MODIFIED MANGANESE OXIDE OCTAHEDRAL MOLECULAR SIEVES

FOR OXIDATION AND CONSECUTIVE OXIDATION-ACID

REACTIONS

FITRI HAYATI DARMALIS

UNIVERSITI TEKNOLOGI MALAYSIA

MODIFIED MANGANESE OXIDE OCTAHEDRAL MOLECULAR SIEVES

FOR OXIDATION AND CONSECUTIVE OXIDATION-ACID

REACTIONS

FITRI HAYATI DARMALIS

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Doctor of Philosophy (Chemistry)

Faculty of Science

Universiti Teknologi Malaysia

DECEMBER 2009

iii

To my husband, Dr. Hendriyawan To my mother, Raidas

To my father, Darmalis To my sons: Faizan Munawwar Alfindri and Muhammad Husein Murtaza

For my Brothers: Yon Elfi, Joni Indra, Yalmasri and Khairul Arif

iv

ACKNOWLEDGEMENTS

Bismillahirrahmanirrahim In the name of Allah, the Most Gracious, the Most Merciful

All praise to be Allah, the supreme Lord of the world. May peace and blessings to Rasulullah Muhammad Shollallahu’ Alaihi Wassalam, all the prophets, his families, his close friends and all Muslims.

Firstly, I wish to express my deep sincere appreciation to my supervisors Prof

Dr. Halimaton Hamdan and Assoc. Prof. Dr. Hadi Nur, for their gratitude, encouragement, friendly advice, earnest guidance, and motivation. Without continuous support and curiosity from my supervisors, this thesis would not have been the same as presented here. I am also indebted to UTM and research grant from the Ministry of Science Technology and Innovation Malaysia (MOSTI) for funding my Ph.D. study under VOT number 74506. This support is gratefully acknowledged.

I also would like to express my gratitude to all lecturers and researchers in

Department of Chemistry for their support and Ibnu Sina Institute for Fundamental Science Studies (IIS) for catalysts characterization. Special gratitude is addressed to Dr. Lee and my colleagues at Zeolite and Porous Materials Group (ZPMG), namely Mr. Izan, Mrs. Rozana, Mrs. Suryani and Miss. Hidayah and others for useful discussion and help. My sincere appreciation also extends to all my friends who have provided supports at various occasions especially Mrs. Rosyida Permatasari and Mrs. Suryani Alifah.

Last but not least, my gratitude goes to my caring family, my husband, my

mother and father, my mother and father (Allah Yarham) -in law, my son and my brothers. To Bapak Nur Anas Djamil, Ibu Sofiah Djamaris and Dr Hadi’s family. I thank you for continuous support, prayer, love, understanding and encouragement.

v

ABSTRACT

The research was focused on improvement of the catalytic activity of

octahedral manganese oxide molecular sieve (OMS-2) in oxidation and consecutive

oxidation-acid reactions. For oxidation reaction, OMS-2 was modified through

incorporation of metals and ion-exchange. Sulphation was applied in order to create

the acid sites on Ti-OMS-2 sample which was proven to have the highest oxidative

properties and tested for consecutive oxidation-acidic reaction. Ti, Fe, Co and Cu

were incorporated into the OMS-2 framework by isomorphous substitution to form

Ti-OMS-2, Fe-OMS-2, Co-OMS-2 and Cu-OMS-2, respectively. A new method to

synthesize Ti-OMS-2 with high Ti/Mn ratio was applied. Titanium incorporated

OMS-2 was successfully synthesized without addition of manganese (II) solution

which was normally necessary to synthesize metal substituted OMS-2. Ion-exchange

was carried out in order to replace K+ ion in the tunnel structure of OMS-2

framework by H+

ions using concentrated HNO3. Sulphation was done by

impregnation of certain amount of H2SO4 in different solvent. The characterization

results show that Ti-OMS-2 exhibited a significantly higher Lewis acidity compared

to the un-incorporated one. The physicochemical properties-catalytic activity of the

modified OMS-2 catalyst was studied in the oxidation of cyclohexane, cylohexene

and styrene, and also in consecutive transformation of 1-octene to 1,2-octanediol.

Oxidation of cyclohexane with TBHP as oxidant on transition metal substituted

OMS-2 showed that Ti-OMS-2 with high titanium content gave the highest

conversion, which may be due to the presence Ti sites in the framework and non-

framework. For metal incorporated in the framework, there is a correlation of ionic

radii of metal substituted with conversion of cyclohexane. An increase in ionic

radii of metal substituted OMS-2 increased the conversion of cyclohexane. This

correlation may be due to the increase in the Lewis acidity in the metal incorporated

OMS-2. The study on the catalytic activity of H-exchanged catalysts in oxidation of

cyclohexane showed an increase in conversion of cyclohexane after ion-exchange.

For further investigation, Ti-OMS-2 with high Ti/Mn ratio was used in oxidation of

cyclohexene and styrene using TBHP as oxidant. The results showed that both

titanium sites in framework and non-framework increased the activity of OMS-2 in

the oxidation of cyclohexene. However, it was observed that only non-framework

titanium species induced a synergetic effect that enhanced the oxidation of styrene.

There is a correlation between Ti site location in Ti-OMS-2 catalyst with activation

of C-H and C=C bonds. Ti sites in the framework only played role in C-H bond

activation whereas Ti site non-framework enhanced the catalytic activity for both

types of bond activation. SO42-

/Ti-OMS-2 was proven to be active for consecutive

transformation of 1-octene to 1,2-octanediol. However, it was confirmed that

Brönsted acid sites did not exist in the sample. The success of the consecutive

reactions may be due to the generation of Brönsted acid from hydrolysis of water on

the Lewis acid sites of SO42-

/Ti-OMS-2 sample.

vi

ABSTRAK

Penyelidikan difokuskan pada peningkatan aktiviti pemangkinan daripada penapis molekul oksida mangan oktahedral (OMS-2) sebagai mangkin dalam tindak balas pengoksidaan dan juga tindak balas berturutan pengoksidaan dan keasidan. Untuk tindak balas pengoksidaan, OMS-2 diubah suai melalui pemasukan logam dan pertukaran ion. Pensulfatan telah dilakukan untuk membina tapak asid pada mangkin Ti-OMS-2 yang terbukti mempunyai aktiviti pemangkinan paling tinggi dalam tindak balas pengoksidaan dan seterusnya diuji pada tindakbalas berturutan pengoksidaan dan keasidan. Ti, Fe, Co dan Cu dimasukkan ke dalam bingkaian OMS-2 melalui penukargantian isomorfus untuk membentuk Ti-OMS-2, Fe-OMS-2, Co-OMS-2 dan Cu-OMS-2. Satu kaedah baru telah digunakan untuk mensintesis Ti-OMS-2 pada nisbah Ti:Mn yang tinggi. Titanium yang digabungkan dengan OMS-2 telah berjaya disintesis tanpa penambahan larutan mangan(II) yang biasanya diperlukan untuk mensintesis penukargantian logam pada OMS-2 seperti yang dilaporkan sebelum ini. Penukaran ion telah dilakukan untuk menggantikan ion K+ didalam struktur terowong dengan ion H+ menggunakan HNO3 pekat. Pensulfatan telah dilakukan dengan pengisitepuan jumlah tertentu H2SO4 dalam pelarut yang berbeza. Hasil kaedah pencirian didapati bahawa penggabungan titanium kepada OMS-2 telah meningkatkan keasidan Lewis jika dibandingkan dengan OMS-2 sahaja. Pengoksidaan terhadap sikloheksana dengan TBHP sebagai agen pengoksidaan pada OMS-2 yang telah ditukarkan dengan logam peralihan memperlihatkan bahawa Ti-OMS-2 yang mempunyai kandungan titanium yang tinggi menghasilkan peratus penukaran yang paling tinggi, mungkin disebabkan oleh wujudnya tapak titanium dalam dan luar bingkaian. Untuk penggabungan logam di dalam bingkai, ada hubungkait antara jejari ion logam yang menukarganti dengan peratus penukaran sikloheksana. Peningkatan jejari ionik daripada logam yang menukarganti meningkatkan peratus penukaran sikloheksana. Hubungkait ini mungkin disebabkan oleh peningkatan tapak asid Lewis pada logam yang digabungkan dengan OMS-2. Kajian terhadap aktiviti pemangkinan ke atas mangkin tertukarganti H di dalam pengoksidaan menunjukkan peningkatan peratusan penukaran daripada sikloheksana setelah penukaran ion. Untuk kajian selanjutnya, Ti-OMS-2 dengan nisbah Ti:Mn yang lebih tinggi telah digunakan dalam pengoksidaan sikloheksena dan stirena dengan TBHP sebagai agen pengoksida. Didapati bahawa kedua-dua tapak titanium dalam dan luar bingkai meningkatkan aktiviti OMS-2 dalam pengoksidaan sikloheksena. Walau bagaimanapun, telah dibuktikan bahawa hanya spesies titanium bukan-bingkai sahaja menghasilkan kesan sinergi yang meningkatkan pengoksidaan stirena. Didapati bahawa wujud hubungkait antara lokasi tapak titanium pada mangkin Ti-OMS-2 dengan pengaktifan ikatan C-H dan C=C. Tapak titanium dalam bingkai memainkan peranan hanya untuk pengaktifan ikatan C-H sahaja sedangkan tapak titanium luar bingkai meningkatkan aktiviti pemangkinan pada kedua-dua jenis pengaktifan ikatan. Sampel SO4

2-/Ti-OMS-2 aktif untuk pertukaran berterusan 1-oktena kepada 1,2 oktanadiol. Bagaimanapun, telah dipastikan bahawa tidak ada tapak asid Brönsted pada sampel SO4

2-/Ti-OMS-2. Kejayaan daripada tindak balas berterusan tersebut mungkin disebabkan oleh pembentukan asid Brönsted daripada hidrolisis air yang terjadi pada tapak asid Lewis yang terdapat pada sampel SO4

2-/Ti-OMS-2.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xv

LIST OF SYMBOLS/ABBREVIATIONS xxi

LIST OF PUBLICATIONS xxiv

1 INTRODUCTION 1

1.1 Research Background 5

1.1.1 Porous Manganese Oxide Materials 5

1.1.2 Manganese Oxide Octahedral Molecular Sieves (OMS-2) 7

1.1.3 Modification of OMS-2 Materials 9

1.1.4 Designing of Sulfated Ti-OMS-2 as Bifunctional

Oxidative and Acidic Catalyst 12

1.2 Research Questions and Scope of the Research 13

1.3 Research Objectives 14

2 LITERATURE REVIEW 18

2.1 Introduction 18

2.2 Classification of Porous Manganese Oxide 18

viii

2.3 Material Synthesis 24

2.3.1 Synthesis of Porous Manganese Oxide 24

2.3.2 Synthesis of OMS-2 Materials 26

2.4 Modification of Manganese oxide 29

2.4.1 Overview of Modification of OMS-2 materials 29

2.4.2 Ion Exchange 37

2.4.3 Impregnation 38

2.4.4 Alkylsilylation 39

2.4.5 Sulphation 41

2.5 Catalytic Activity 42

2.5.1 Catalytic Activity of OMS-2 Materials 42

2.5.2 Catalytic Oxidation 45

2.5.3 Titanium Incorporated Materials 49

2.5.4 Sulphated Metal Oxides as a Solid Acid Catalyst 52

2.5.5 Synthesis of Diols 53

3 EXPERIMENTAL 55

3.1 Synthesis of OMS-2 Materials 55

3.1.1 Synthesis of OMS-2 without Buffer (OMS-2a) 57

3.1.2 Synthesis of OMS-2 with buffer (OMS-2b) 57

3.2 Modification of OMS-2 materials 57

3.2.1 Synthesis of Metal Substituted OMS-2 (M-OMS-2) 57

3.2.2 Ion Exchange of OMS-2 and M-OMS-2 Samples 58

3.2.3 Synthesis of Ti Incorporated OMS-2 (Ti-OMS-2) 59

3.2.4 Synthesis of Ti Impregnated OMS-2 [Ti-OMS-2 (imp)] 59

3.2.5 Preparation of TiO2-OMS-2 (mix) 59

3.2.6 Synthesis of Sulphated Ti-OMS-2 (SO42-/Ti-OMS-2) 60

3.2.7 Surface Modification by Alkylsilylation 60

3.3 Characterization Techniques 60

3.3.1 X-Ray Diffraction (XRD) Spectroscopy 61

3.3.2 Atomic Absorption Spectroscopy (AAS) 62

3.3.3 Fourier Transform Infrared (FTIR) Spectroscopy 63

3.3.4 Total Specific Surface Area (BET) and Pore Volume . ...

.....Analysis 65

ix

3.3.5 Thermal Gravimetry and Differential Thermal Analysis

......(TG-DTA) 67

3.3.6 Field Emission Electron Scanning Microscopy (FESEM) 68

3.3.7 Photoluminescence 68

3.3.8 X- Ray Photoelectron Spectroscopy (XPS) 70

3.3.9 Pyridine Adsorption 71

3.3.10 Adsorption Capacity of Adsorbed Water 74

3.3.11 Gas Chromatography (GC) Analysis 74

3.3.12 Gas Chromatography-Mass Spectrometry (GC-MS)

......Analysis 75

3.4 Catalytic Testing 75

3.4.1 Oxidation of Benzyl Alcohol 77

3.4.2 Oxidation of Cyclohexane 78

3.4.3 Oxidation of Cyclohexene 79

3.4.4 Oxidation of Styrene 80

3.4.5 Transformation of 1-octene to 1,2-octanediol 81

4 PHYSICOCHEMICAL PROPERTIES OF OMS-2 AND

MODIFIED OMS-2 CATALYSTS 83

4.1 Introduction 83

4.2 Physicochemical Properties of Prepared OMS-2 by Different

Methods 84

4.3 Physical Properties of Metal Substituted OMS-2 Material 92

4.3 Physical Properties of H-OMS-2 and H-M-OMS-2 Materials 102

4.4 Physicochemical Properties of Ti-OMS-2 Materials 106

4.4.1 Structural Properties of Ti Substituted OMS-2 Catalyst 106

4.4.2 Acidity Properties 113

4.4.3 Morphology, Surface Area and Textural Properties 114

4.4.4 Thermal Stability 119

4.4.5 More Evidence of the Location of Titanium on ...............

.....Ti-OMS-2 Materials 121

4.5 Alkylsilylated of OMS-2 and Ti-OMS-2(0.67) 127

4.6 Sulphated Ti-OMS-2 129

x

5 CATALYTIC ACTIVITY OF OMS-2 AND MODIFIED OMS-2

SAMPLE IN OXIDATION AND ACID REACTIONS 135

5.1 Introduction 135

5.2 Catalytic Activity and Selectivity of OMS-2 and Modified

OMS-2 Samples in Oxidation Reactions 135

5.2.1 Oxidation of Benzyl Alcohol over OMS-2 Prepared by

.....Different Method 135

5.3.2 Oxidation of Cyclohexane over Metals Substituted and

.....Ion.Exchanged OMS-2 140

5.4.3 Oxidation of Cyclohexene over Ti-OMS-2 Catalyst 150

5.4.2 Oxidation of Styrene over Different Location of

.....Titanium sites on Ti-OMS-2 Catalysts 152

5.3 The Effect of Lewis Acidity in Catalytic Oxidations 156

5.4 The Role of Different Location of Ti Sites in Ti-OMS-2 in

Oxidation Reactions 157

5.5 Catalytic Study on Consecutive Reaction of 1-octene to

1,2-octanediol 158

6 SUMMARY AND CONCLUSION 161

6.1 Summary 161

6.2 Conclusion 166

REFERENCES 171

APPENDIXES 189-199

xi

LIST OF TABLES

TABLE NO TITLE PAGE

1.1 The synthetic manganese oxides, their natural counterpart and

structures as reported by Suib [12, 20-22]. 7

1.2 The cations were doped OMS-2 and their location in OMS-2 material. 10

2.1 Classification of tunnel and layered manganese oxides and their

crystallographic data [13]. 19

2.2 Synthesis of tunnel and layered manganese oxides with various

templates. 26

2.3 Review of Metal Doped into OMS-2; its synthesis routes, location, properties, and catalytic application. 30

2.4 Some catalytic applications of OMS-2 materials reported in the last

decade. 42

2.5 Characteristic features of Shell’s epoxidation catalyst compared

with Titanium Silicalite 1. 49

2.6 The comparisons of the common mild oxidant are used in oxidation

process. 50

3.1 Position of bands and classification for linkages of pyridine. 72

4.1 Effect of potassium concentration in reflux method on the synthesis

of OMS-2. 85

4.2 The relative intensity and ratio of I(110)/I(200) plane of OMS-2b

and calcined OMS-2b samples calculated by XRD. 88

4.3 The ionic radii of metals ion and average crystallite size of OMS-2

and M-OMS-2 samples. 94

xii

4.4 Lattice parameter (a and c) and cell volume (V) of OMS-2 and M-

OMS-2 samples. 95

4.5 The relative intensity and ratio of I(110)/I(200) plane of OMS-2 and

M-OMS-2 samples. 96

4.6 The physical properties of metal ions. 97

4.7 Source of metal, its charge and their effect to cryptomelane

structure. 98

4.8 AAS data of OMS-2 and M-OMS-2 samples. 99

4.9 The relative intensity and ratio of I(200)/I(211) plane of OMS-2

and M-OMS-2 samples calculated by XRD. 102

4.10 The percentage of potassium substituted by H+. 104

4.11 Chemical composition and physicochemical properties of OMS-2,

Ti-OMS-2 and TiO2–OMS-2. 107

4.12 The lattice parameters (a and c) and cell volume (V) of OMS-2 and

Ti-OMS-2 samples. 109

4.13 Vibrational spectroscopy feature of samples. 111

4.14 The relative intensity and ratio of I(111)/I(211) plane of samples

calculated by XRD. 116

4.15 Binding Energies (eV) of Mn 2p, Ti 2p, and its line separation

(�BE) and difference of line separation from selected samples. 122

4.16 Assignments of as-observed IR bands on sulfated samples [154]. 131

5.1 Conversion of benzyl alcohol and selectivity to benzaldehyde by

different catalysts. 136

5.2 The relation of amount of potassium exchanged by H+ with

enhancement of % conversion of cyclohexane on H-M-OMS-2

catalyst. 144

5.3 The correlation of Lewis acidity of samples to conversion of

cyclohexane, cyclohexene and styrene. 156

xiii

5.4 The possible role of Lewis acids of catalyst in oxidation of

cyclohexane, cyclohexene and styrene. 157

5.5 The role of Ti sites location in oxidation reaction. 158

6.1 The physicochemical properties-catalytic activity relationship of the

catalysts. 163

xiv

LIST OF FIGURES

FIGURE NO TITLE PAGE

1.1 Steps Potential energy diagram for a catalytic reaction (solid

line), i.e. reaction of A and B to form AB, compared with the non-

catalytic reaction (dashed line). The presence of a catalyst

lowers the activation energy (Ea) considerably [7]. 2

1.2 Process options in catalytic oxidation and some of their

disadvantages. 3

1.3 Crystal structure of cryptomelane-type OMS-2: potassium atoms

are shown as green spheres; MnO6 octahedra are shown in brown. 8

1.4 Mars van Krevelen mechanism. 9

1.5 Partial periodic table showing transition metals that have been

introduced into OMS-2 materials. 10

1.6 Transformation of alkenes to diols via two step reaction. 12

1.7 The schematic of the research approach and research questions. 15

1.8 The significant of the use Ti-OMS-2 in heterogeneous oxidation

and acid reactions. 17

2.1 Schematic structures of one-dimensional tunnel and layered

manganese oxides [13]. 22

2.2 Intergrowth tunnels of (a) (1×1) and (1×2), and (b) (2×2) and

(2×3) in the tunnel manganese oxides. 23

2.3 Transformation reaction from birnessite to hollandite under

hydrothermal conditions. 28

2.4 The ion exchange reaction. 37

xv

2.5 Impregnation of porous catalyst. 38

2.6 Chemical structure of OTS. 39

2.7 Mechanism of complete reaction of OTS on the support surface

to form a well ordered layer. 40

2.8 Mechanism of incomplete reaction of OTS on the support surface. 40

2.9 Epoxidation of alkenes using (a) organic peracids, (b) chlorohyrins

route and (c) H2O2 or TBHP as the oxidant. 47

2.10 Epoxidation of propene on Shell catalyst using an organic

peroxide. 50

2.11 Oxidation reactions catalyzed by TS-1. 51

3.1 Materials preparation and their labelling. 56

3.2 The IUPAC classification for adsorption isotherms, where

nad = amount of adsorbed and P/Po= relative pressure. 66

3.3 The physical process following absorption of a photon by a

molecule. 69

3.4 The mechanism of interaction between pyridine molecules with

Lewis. 73

3.5 The interaction between pyridine molecules with Brönsted acid

sites.Catalytic reactions over various modified OMS-2. 73

3.6 Catalytic reactions over various modified OMS-2. 76

4.1 XRD patterns of OMS-2 materials and reference pattern of

Crypromelane, Q JCPDS 29, 1020. 86

4.2 Effect of calcination on XRD patterns of OMS-2b materials, (a)

before calcination, (b) calcination at 400oC, (c) at 500oC, and (d)

at 600oC. 88

4.3 FTIR spectra of (a) OMS-2a and (b) OMS-2b. 89

4.4 Defect on OMS-2 structure. 90

xvi

4.5 Amount of adsorbed water on the surface of OMS-2a and OMS-2b

samples. 90

4.6 TGA plots for OMS-2 materials in N2 atmosphere. 91

4.7 X-ray diffractograms of (a) OMS-2; (b) Ti-OMS-2(0.05); (c)

Fe-OMS-2(0.09); (d) Co-OMS-2(0.02); and (e) Cu-OMS-2(0.04). 93

4.8 Schematic incorporation of metals in M-OMS-2 materials. 93

4.9 XRD pattern of (a) cryptomelane and (b) Ti-, (c) Cu-, (d) Co- and

(e) Fe-OMS-2 was prepared by oxidation of its metal ions source

by potassium permanganate in acidic condition without the

addition of Mn2+ solution. 97

4.10 Morphology of OMS-2 and M-OMS-2 samples. 101

4.11 Schematic synthesis of H-OMS-2 and H-M-OMS-2. 102

4.12 XRD pattern of (a) OMS-2 and (b) H-OMS-2. 103

4.13 Morphology of H-OMS-2 and H-M-OMS-2 samples. 105

4.14 X-ray diffractograms of (a) cryptomelane (JCPDS 29, 102), (b)

OMS-2, (c) Ti-OMS-2 (0.18), (d) Ti-OMS-2 (0.43), (e) Ti-OMS-2

(0.67), (f) TiO2-OMS-2 (imp) and (g) Ti-OMS-2 (mix). 108

4.15 IR spectra at lower wavelength region of (a) OMS-2, (b)

Ti-OMS-2 (0.18), (c) Ti-OMS-2 (0.67). 110

4.16 IR spectra at higher wavelength region of (a) OMS-2, (b)

Ti-OMS-2 (0.18), (c) Ti-OMS-2 (0.67). 111

4.17 Photoluminescence spectra of OMS-2, Ti-OMS-2 (0.43) and

TiO2-OMS-2 (mix). The excitation wavelength is 430 nm. 113

4.18 FTIR spectra of (a) Ti-OMS-2 (0.67) and (b) OMS-2 after

evacuation under vacuum at 400 oC for 4 h followed by pyridine

adsorption at room temperature and evacuation at 150 oC for an

hour. 114

4.19 Morphology of (a) Ti-OMS-2 (0.18), (b) Ti-OMS-2 (0.18) and

(c) TiO2-OMS-2 (imp). 115

xvii

4.20 N2 adsorption isotherm for OMS-2 at 77 K. 116

4.21 N2 adsorption isotherm for (a) Ti-OMS-2(0.43) and (b)

Ti-OMS-2(0.67) at 77 K. 118

4.22 TGA profile (a) in original and (b) differential forms of OMS-2,

Ti-OMS-2 (0.18) and TiO2-OMS-2 (imp). 120

4.23 Detailed XPS spectra for the Mn 2p transition for (a) OMS-2, (b)

Ti-OMS-2(0.18), (c) Ti-OMS-2(0.67) and (d) TiO2-OMS-2(imp). 123

4.24 Bond strength on bridging oxygen atom. 125

4.25 Detailed XPS spectra for the Ti 2p transition for (a) Ti-OMS-2

(0.18), (b) Ti-OMS-2(0.67) and (c) TiO2-OMS-2(imp). 126

4.26 FTIR spectra of modified OTS samples (a) OTS/OMS-2 and (b)

OTS/Ti-OMS-2. 128

4.27 Percentage of adsorbed water on the sample (a) OMS-2, (b)

Ti-OMS-2(0.67), (c) OTS/Ti-OMS-2(0.67) and (d) OTS/OMS-2. 128

4.28 Proposed polymeric octadecylsiloxane on the surface of OMS-2

and Ti-OMS-2 samples. 129

4.29 XRD pattern of Ti-OMS-2(0.04) and sulphated Ti-OMS-2 (0.04).

# = TiOSO4.H2O,* = MnSO4 7H2O ¤ = MnSO4. 130

4.30 FTIR spectra of Ti-OMS-2 and sulphated Ti-OMS-2. 131

4.31 The bridging of bidentated structure of sulphated Ti-OMS-2. 132

4.32 Thermograms (TGA) of samples. 133

4.33 First derivative curves (DTGA) of samples. 133

4.34 FESEM micrograph of SW150-Ti-OMS-2(0.67) sample in

different magnitude. 134

5.1 The schematic reaction of benzyl alcohol to benzaldehyde. 136

5.2 Overall alcohol oxidation mechanism [24]. 139

5.3 Resonance model of Mn-O-Mn bond structure: Resonance

structure in crystalline OMS-2 (Structure A); and non-resonance

structure in amorphous materials (Structure B). 140

xviii

5.4 Schematic reaction of cyclohexane. 141

5.5 The conversion and product selectivity of oxidation of

cyclohexane with tert-butyl hydroperoxide (TBHP) using OMS-2,

M-OMS-2 and H-M-OMS-2. All reactions were carried out at

60 ºC for 24 h with cyclohexane (26 mmol), 70% aqueous TBHP

(10 mmol), and catalyst (50 mg) under reflux condition. 142

5.6 The relationship of ionic radii of metals substituted OMS-2 to

conversion of cyclohexane. 144

5.7 Yield of products vs time on Ti-OMS-2. 146

5.8 Homolytic pathway to form radical from TBHP over catalyst. 148

5.9 Formation of cyclohexyl hydroperoxide. 148

5.10 The heterolytic pathway of the formation of cyclohexanone from

cyclohexyl hydroperoxide. 148

5.11 The homolytic pathway of the formation of cyclohexanol from

cyclohexyl hydroperoxide. 149

5.12 The heterolytic pathway of the formation of cyclohexanol and

cyclohexanone from 1,4-dicyclohexyltetraoxidane. 149

5.13 Reaction condition of cyclohexene and its products. 150

5.14 The conversion and product selectivity of oxidation of

cyclohexene with tert-butyl hydroperoxide (TBHP) using TiO2,

OMS-2, Ti-OMS-2(0.18), and Ti-OMS-2(0.67). {All reactions

were carried out at 70 ºC for 2 h with cyclohexene (5 mmol), 70%

aqueous TBHP (10 mmol), acetonitrile (15 ml) and catalyst (50

mg). The conversion and the amount of product obtained in

blank experimental have been subtracted}. 151

5.15 Oxidation of styrene and its product on catalysts using TBHP as

oxidant. 153

5.16 The conversion and product selectivity of oxidation styrene with

tert-butyl hydroperoxide (TBHP) using TiO2, TiO2-OMS-2,

Ti-OMS-2, OMS-2 and TS-1. All reactions were carried out at

xix

70 oC with styrene (5 mmol), 70% aqueous TBHP (10 mmol),

acetonitrile (15 ml) and catalyst (50 mg) with vigorous stirring. 154

5.17 Consecutive oxidation and acid reaction to form of 1,2 octane diol

from 1-octene on sulphated Ti-OMS-2 catalyst. 159

5.18 Yield of epoxyoctane and 1,2 octane diol after 24 h reaction. 159

6.1 Assignments of modified OMS-2 in oxidation of cyclohexane and

consecutive reaction of 1-octene to 1,2 octanediol consecutive

reaction of 1-octene to 1,2 octanediol 167

6.2 The role of the location of Ti sites in Ti-OMS-2 in oxidation of

cyclohexane, cyclohexene and styrene. 169

xx

LIST OF SYMBOLS/ABBREVIATIONS

% - percent

~ - approximately

μ - micron (10-6)

2� - Bragg angle

Å - angstrom (10-10)

a.u. - arbitrary unit

BET - Brunnauer, Emmett and Teller

c.a. - about (Latin:circa)

cm-1 - per centimeter

Co2+ - Cobalt ion

Co-OMS-2 - Cobalt substituted OMS-2

Cu K� - X-ray diffraction from copper K� energy levels

Cu2+ - Copper ion

Cu-OMS-2 - Copper substituted OMS-2

d - distance

DTG - Differential thermogravimetry

e.g. - example (Latin: exempli gratia)

EDAX - Energy dispersive analysis by X-ray equilibrium pressure and vapour pressure Po of the adsorbate at the temperature where the isotherm is measured

et al. - and others (Latin: et alia)

eV - electrovolt

Fe3+ - Iron ion

Fe-OMS-2 - Iron substituted OMS-2

FESEM - Field Emission Scanning Electron Microscope

FID - Flame ionisation detector

FTIR - Fourier transform infrared

xxi

g - grams

h - hour

H2O2 - Hydrogen peroxide

HF - Hydrofluoric acid

i.e. - that is (Latin : id est)

IUPAC - International Union of Pure and Applied Chemistry

K - degree Kelvin

KBr - Potassium bromide

M - Molar

m2g-1 - meter square per gram

mA - milliampere

min - minute

mL - millilitre

mol - mole

M-OMS-2 - Metal substituted OMS-2

N2 - Molecular nitrogen

nm - nanometer (10-9) oC - degree celcius

OL-1 - OL-1 is manganese oxide Octahedral layered with interlayer spacing of ~7 Å.

OMS-1 - Manganese oxide octahedral molecular sieve with 3 x 3 tunnel structure.

OMS-2 - Manganese oxide octahedral molecular sieve with 2 x 2 tunnel structure.

OMS-5 - Manganese oxide octahedral molecular sieve with 2 x 4 tunnel structure.

OMS-6 - Manganese oxide octahedral molecular sieve with 2 x 3 tunnel structure.

OMS-7 - Manganese oxide octahedral molecular sieve with 1 x 1 tunnel structure.

OTS - Octadecyltrichlorosilane

P/Po - relative pressure; obtained by forming the ratio of the equilibrium pressure and vapour pressure po of the adsorbate at the temperature where the isotherm is measured

SO42-/Ti-OMS-2 - Sulphated Ti-OMS-2

ST150-Ti-OMS-2 - Sulphated Ti-OMS-2 with 150 �L concentrated H2SO4 using toluene as solvent

xxii

ST200-Ti-OMS-2 - Sulphated Ti-OMS-2 with 200 �L concentrated H2SO4 using toluene as solvent

SW150-Ti-OMS-2 - Sulphated Ti-OMS-2 with 150 �L concentrated H2SO4 using water as solvent

SW200-Ti-OMS-2 - Sulphated Ti-OMS-2 with 200 �L concentrated H2SO4 using toluene as solvent

t - crystallite size

TBHP - tert-butyl hydroperoxide

TGA - Thermogravimetry analysis Ti3+ - Titanium ion

TiO2 - Titanium dioxide

TiO2-OMS-2 (imp) - Impregnation of TiO2 on OMS-2 surface

TiO2-OMS-2 (mix) - Physical mixture of rutile TiO2 and OMS-2

Ti-OMS-2 - Titanium substituted OMS-2

TS-1 - Titanium Silicate-1

wt % - weight percentage

�� - wavelength

xxiii

LIST OF PUBLICATIONS AND PRESENTATIONS

1. H. Nur, F. Hayati, H. Hamdan, "On the location of different titanium sites in Ti-

OMS-2 and their catalytic role in oxidation of styrene", Catalysis

Communications, 8 (2007) 2007-2011.

2. F. Hayati, H. Nur, H. Hamdan, "Titanium Doped Octahedral Manganese Oxide

Hybrid Catalyst in the Oxidation of Cyclohexene", Buletin Kimia, 21 (2005) 49-

54.

3. F. Hayati, H. Hamdan, H. Nur, "Synergetic effect of titanium and OMS-2 as Ti-

OMS-2 hybrid catalyst in oxidation of cyclohexene", Book abstract of Annual

Fundamental Science Seminar 2005, 4-1 July 2005, Johor Bahru, Malaysia. p. 67.

4. F. Hayati, H. Nur and H. Hamdan, "Synthesis and characterization of octahedral

molecular sieves (OMS-2)", Book of abstract of Annual Fundamental Science

Seminar 2004, 14-15 June 2004, Johor Bahru, Malaysia. p. 73.

CHAPTER 1

INTRODUCTION

A catalyst is a substance which accelerates a chemical reaction. The basic

principle of how a catalyst works for a chemical reaction is shown by the example in

Figure 1.1. It does so by forming bonds with the reacting molecules (i.e. adsorption),

followed by breaking and weakening of the intramolecular bonds. Next, the

adsorbed species react on the surface to a particular product, often in several

consecutive steps. Finally, it detaches itself from the catalyst (i.e. desorption) and

leaves the catalyst unaltered so that it is ready to interact with the next set of

molecules. A catalyst cannot alter the chemical equilibrium of a given reaction; it

only creates a favourable reaction pathway. This is done by decreasing the activation

barrier (Ea,cat) compared to non catalytic reaction (Ea,non) and thus increasing the

reaction rate. In general, a successful catalyst increases the yield of the desired

product while decreasing that of other products, which has advantages for both

economic and environmental reasons [1].

The first introduction of the word ‘catalysis’ was by Berzelius in 1836, while

Ostwald presented the first correct definition of a catalyst in 1895 [2]. He described

a catalyst as a substance that changes the rate of a chemical reaction without itself

appearing in the products. Today, catalysis lies at the heart of our quality of life: the

reduced emissions of modern cars, the abundance of fresh food at our stores, and the

new pharmaceuticals that improve our health are made possible by chemical

reactions controlled by catalysts [3]. It covers multidisciplinary science that serves a

broad range of chemical industries covering specialty, fine, intermediate, commodity,

2

and life science chemicals [4]. It played a major role in establishing the economic

strength of the chemical and related industries in the first half of the 20th century and

an estimated 90% of all of the chemical processes introduced since 1930 depend on

catalysis [5]. According to a report from Freedonia [6] the world catalyst demand

will rise by 3.6% per year to $12.3 billion in 2010.

Figure 1.1: Potential energy diagram for a catalytic reaction (solid line), i.e. reaction

of A and B to form AB, compared with the non-catalytic reaction (dashed line). The

presence of a catalyst lowers the activation energy (Ea) considerably [7].

Catalysis plays an important role in the green chemical processes, which is to

minimize environmental impact and to reduce costs of the process. It is crucial to

achieve the “ideal synthesis” which would be atom efficient, safe, one step, involving

no wasted reagents, based on renewable resources, and environmentally acceptable

to overcome some of the biggest problem areas in synthetic methodology such as in

oxidation and acid-catalyze reactions [8].

In catalytic process, for example catalytic oxidation, there are some options to

consider, i.e. phase (gas or liquid) and catalytic system as shown in Figure 1.2.

Firstly, the selection of either a gas or liquid phase depends largely on the boiling

3

point and thermal stability of the reactants, especially of a desired fine chemical

intermediate. However, catalytic gas phase is limited to relatively simple molecules.

More complicated molecules cannot be brought easily into the gas phase and many

of these molecules are unstable at elevated temperatures. In addition, the gas phase

needs special reactor and costly. Therefore, working in liquid phase is relatively

easier than in gas phase, as simpler equipments are required which can be performed

for more complicated molecules.

Catalytic oxidation

Gas phase

� High temperature � Simple molecule only

�

Liquid phase

Homogeneous Heterogeneous

� �

Easy recovery and regeneration of catalyst

Most compounds not stable at elevated temperature

Low thermal stability

Difficulty of recovery and regeneration

Figure 1.2: Process options in catalytic oxidation and some of their disadvantages.

As also shown in Figure 1.2, another important choice to consider is whether

the oxidation should be performed using homogeneous or heterogeneous catalyst. In

homogeneous catalysis, the reaction mixture and the catalysts are all in the same

phase, usually the liquid phase. The catalyst may be a metal complex, which is

dissolved in a solvent together with the reagents. Homogeneous catalysts are

characterized by high activity and selectivity. The main advantage of homogeneous

catalysts is the ease of accessibility of the active site, resulting in a high activity, no

mass transfer limitations and generally low temperature and pressure requirements.

The main disadvantages of this type of catalysts are low thermal stability, difficulty

of recovery and regeneration. In combination with high cost of catalyst, this makes

homogeneous catalysis less popular in industry. Homogeneous catalysts are mostly

found in batch processes where volumes are small and the added value is high, e.g.,

in pharmaceuticals.

4

The problems faced by homogeneous catalyst can be solved by using

heterogeneous catalyst [1, 2, 5]. In heterogeneous catalysis, the catalyst is in a

different phase than the reaction mixture. Usually, the catalyst is a solid substance

(e.g., a metal or a metal oxide) and the reaction mixture can be a gas or a liquid.

Heterogeneous catalyst may be easily recovered by filtration and recycle. The

success of this type of catalyst is due to the ease at which it can be applied in all

types of reactions, carried out in both continuous and batch mode. It is relatively

easy to separate the catalyst from the reaction mixture and reuse it. The solid,

heterogeneous phase, however, may introduce mass transfer limitations, presumably

resulting in a lower activity or selectivity. Therefore, the selection of suitable active

site for heterogeneous catalyst is a challenge in academic and industry.

Many heterogeneous or solid catalysts are based on porous inorganic solids

[5]. The important physical properties of these materials are surface area (often very

large and measured in hundreds of m2/g), pore volume, pore size distribution (which

can be very narrow or very broad), the size and shape of the particles and their

strength. The solid catalyst provides a surface, usually large internal, for the

substrates to adsorb and react on. Thus the surface characteristics (roughness,

functional groups, organophilicity, hydrophobicity, etc.) are also vital to

performance.

Following the definition accepted by the International Union of Pure and

Applied Chemistry (IUPAC), porous materials can be grouped into three classes

based on their pore diameter (d): microporous, d < 2.0 nm; mesoporous, 2.0 < d < 50

nm; macroporous, d > 50 nm. In the class of microporous materials, zeolites and

related materials such as aluminophosphates have found for a long time applications

outside the traditional areas of acid and bifunctional catalysis [9-14]. With the

introduction of the ordered micelle-templated inorganic materials, the choice of

available supports has been considerably extended into the mesoporous domain.

Examples are M41S groups materials such as MCM-41, MCM-48, MSU, HMS,

FSM-16, and various SBA type materials [9, 10]. Macroporous metal oxides such

as titania, zirconia and alumina are example for macroporous material. However, all

of the above materials in general are insulating materials. In addition they are often

5

synthesized with charge compensation in mind. For example, Al3+ substituted for

Si4+ in zeolites lead to an inherent cation-exchanged capacity.

Another way to approach the generation of microporous material is to

generate element with mixed valencies in a structure which should also lead to cation

exchange capacity [11]. Porous manganese oxides with mixed valencies could be a

challenge due to wider application over aluminosilicate materials e.g. redox catalysis,

battery and sensor [12].

1.1 Research Background

1.1.1 Porous Manganese Oxide Materials

Porous manganese oxide is one of the largest families of porous materials.

These are two major structures of porous manganese oxides, tunneled and layered

materials with pore size from ultra-micropores to mesopores [13]. Natural

manganese oxides are found abundant as manganese nodules which exist in a wide

variety of locations such as the ocean floor, the beds of many fresh-water lakes,

rocks, and soil. Manganese oxide minerals have been used for thousands of years as

pigments and to clarify glass, and more recently as ores of Mn metal, catalysts and

battery material [14].

Porous manganese oxide materials have been described as useful catalysts in

the oxidation of carbon monoxide, methane and butane, the reduction of nitric oxide

with ammonia and demetallation of topped crude in the presence of hydrogen [15].

However, the structures and properties of the natural source are usually not uniform

and its activity is not reproducible.

The porous manganese oxides have been extensively investigated for their

economic value and their potential applications. Due to their excellent cation-

exchange and molecule adsorptive properties, like the aluminosilicates, these

6

manganese oxides can be used as ion-sieves, molecular-sieves, and catalysts similar

to the aluminosilicates. In contrast to aluminosilicate based zeolite, these manganese

oxides are mixed valencies materials (mainly, 4+, 3+, or 2+). The mixed valency

materials are important in biology, chemistry, and physics which occur in manganese

redox enzymes, in natural manganese oxide nodules, chemiluminescence systems,

electron transfer and electrocatalysis, electrochromism, secondary nonaqueous

rechargeable batteries, magnetics, ceramics, and biological systems. In chemistry,

mixed valency in mixed metal oxides is important for electron transport. For

example, the effectiveness of metal oxides as catalysts for redox reactions, as

electrode materials for electrochemical processes, and as chemical sensors for

reductive gases are usually governed by their ability and tendency to cycle between

different valence states of relevant cations and the mobility of oxygen ions. From

this standpoint, manganese oxide materials have distinct advantages over

aluminosilicate molecular sieve materials for applications in redox catalysis,

batteries, and chemical sensors [12].

The synthetic manganese oxides have been intensively studied by Suib and

his group since 1990’s[16-18]. The synthetic names, the natural minerals and unit

structures are listed in Table 1.1. In general manganese oxide materials can be

classified into two kinds i.e. tunnel and layered structures. The term of octahedral

molecular sieves (OMS) and octahedral layered (OL) materials are referred to the

synthetic manganese oxides with tunnel and layered structure, respectively [19].

OMS materials comprise infinite 3-D crystalline frameworks with molecule-sized

tunnels similar to the naturally occurring zeolites. The structural frameworks of the

manganese oxides consists of MnO6 octahedral units shared by corners and/or edges

in comparison with, in general, SiO4-AlO6 frameworks of the porous

aluminosilicates. OMS-1 and OMS-2 are two types of OMS materials which are

built of 3x3 and 2x2 MnO6 octahedral units, respectively. The other types are

pyrolusite-, ramsdellite-, and romanechite-type manganese oxides which have one-

dimensional (1×1), (1×2) and (2×3) tunnel structures, respectively. OL materials

have interlayer spacings that are similar to clay-type materials. OL-1 is synthetic

name of birnessite which has the interlayer spacing of ~7 Å and it contains

exchangeable cations and water molecules.

7

Table 1.1: The synthetic manganese oxides, their natural counterpart and structures

as reported by Suib [12, 20-22].

Synthetic Name Natural counterpart MnO6 octahedral units

OMS-1 todorokite 3x3

OMS-2 cryptomelane 2x2

OMS-5 - 2x4

OMS-6 romanechite 2x3

OMS-7 pyrolusite 1x1

OL-1 birnessite 2x~

Among most of the OMS and OL materials, OMS-1 and OMS-2 materials

have been used widely as catalysts, chemical sensors and batteries due to their

mixed-valency, high porosity, thermal stability, surface areas, and inexpensive

manufacturing cost. However, OMS-2 materials have been used as catalyst even

more widely than OMS-1 materials since they are more active and selective in

catalytic oxidation [20].

1.1.2 Manganese Oxide Octahedral Molecular Sieves (OMS-2)

As mentioned before OMS-2 materials are synthetic manganese oxide which

is built of 2x2 MnO6 octahedral and also known as synthetic cryptomelane [11]. The

tunnel size of this material is 4.6 Å x 4.6 Å and potassium ion exists in the tunnel to

balance the charge of the structure as shown in Figure 1.3. General composition of

OMS-2 materials is K0.8–1.5Mn8O16. These materials are not expensive and easy to

prepare compared to other manganese oxide type materials.

For its application in catalytic reaction, OMS-2 materials were reported to be

selective in oxidation of benzyl alcohol [23, 24]. Besides, OMS-2 materials are

potential electrocatalysts for the oxidation of methanol, for fuel cell applications

8

[25], are also active catalyst for the total oxidation of benzene and ethanol [26] and

epoxidation of olefins [27, 28]. The mild oxidants i.e. molecular oxygen and ter-

butyl hydrogen peroxide (TBHP) used as oxidizing agents on OMS-2 materials have

let to these materials being promising catalysts in fulfilling the environmental

concern and regulations for clean environment.

Figure 1.3: Crystal structure of cryptomelane-type OMS-2: potassium atoms are

shown as green spheres; MnO6 octahedra are shown in brown.

The high oxidation ability of OMS-2 materials has mainly been related to two

factors: the presence of Mn2+/Mn4+ or Mn3+/ Mn4+ redox couples and the ability of

active participation of the lattice oxygen in these systems in oxidation process

leading to a Mars van Krevelen type of oxidation mechanism [23, 24]. The

mechanism involves two steps as illustrated in Figure 1.4. Firstly, the lattice oxygen

oxidizes the substrate molecule, followed by a reoxidation of the partially reduced

catalyst by molecular oxygen in order to regenerate the catalyst.

To date, however, the report on liquid phase oxidation via Mars-van

Krevelen-type mechanism is limited, i.e., homogeneous catalysis by

phosphovanadomolybdate [29] and heterogeneous catalysis by OMS-2 catalyst [23,

9

24]. The high selectivity of product makes this mechanism interesting and

worthwhile for intensive study.

Figure 1.4: Mars van Krevelen mechanism.

1.1.3 Modification of OMS-2 Materials

In order to alter their structures and properties and generate better electronic

and catalytic performance, the modification was done by doping cation into OMS-2

materials. The cations doped into OMS-2 materials are listed in Table 1.2. These

cations can substitute potassium and/or manganese ions which exist in the tunnel and

framework structure, respectively [30]. Doping of alkali metals or NH4+ or H+ was

reported to substitute some potassium ions which exist in the tunnel structure of

OMS-2 materials. Transition metal oxides were incorporated in the framework

and/or exist in the tunnel structure. The existence of metal oxides in the framework

indicated that those metal oxides were substituted for manganese. When metals exist

in a tunnel structure, it suggests that the metals have replaced potassium. The

location of doped metal depends on the preparation method [31]. The transition

metal cations are mostly situated in the framework positions of the OMS-2 structure

with a priori incorporation. In a posteriori incorporation, the cations are situated in

either the tunnel positions (if prepared by ion-exchange) or in extraframework

positions (if prepared by homogeneous precipitation).

10

Table 1.2: The cations were doped OMS-2 and their location in OMS-2 material.

Doping cations Location References

H+/NH4+ In tunnel structure [23, 24, 32]

Alkali metals In tunnel structure [32-34]

Transition metals In framework and/or tunnel structure [27, 30, 31, 35-46]

The summary on incorporation of transition metals into OMS-2 materials is

shown in Figure 1.5. Among these transition metals, titanium incorporated OMS-2

has not been reported and therefore is appropriate to be explored.

Have been doped into OMS-2 Not studied

CdAgPdRhRuTcMoNbZr

Cr Cu ZnNiCoFeMnVTi

Have been doped into OMS-2 Not studied

CdAgPdRhRuTcMoNbZr

Cr Cu ZnNiCoFeMnVTi

Figure 1.5: Partial periodic table showing transition metals that have been

incorporated into OMS-2 materials.

The physical and chemical properties of doped OMS-2 are greatly influenced

by the type, amount and location of the doping ions, where the properties of doped

materials are significantly different from those of the undoped ones [12]. In the

tunnel cations position, H+ doped OMS-2 exhibits the surprising activity in oxidation

of alcohols and acid-catalyze condensation of phenylhydroxylamine with aniline to

2-aminodiphenylamine. Among the transition metal doped OMS-2 materials, Fe-

OMS-2 seems to be the best catalyst in some catalytic reactions such as oxidative

dehydrogenation of 1-butene [40], oxidation of toluene [41], decomposition of the

cyanine dye and pinacyanol chloride [44], and oxidative dehydrogenation of ethanol

[46]. However the activity of Fe-OMS-2 is lower than Co-OMS-2 in oxidation of

styrene [27]. It suggests that the activity of metal doped OMS-2 also depends on the

type of substrates involved in the reactions.

11

Titanium oxide attracts much attention in catalysis as well as photocatalysis

and it has been used in the synthesis of many chemical compounds. Titanium

incorporated material shows outstanding catalytic properties, particularly in liquid

phase oxidation process [47-49]. Shell catalyst (Ti(IV)/SiO2) is the basis of the

commercial process for the epoxidation of propene with ethylbenzene

hydroperoxide. Thus, the discovery of titanium silicate-1 (TS-1) by Taramasso et al.

[50] exhibited the remarkable catalytic activity, selective epoxidations with 30%

aqueous hydrogen peroxide under very mild conditions, constituted a milestone in

oxidation catalysis. The discovery of TS-1 led to the study on incorporation of

titanium into porous materials: microporous material such as silicoaluminophosphate

(SAPO-5) and aluminophosphates (AlPO-5, AlPO-11 and AlPO4-36) and

mesoporous materials such as MCM-41 and MCM-48.

The incorporation of titanium into manganese oxide molecular sieve

frameworks is feasible because of similar sizes, charges, and coordination tendencies

of manganese and titanium cations. Ionic radii of octahedral Mn3+, Mn4+, and Ti4+ of

0.65 Å, 0.53 Å and 0.61 Å, respectively [54-55] in crystals are close to one another,

hence Ti4+ can easily substitute either Mn3+ or Mn4+ without causing much structural

disorder and serious charge imbalance. Due to the mixed-valence character of

manganese in OMS-2, this material has distinct advantages over silicate,

aluminosilicate and aluminophosphate molecular sieve materials in catalytic

applications [12, 30]. The incorporation of titanium into OMS-2 is expected to give

excellent performance in oxidation reaction.

The previous sections have demonstrated that OMS-2 and metal doped OMS-

2 materials are potential catalysts in oxidation reactions. The catalytic activity of

metal doped OMS-2 varies depending on the substrate. Further study of the metal

doped OMS-2 is required in order to understand the physicochemical properties-

catalytic activity of the catalysts. Besides that, the effect of titanium incorporated

OMS-2 has not been reported. Therefore, the study on the effect of titanium

incorporated OMS-2 to the physicochemical properties and catalytic activity of

OMS-2 material in oxidation reaction is needed. Further investigation in the

potential application of Ti incorporated OMS-2 in consecutive oxidation and acid

12

reaction should be done. The next section describes how Ti incorporated OMS-2 is

modified to bifunctional oxidative and acidic catalyst.

1.1.4 Design of Sulphated Ti-OMS-2 as Bifunctional Oxidative and Acidic

Catalyst

A bifunctional or multifunctional catalyst is the catalyst which has two or

more active sites. The catalysts have active sites which can catalyze two or more

transformations which are carried out as a “one-pot” process. They offer a number

of advantages to the organic chemist: in particular, they result in a reduced number of

operations, giving significant time-cost benefits, but they also often allow “difficult”

intermediate compounds (i.e., those that are volatile, toxic, or otherwise noxious) to

be prepared and elaborated in situ, thus preventing problems associated with their

isolation and handling [51].

A bifunctional oxidative and acidic catalyst catalyzes for oxidation and acid-

reaction, respectively. The catalyst effectively directs transformation of alkenes to

alcohols. The oxidative sites catalyze the oxidation of alkenes to epoxide followed

by transformation of epoxide to diols in the presence of Brönsted acid site in the

catalyst. At present, 1,2-diols are manufactured industrially by a two-step sequence

consisting of epoxidation of an olefin with a peracid followed by hydrolysis of the

resulting epoxide as shown in Figure 1.6.

Figure 1.6: Transformation of alkenes to diols via two step reaction.

Recently, Prasetyoko et al. [52-54] reported that titanium silicalite (TS-1)

loaded with sulphated zirconia or niobium oxide demonstrated bifunctional oxidative

and acidic properties. However, TS-1 is expensive and difficult to prepare. The

13

purpose of this research is to design a novel bifunctional oxidative and acidic

catalyst. Combining oxidative OMS-2 and acidity, one can come up with the

bifunctional catalyst for consecutive liquid phase oxidation and acid reactions.

Sulphated titanium oxide is a solid superacid which exhibits both Lewis and

Brönsted acidity [55] which are considered as acid sites. The solid acid is used to

overcome the problems of using homogeneous acid.

One approach is to create acidity via incorporation of acidic sites in the

framework of OMS-2. It is expected that bifunctional oxidative and acidic catalyst

can be created by sulphation of TiO2 phase in titanium supported OMS-2 (Ti-OMS-

2) to form SO42--TiO2 superacid active site. Based on this consideration, a catalytic

model of consecutive oxidation and acid catalyst (sulphated Ti-OMS-2) to catalyze

consecutive reactions of alkenes to alcohols e.g. 1-octene to 1,2-octanediol could be

synthesized. MnO6 octahedra as a basic of OMS-2 unit acts as an oxidative site for

epoxidation of 1-octene to 1,2 epoxyoctane and SO42--TiO2 superacid acts as an

acidic site for transformation of 1,2 epoxyoctane to 1,2 octanediol. Hence the use of

OMS-2 materials which are relatively cheap and easily prepared and use a mild

oxidant for oxidation process and sulphated TiO2 environmentally friendly as acid

sites is expected to be the best solutions to overcome the related problems.

1.2 Research Questions and Scope of Research

Based on the above descriptions, one considers that OMS-2 is the potential

heterogeneous catalysts for liquid phase oxidation. Although modification of OMS-2

by doping of transition metal oxides have been reported but Ti incorporated OMS-2

has not been reported yet [30-46]. The effect of the location, amount and synthesis

method of titanium incorporated OMS-2 to the catalytic properties of OMS-2 in

some oxidation reactions have not been studied yet. The relationship between

physicochemical properties and catalytic activity of titanium and other metals

incorporated system are not well understood. In addition, design of bifunctional

oxidative and acidic catalyst in order to form the more effective and efficient catalyst

14

for consecutive oxidation and acid reactions is a challenge that has less studied.

Modification of OMS-2 by enhancement of the oxidative ability and creation of the

acid site may together be beneficial and advantageous to create the bifunctional

catalyst for synthesis of diols from alkenes.

Figure 1.7 shows the research approach and questions of the research. The

research includes the study on effect of synthesis method and some modifications to

physicochemical properties of OMS-2 and their correlation to catalytic activity of the

catalysts. Generally, there were two categories of modifications of OMS-2; firstly,

metals substituted and H-exchanged, aimed to improve the catalytic oxidation of

OMS-2 catalyst. The catalysts were characterized by several characterization

methods to find out their physicochemical properties. Thus, those were correlated to

the catalytic activity of the catalysts in oxidation of cyclohexane. However, this

study emphasized on titanium incorporated OMS-2. The effect of synthesis method,

amount and location of the titanium substituted to the physicochemical properties of

OMS-2 were evaluated. Characterizations were done by several methods such as

structural and acidity analysis, surface area, hydrophobicity-hydrophylicity, etc.

Thus, their physicochemical properties were correlated to catalytic activity of the

catalyst in several oxidation reactions such as cyclohexane, cyclohexene and styrene.

The second modification was sulphation of titanium supported OMS-2 aimed to

create acid sites on the oxidative catalyst. The catalysts were characterized and

tested in consecutive oxidation and acid reactions for direct synthesis of diols from

alkene. Briefly, the research attempted to answer some questions as depicted in

Figure 1.7.

1.3 Research Objectives

The research proposed is a fundamental study of heterogeneous catalytic

system for both oxidation process and consecutive reaction of alkenes to alcohols

under mild conditions. Since it is a one step, inexpensive and easy preparation of the

15

Figure 1.7: The schematic of the research approach and research questions.

Research Questions

Synthesis � OMS-2 synthesized in different

methods � Synthesis of metals substituted

OMS-2 (M = Ti, Fe, Cu, Co) � H-exchanged OMS-2 � Sulfation of Ti-OMS-2

1. Which method gives the best performance of OMS-2 in oxidation of benzyl alcohol.

2. What are the effects of metals substituted and H-exchanged to the physicochemical properties of OMS-2 and its correlation to catalytic activity of the catalyst in oxidation reaction?

3. How are the catalytic activities of Ti-OMS-2 compared to the other metals incorporated OMS-2?

4. What are the effects of the synthesis method, amount and location of titanium sites to physicochemical properties of Ti-OMS-2 and its correlation to catalytic activity in oxidation reaction?

5. How is catalytic activity of Ti sites in different substrates in oxidation reaction?

6. Is sulfation of Ti-OMS-2 catalyst successfully designed as a bifunctional oxidative and acidic catalyst for synthesis of diols from alkene?

Characterization � Structural analysis � Acidity analysis � Surface area � Hydrophobicity-

hydrophilicity

Catalytic activity � Oxidation reactions � Consecutive

oxidation and acid reactions

16

catalyst using mild oxidant as oxidizing agent, these systems are more economical

and environmentally friendly (see Figure 1.8).

In light of the issues described previously, the research was conducted with

the following objectives:

1. To synthesize manganese oxide octahedral molecular sieve (OMS-2),

titanium supported OMS-2 (Ti-OMS-2), metal supported OMS-2 (M-

OMS-2) and H doped metal supported OMS-2 (H-M-OMS-2).

2. To modify the surface of Ti-OMS-2 by sulphation as a bifunctional

catalyst.

3. To study the physicochemical properties-catalytic activity relationship in

model reactions.

17

Figure 1.8: The significant of the use Ti-OMS-2 in heterogeneous oxidation and acid

reactions.

Multidisciplinary Science

Catalysis

� Success of the industry in 20th century � Greener industry in 21th century � The heart of quality of life � A healthy economy growth

Oxidation reaction Acid-catalyze reaction

� OMS-2 as a promising heterogeneous catalyst (active with mild oxidant, inexpensive and easy preparation)

� TS-1 as a milestone in oxidation catalysis

Sulfated metal oxide as a strong solid acid catalyst which more environmentally friendly

A new heterogeneous catalyst for oxidation reaction under mild condition

Ti-OMS-2

Significant

Sulfated Ti-OMS-2

Catalyst Design

Bifunctional oxidative and acidic catalyst for consecutive reaction of alkene to diols (one pot reaction)

More economic and environmentally friendly catalysts

Importance

Catalyst Design

Biggest problem

areas