.322
36
Table 3.2
;RD peaks assignment Ior =r[Ce1-[22 Fatalyst in mL oI water
Sample
2ș Angle
=r.95Ce.522
=r.9Ce.122
=r.Ce.222
=r.7Ce.322
*
m
d (c)
ReIerenFe
Peak
d (c)
Assignment
2.335
3.15
3.16
=r22 (m)
3.245
2.95
2.95
=r22 (t)
31.426
2.4
2.4
=r22 (m)
35.21
2.55
2.54
=r22 (t)
5.365
1.1
1.1
=r22 (t)
6.56
1.54
1.54
=r22 (t)
2.316
3.15
3.16
=r22 (m)
3.126
2.96
2.95
=r22 (t)
31.447
2.4
2.4
=r22 (m)
35.67
2.56
2.54
=r22 (t)
5.195
1.2
1.1
=r22 (t)
59.4
1.54
1.54
=r22 (t)
2.33
3.15
3.16
=r22 (m)
29.93
2.9
2.95
=r22 (t)
31.371
2.5
2.4
=r22 (m)
34.651
2.59
2.54
=r22 (t)
49.919
1.3
1.1
=r22 (t)
59.354
1.56
1.54
=r22 (t)
29.2
2.99
2.95
=r22 (t)
34.562
2.59
2.54
=r22 (t)
49.515
1.4
1.1
=r22 (t)
49.9
1.3
1.
=r22 (t)
59.146
1.56
1.54
=r22 (t)
monoFliniF phase
t
tetragonal phase
37
The diIIraFtograms oI ]irFonia-based Fatalysts doped with diIIerent loading
oI Feria in 5 mL oI water are depiFted in )igure 3.3 (a)-(e) and the peaks assigned are
tabulated in Table 3.3. Peaks attributed to the tetragonal =r22 phase and the
Iormations oI the monoFliniF =r22 phase were observed Irom the )igure 3.3 (a)-(b).
)or the =r.Ce.222 Fatalyst, the monoFliniF phase oI =r22 had slightly
deFreased with respeFt to the inFreasing amount oI Feria as desFribed earlier. The
;-ray diIIraFtion patterns shown in )igure 3.3 (F) and the peaks assigned are
tabulated in Table 3.3. Meanwhile, Ior the =r.7Ce.322 Fatalyst prepared in 5 mL
oI water, it Fan be observed that the monoFliniF phase oI =r22 has totally reduFed
and the Iormation oI tetragonal =r22 phase still remained as the dominant phase.
The diIIraFtogram Ior =r.5Ce.522 sample that was prepared by using 5mL
oI water is given as a representative in )igure 3.3 (e) Ior Fomparison. It showed that
the degree oI Frystallinity had deFreased and the sample is observed to be highly
amorphous with small partiFles present in the material (as shown in Table 3.4).
2verall, it is shown that the ;RD peaks gradually shiIted to a lower 2ș values
as a IunFtion oI inFreased Ferium loading. Ceria plays a major role as Fation dopant
to retard the Iormation oI monoFliniF phase oI =r22. :hen the Fontent oI =r is eTual
to or less than 5, the Fatalysts show FubiF Iluorite ;RD patterns similar to that oI
the host o[ide Feria. At =r Fontent higher than 5, ]irFonia beFomes the host o[ide
and the resulting Fatalyst show FharaFteristiF oI a tetragonal phase >67@.
The partiFle si]es oI the Fatalyst samples prepared in 5 mL and mL oI water
with diIIerent loading oI Feria were FalFulated using SFherrer Iormula shown in
Appendi[ A and are tabulated in Table 3.4 Ior Fomparison. )rom these data, it is
observed that Fatalyst sample prepared in greater amount oI water possessed a larger
partiFle si]e. Besides, it also shows that Fatalyst samples with higher loading oI Feria
have a smaller partiFle si]e.
3
(a) =r.95Ce.522
Intensity
(b) =r.9Ce.122
(F) =r.Ce.222
(d) =r.7Ce.322
(e) =r.5Ce.522
1
2
3
4
5
6
7
2ș (ž)
=r22 (t)
)igure 3.3
=r22 (m)
DiIIraFtograms oI =r[Ce1-[22 Fatalyst with diIIerent amount oI Feria
in 5 mL oI water (a) =r.95Ce.522, (b) =r.9Ce.122,
(F) =r.Ce.222, d) =r.7Ce.322, and (e) =r.5Ce.522
39
Table 3.3
;RD peaks assignment Ior =r[Ce[-122 Fatalysts in 5 mL oI water
Sample
2ș Angle
=r.95Ce.522
=r.9Ce.122
=r.Ce.222
=r.7Ce.322
=r.5Ce.522
*
m
d (c)
ReIerenFe
Peaks
d (c)
Assignment
2.2
3.15
3.16
=r22 (m)
3.175
2.96
2.95
=r22 (t)
31.474
2.4
2.4
=r22 (m)
35.123
2.55
2.54
=r22 (t)
5.211
1.2
1.1
=r22 (t)
6.9
1.54
1.54
=r22 (t)
2.363
3.14
3.16
=r22 (m)
3.196
2.96
2.95
=r22 (t)
31.49
2.4
2.4
=r22 (m)
35.1
2.55
2.54
=r22 (t)
5.252
1.1
1.1
=r22 (t)
6.19
1.54
1.54
=r22 (t)
2.34
3.15
3.16
=r22 (m)
29.924
2.9
2.95
=r22 (t)
31.191
2.7
2.4
=r22 (m)
34.739
2.5
2.54
=r22 (t)
49.3
1.3
1.1
=r22 (t)
59.25
1.56
1.54
=r22 (t)
29.955
2.9
2.95
=r22 (t)
34.69
2.5
2.54
=r22 (t)
49.71
1.3
1.1
=r22 (t)
59.2
1.56
1.54
=r22 (t)
59.427
1.55
1.55
=r22 (t)
29.442
3.3
2.95
=r22 (t)
34.21
2.63
2.54
=r22 (t)
49.145
1.5
1.1
=r22 (t)
57.659
1.6
1.54
=r22 (t)
monoFliniF phase
t
tetragonal phase
4
Table 3.4
PartiFle si]es oI the sample with diIIerent amount oI Feria perFentage
in 5 mL and mL oI water FalFined at 4 žC
PartiFle Si]es (nm)
Sample
3.1.3
5 mL oI water
mL oI water
=r.95Ce.522
1.9
19.75
=r.9Ce.122
17.5
2.31
=r.Ce.222
17.4
1.76
=r.7Ce.322
12.9
14.36
=r.5Ce.522
6.1
-
Effect of Calcination Temperature on the Formation of Tetragonal
Phase ZrO2 in Zr0.70Ce0.30O2 Catalyst
Based on the =r.7Ce.322 sample prepared in 5 mL and mL oI water were
seleFted in order to study the eIIeFt oI the FalFination temperature on the Iormation
oI tetragonal =r22 phase. The ;RD pattern oI =r.7Ce.322 sample in 5 mL oI
water under the heat treatment at 7 žC, 4 žC and 6 žC are Fomparatively shown
in )igure 3.4 and peak assigned are tabulated in Table 3.5. The =r.7Ce.322 sample
dried at 7 žC resulted an amorphous nature with small partiFles present.
As the FalFination temperature inFreased to 4 žC, there was a distinFt
sharpening and inFrease in intensity oI the peaks at 2ș values oI 29.355, 49.71,
59.2, 59.427 and 34.69 ž or d-spaFing values oI 2.9, 1.3, 1.56, 1.55 and 2.5 c
(PD) >66@ d-spaFing values (c): 2.95, 1.1, 1.54, 1.55 and 2.54) whiFh are assigned
to tetragonal =r22 phase were observed. No other peak is deteFtable in the
diIIraFtogram pattern at this FalFination temperature. At this FalFination temperature,
it Fan be observed that the e[istenFe oI tetragonal =r22 phase as the main phase in
the sample. However, Iurther FalFination at 6 žC, the presenFe oI a very low
intensity oI peaks due to the monoFliniF =r22 phase was observed with 2ș values at
appro[imately 2.531 and 31.224 ž or d-spaFing values oI 3.15 and 2.6 c (PD) >66@
d-spaFing values (c): 3.16 and 2.4). At the temperature oI 6 žC, tetragonal phase
41
oI =r22 still remained as the dominant phase with 2ș values oI 29.913, 49.699,
49.5, 5.5, 5.53 and 34.2 or d-spaFing values oI 2.9, 1.3, 1.4, 1.2, 1.5
and 2.57 c (PD) >66@ d-spaFing values (c): 2.95, 1.1, 1., 1.2, 1.54 and 2.56). It
is shown that the monoFliniF =r22 phase inFreased in intensity as the FalFination
temperatures inFreased, but the three highest peaks still due to the Iormation oI
tetragonal =r22 phase. It Fan be FonFluded that this amount oI Ferium loading as the
main eIIeFt on the Iormation oI tetragonal =r22 phase in =r[Ce1-[22 Fatalyst. The
amount oI Feria loading Fan stabili]e the Iormation oI single-phase tetragonal =r22
in the =r22-Ce22 mi[ed o[ides Fatalyst material.
Similar result was obtained Ior the =r.7Ce.322 sample prepared in mL oI
water and FalFined at 4 žC ()igure 3.5 and Table 3.5) with the present oI tetragonal
=r22 phase at 2ș values oI 29.2, 49.515, 49.9, 59.146 and 34.562 ž or d-spaFing
values oI 2.99, 1.4, 1.3, 1.56 and 2.59 c (PD) >66@ d-spaFing values (c): 2.95,
1.1, 1., 1.54 and 2.54) were observed as the main phase. Again, Iurther
FalFination at 6 žC, the presenFe oI a very low intensity oI peaks due to the
monoFliniF =r22 phase was observed.
AFFording to the ;RD patterns oI =r.7Ce.322 sample shown in )igure 3.4
and )igure 3.5 with an inFreasing in the amount oI Feria Fontent, the ;RD peaks
gradually shiIted to a lower 2ș values. This is due to the inFrement in the
Fomposition oI Feria in the Fatalyst material, thus aIIeFted the matri[ oI the Fatalyst
material. The larger ioniF radius oI Ce4 (.97 c) than =r4 (.4 c) involves an
inFrease oI the lattiFe Fonstant and the FonseTuent shiIt oI the diIIraFtion peaks
towards lower 2ș values >42@. At 4 žC, the main phase is due to the tetragonal
phase oI =r22, but when the temperature inFreased, the monoFliniF phases oI =r22
inFreased as well. This indiFated that at higher FalFination temperature (6 žC),
both tetragonal and monoFliniF phases were Foe[isted with the tetragonal phase
being more prominent at eaFh temperature. The degree oI Frystallinity was also
observed Irom the peak intensity and peak broadening in the diIIraFtogram pattern
obtained. In general, broad and low intensity peaks oI the diIIraFtogram pattern Ior
sample treated at 7 žC showed the sample to be amorphous with small partiFles
present in the material. As the FalFination temperature inFreased, the degree oI
42
Frystallinity inFreased as well. InFrement in Frystallinity and growth in Frystallite
si]e were observed by heat treatment at 4 žC and 6 žC as shown in Table 3.5.
(F) =r.7Ce.322
FalFined at 6 ÛC
Intensity
(b) =r.7Ce.322
FalFined at 4 ÛC
(a) =r.7Ce.322
dried at 7 ÛC
1
2
3
4
5
6
7
2ș (ž)
=r22 (t)
)igure 3.4
=r22 (m)
DiIIraFtograms oI =r.7Ce.322 prepared using 5 mL oI water dried
at (a) 7 žC, and FalFined at (b) 4 žC and (F) 6 žC
43
(b) =r.7Ce.322
FalFined at 6 ÛC
Intensity
(a) =r.7Ce.322
FalFined at 4 ÛC
1
2
3
4
5
6
7
2ș (ž)
=r22 (t)
)igure 3.5
=r22 (m)
DiIIraFtograms oI =r.7Ce.322 prepared using mL oI water and
FalFined at (a) 4 žC and (b) 6 žC
44
Table 3.5
;RD peaks assignment Ior =r.7Ce.322 Fatalyst prepared in 5 mL
and mL oI water FalFined at 4 žC and 6 žC
CalFination Temperature (žC)
4
Sample
2ș (žC)
ReIerenFe
Peak
d (c)
d (c)
Assignment
6
d (c)
Angle
2ș (žC)
Angle
-
-
2.351
3.15
3.16
=r22 (m)
29.955
2.9
29.913
2.9
2.95
=r22 (t)
-
-
31.224
2.6
2.4
=r22 (m)
34.69
2.5
34.2
2.57
2.54
=r22 (t)
=r.7Ce.322
-
-
49.5
1.4
1.
=r22 (t)
(5 mL)
49.71
1.3
49.699
1.3
1.1
=r22 (t)
59.2
1.56
5.53
1.5
1.54
=r22 (t)
59.427
1.55
-
-
1.55
=r22 (t)
-
-
2.221
3.16
3.16
=r22 (m)
29.2
2.99
29.6
3.
2.95
=r22 (t)
34.562
2.59
34.612
2.59
2.54
=r22 (t)
=r.7Ce.322
49.515
1.4
49.47
1.4
1.1
=r22 (t)
( mL)
49.9
1.3
49.
1.3
1.
=r22 (t)
-
-
5.55
1.5
1.55
=r22 (t)
59.146
1.56
59.2
1.56
1.54
=r22 (t)
The diIIraFtograms Ior =r.9Ce.122 and =r.Ce.222 Fatalysts FalFined at
4 žC and 6 žC are shown in Appendi[ C D respeFtively Ior Fomparison. )or
the =r.9Ce.122 Fatalyst as shown in Appendi[ C, it is obvious that the inFreasing
oI FalFinations temperature Faused the inFrement in intensity oI the monoFliniF phase
=r22. However, the intensity oI the monoFliniF =r22 phase in =r.Ce.222 Fatalyst
as shown in Appendi[ D is lower than the =r.9Ce.122 Fatalyst even at the same
FalFination temperature (6 žC). It Fan be FonFluded that the amount oI Feria
loading play a role to Fontrol the intensity oI monoFliniF phases in Fatalyst.
45
)rom Table 3.6, the partiFle si]es oI =r.7Ce.322 sample inFreased
relatively to the FalFination temperature and the amount oI water. )or the sample
that was prepared by using mL oI water, the partiFle si]e that was FalFined at
6 žC (15.25 nm) is slightly larger than the sample FalFined at 4 žC (14.36 nm).
This same trend is appliFable to the sample that is prepared by using 5 mL oI water.
Its partiFle si]e at FalFination temperature oI 6 žC is 13.5 nm while at 4 žC is
12.9 nm. However, at same FalFination temperature, the partiFle oI =r.7Ce.322
sample that was prepared by using 5 mL oI water is smaller Fompared to the one
prepared by using mL oI water. The results showed that the partiFle si]e is larger
at higher FalFination temperature and greater amount oI water.
Besides ;RD analysis, surIaFe area analysis was Farried out to determine the
surIaFe area Ior the =r.7Ce.322 prepared in 5 mL and mL oI water FalFined at
4 žC and 6 žC. The surIaFe area Ior =r.7Ce.322 samples are tabulated in
Table 3.6. )or the sample that was prepared by using mL oI water, the surIaFe area
at FalFination temperature oI 4 žC is 39.73 m2/g while at 6 žC is
14. m2/g. Meanwhile, the surIaFe area Ior the sample prepared with 5 mL oI water
FalFined at 4 žC is 35.36 m2/g whereas at 6 žC is 14.15 m2/g. )rom these data,
when the FalFination temperature inFreased, it is known that the surIaFe area will
deFrease while the partiFle si]e inFrease. This is due to the sintering proFess takes
plaFes as the treatment temperature inFreases Iorming larger partiFles with a smaller
surIaFe area. However, the surIaFe area does not inFrease relatively with the
deFreasing in partiFle si]e. This probably due to the present oI diIIerent shape oI
pores in the Fatalyst, whiFh Fan be proven by the pore te[ture analysis. )or Fatalysis
purposes, it is important that the aFtive phase is present in the highest FonFentration
possible and with the highest surIaFe area (small dispersed partiFles) on the support
surIaFe in order to ma[imi]e the aFtivity >36@.
46
Table 3.6
PartiFle si]es and surIaFe area oI =r.7Ce.322 Fatalysts prepared in 5
mL and mL oI water FalFined at 4 žC and 6 žC
Amount oI water (mL)
mL
5 mL
CalFination Temperature (žC)
4
6
4
6
PartiFle Si]e (nm)
14.36
15.25
12.9
13.5
39.73
14.
35.36
14.15
2
SurIaFe Area (m /g)
3.2
Fourier Transform Infrared (FTIR) Analysis
)rom the results oI ;RD analysis that was Farried out on various Fatalysts
with diIIerent loading oI Feria, it is Iound that =r.7Ce.322 Fatalyst prepared in
5 mL oI water gives the optimum Fondition Ior the Iormation oI single phase
tetragonal =r22. Thus, this typiFal Fatalyst is seleFted Ior Iurther study by using
)ourier TransIorm InIrared ()TIR) Analysis. The )TIR speFtrum oI prepared
sample dried at 7 žC is depiFted in )igure 3.6 whereas Ior the sample FalFined at
4 žC and 6 žC are depiFted in )igure 3.7 and )igure 3. respeFtively.
)rom the )TIR speFtrum oI =r.7Ce.322 dried at 7 žC, a broad 2-H
stretFhing band due to the adsorbed moleFular water Fan be observed in the range oI
36 Fm-1 to 25 Fm-1 with the ma[imum given at 321. Fm±1. The band that is
assigned to water deIormation mode is observed at 1634.6 Fm±1. Nitrate Fan also be
deteFted at 1335.6 Fm-1 whereas the band due to hydro[yl deIormation mode oI
surIaFe hydro[yl groups is deteFted at 137.6 Fm-1. Two bands are deteFted at
666.4 Fm-1 and 497.6 Fm±1. These two bands are assigned to the M-2 stretFhing
mode oI =r-2.
47
T
wavenumber (Fm-1)
)igure 3.6
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared in 5 mL oI water
dried at 7 žC
The )TIR speFtrum Ior the sample FalFined at 4 žC is shown in
)igure 3.7. A small peak has been deteFted at 3321.2 Fm-1. This band is assigned to
the unsymmetriFal 2H stretFhing Irom adsorbed moleFular water whereas the water
deIormation mode has reduFed. A broad band has also been deteFted at 459. Fm±1.
This band is assigned to the =r-2 (M-2) stretFhing band and has shiIted to a lower
wave number Fompared to the sample dried at 7 žC.
4
137.6
T
wavenumber (Fm-1)
)igure 3.7
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared in 5 mL oI water
FalFined at 4 žC
)urther FalFination temperature at 6 žC, a broad peak assigned to the
=r-2 (M-2) stretFhing band has been deteFted at lower wave number oI 453.2 Fm±1.
A small additional peak is also been deteFted at 655. Fm-1 Fompared to the sample
FalFined at 4 žC. This most probably due to the interIerenFe oI Ferium o[ide phase
in the =r22 matriFes. It is indiFated that the =r-2-=r stretFhing band originally at
735 Fm-1 >53@ has aIIeFted by the presenFe oI Feria in the material. It is also indiFated
that the band has shiIted to lower wave number as the FalFination temperature
inFrease. This is beFause most oI the speFies at the surIaFe oI Fatalyst espeFially ±
2H is eliminated with the inFreasing FalFination temperature. As a result, =r-2 bond
will beFome stronger with better Frystallinity. The result Irom the )TIR analysis is
in good agreement to the ;RD analysis Ior =r.7Ce.322 FalFined at 4 žC and
6 žC.
49
137.6
T
wavenumber (Fm-1)
)igure 3.
)TIR speFtrum oI =r.7Ce.322 Fatalyst prepared in 5 mL oI water
FalFined at 6 žC
3.3
Catalytic Activity of Zr0.70Ce0.30O2 Catalyst Towards Carbon Monoxide
Oxidation Reaction
)rom the result oI ;RD and )TIR analysis, it Fan be observed that the
Fatalyst with the atomiF perFentage ratio oI =r.7 : Ce.3 FalFined at 4 žC showed
the optimum Fondition on the Iormation oI single phase tetragonal =r22. Thus,
=r.7Ce.322 Fatalyst prepared in 5 mL and mL oI water were seleFted Ior Iurther
study on the FatalytiF aFtivity towards Farbon mono[ide Fonversion. The results are
disFussed based on the Light-2II Temperature (TL2) and 1 Fonversion
temperature (T1), as summari]ed in Table 3.7. The =r.7Ce.322 Fatalyst prepared
in 5 mL oI water and FalFined at 4 žC showed a better perIormanFe towards the
Fonversion oI C2 Fompared to the Fatalyst prepared in mL oI water. This Fatalyst
5
showed a low TL2 value at room temperature while 1 C2 Fonversion was
aFhieved at T1
32 žC whereas Ior the =r.7Ce.322 Fatalyst prepared in
mL oI water also showed a low TL2 value at room temperature. It gave only
3.1 Fonversion oI C2 even at ma[imum temperature oI 4 žC.
Table 3.7
* RT
CatalytiF aFtivity oI =r.7Ce.322 Fatalyst towards C2 Fonversion
=r.7Ce.322 Catalyst
TL2 ( žC)
T1 ( žC)
5 mL
RT *
32
mL
RT *
4 (3.1)
Room Temperature (25 ± 3 žC)
TL2
Light-2II Temperature
T1
1 C2 Conversion Temperature
Plots oI perFentage Fonversion oI C2 versus temperature Ior the
=r.7Ce.322 Fatalysts prepared in diIIerent amount oI water are shown in
)igure 3.9. )or the =r.7Ce.222 Fatalyst prepared in 5 mL oI water, it Fan be
observed that C2 Fonversion inFreases sharply at Light-2II temperature. Conversion
oI C2 remained at the same perFentage within the region oI 3 ± 2 žC. The
Fonversion inFreases gradually aIter 2 žC and 1 oI C2 Fonversion was
aFhieved at 32 žC whereas the Fonversion oI C2 Ior the =r.7Ce.322 Fatalyst
prepared in mL oI water only inFreases slightly aIter the TL2 and did not give 1
oI Fonversion even at ma[imum temperature oI 4 žC. It Fan be FonFluded that
the =r.7Ce.322 Fatalyst prepared in 5 mL oI water and FalFined at 4 žC showed a
better perIormanFe towards the Fonversion oI C2 with 1 Fonversion
temperature (T1) Fompared to the Fatalyst prepared in mL oI water. This
probably due to lower degree oI Frystallinity Ior the =r.7Ce.322 Fatalyst prepared
in 5 mL oI water, whiFh possesses a lot oI deIeFt sites and thus gave a better
perIormanFe towards C2 o[idation Fompared to the Fatalyst prepared in mL oI
water with higher degree oI Frystallinity. It Fan be FonFluded that the C2 o[idation
not solely depends on the tetragonal phase but the degree oI Frystallinity. This
FatalytiF result is in agreement with the result obtained in the ;RD analysis oI the
good perIormanFe Fatalyst.
51
=r.7Ce.322 (mL)
=r.7Ce.322 (5mL)
12
Conversion oI C2 ()
1
6
4
2
1
2
3
4
Temperature (žC)
)igure 3.9
PerFentage Fonversion oI C2 versus temperature Ior the =r.7Ce.322
Fatalyst prepared in mL and 5 mL oI water
CHAPTER IV
CONCLUSIONS
4.1
Conclusions
This research found that the Zr0.70Ce0.30O2 catalyst prepared in 5 mL of water
by using zirconium oxychloride and cerium (III) nitrate hexahydrate as the
precursors, dried for two days at 70 ºC and calcined at 400 ºC for 17 hours gives the
optimum condition on the highest formation of single phase tetragonal ZrO2.
The XRD analysis showed that this catalyst has some degree of crystallinity
property, consists of the tetragonal ZrO2 as the main phase and average crystalline
size of approximately 12.98 nm serve as the active phases for the catalyst. The
particle size increased as the amount of water increased while the particle size
decreased as the amount of ceria increased. The role of ceria is to retard the sintering
process as well as the present of monoclinic ZrO2 phase. At 400 ºC, the main phase
is tetragonal but when the temperature increased, the tetragonal phase slightly
decreased with an increase in the monoclinic phase. Surface area analysis showed
this catalyst has 35.36 m2/g of surface area. This surface area decreased as the
calcination temperature increased, which is in agreement with the enlargement of the
particle size.
53
FTIR analysis showed the existence of surface hydroxyl group on the surface
of catalyst. The bands assigned to the water deformation mode, hydroxyl
deformation mode of surface hydroxyl groups and nitrate has been totally diminished
as the calcination temperature increased. The position of the Zr-O (M-O) stretching
bands shifted to a lower wave number as the calcination temperature increased. At
400 ºC, the band at 459.0 cm-1 was assigned to the M-O stretching mode of ZrO2 has
shifted to a lower wave number at 453.2 cm-1 for further calcination temperature at
600 ºC. For the sample calcined at 600 ºC, a small additional peak was observed at
655.8 cm-1, this most probably due to the interference of cerium oxide phase in the
ZrO2 matrices. The Zr0.70Ce0.30O2 catalyst prepared in 5 mL of water and calcined at
400 ºC showed a better performance towards the conversion of CO with 100 %
conversion temperature (T100) compared to the catalyst prepared in 8 mL of water. It
gives the lowest TLO at room temperature while T100 at 320 ºC.
We can conclude that the amount of water used in this study did not show
significant effect on its physical properties but on the other hand, did affect its
catalytic performance.
4.2
Future Works
This research studied on the optimum condition / parameters on the formation
of tetragonal ZrO2 in the ZrO2-based catalyst doped with ceria. A further study need
to be carried out to fully utilize the results obtained from this research.
Since this research concentrated solely on the inorganic-based sol-gel method
that involved inorganic salt that easily dissolved in water, an organic-based sol-gel
method involving organometallic salts such as alkoxides that can be dissolved in
organic solvent should be carried out to compare the effect of precursors on the
formation of tetragonal ZrO2 phase in the ZrO2 based catalyst. Study on the amount
of solvent used should also be carried out further to see obvious changes on the
physical properties of the catalyst material.
54
Other characterization techniques can be used for further understanding of the
properties of the catalyst. Nitrogen adsorption analysis at 77 K should be carried out
to determine the types and shapes of pores for catalysts. The chemical composition
of the prepared model catalysts can be analyzed with Auger electron spectroscopy
(AES) to characterize the surface species segregation compared with the bulk
composition. Besides, the catalyst systems can also be further analyzed with X-ray
photoelectron spectroscopy (XPS) to verify surface composition and elemental
oxidation states [35].
Finally, the catalytic activity of Zr0.70Ce0.30O2 catalyst towards the oxidation
of CO and hydrocarbon with the reduction of NOx is suggested to carry out in order
to get better performance of the three-way catalyst.
55
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