Synthesis and Catalytic Performance of Hierarchically Structured Zeolitic Materials Abdul-Lateef ...

226 Pages·2016·12 MB·English

Synthesis and Catalytic Performance of
Hierarchically Structured Zeolitic
Materials

Abdul-Lateef Ajibade Adedigba

University College London

Thesis submitted in partial fulfilment of the
requirements for the degree of doctor of Philosophy
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Declaration
I, Adedigba Abdul-Lateef Ajibade, confirm that the work presented in this thesis is
my own. Where information has been derived from other sources, I confirm that this
has been indicated in the thesis.

Signed…………………………

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Abstract
The work presented in this dissertation involves the investigation of the synthesis
methodology of hierarchically structured zeolite and their catalytic performances. To
create these materials, an inert templating agent, chitosan, as macro-template was
used along with microporous templating agent to produce titanosilicate,
aluminosilicate and titano-aluminosilicate systems with MFI structure.
Firstly, synthesis of the titanosilicate (TS-1) system was carried out. It was found
that, while the use of chitosan did not affect production of crystalline, phase pure
TS-1, the preparation of precursors indeed is an important factor in the insertion of
titanium in the silicalite structure. A range of characterisation methods were used to
establish the nature of titanium species in the catalyst and also the nature of pore
structures present in the system. The catalysts developed here were evaluated for
liquid phase epoxidation of cyclohexene and styrene with their activities and
selectivity correlated with the amount of chitosan included in the synthesis
precursors.
Secondly, the chitosan was transformed into a rigid three dimensional structure
(scaffold) and used as macro-template to form the alumino-silicate (ZSM-5) zeolite.
Parameters such as the amount of zeolite precursor to chitosan scaffold and the ratio
of silicon to aluminium in the starting precursor were found to influence the acidity,
pore distribution and the crystal morphology. The selectivity and coke formation of
these zeolites were evaluated for the methanol to hydrocarbon reaction.
Finally, a zeolite with both redox and acid sites was synthesised in the presence of
chitosan. This catalyst was investigated for direct conversion of cyclohexanone to
caprolactam in the liquid phase. The influence of the amount of chitosan in the
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synthesis, reaction conditions and solvent medium on activity and selectivity was
studied.
In summary, the project successfully investigated the use of chitosan in the
production of hierarchical MFI type zeolite and evaluated the performance for a
range of catalytic reactions
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Table of Contents
Declaration ................................................................................................................... 2
Abstract ........................................................................................................................ 3
Table of Contents ......................................................................................................... 5
List of Figures ............................................................................................................ 12
List of tables ............................................................................................................... 20
List of schemes ........................................................................................................... 22
Acknowledgements .................................................................................................... 23
Chapter 1: Introduction .......................................................................................... 24
1.1 Introduction to Catalysis ............................................................................. 24
1.2 Types of Catalysis ....................................................................................... 25
1.2.1 Homogeneous catalysis .................................................................... 25
1.2.2 Heterogeneous catalysis ................................................................... 26
1.3 Zeolites as heterogeneous catalysts ............................................................. 26
1.4 Structure and topology of zeolites ............................................................... 28
1.5 Advantages of zeolites ................................................................................. 30
1.5.1 Selectivity in zeolite catalysis .......................................................... 30
1.5.2 Acidity in zeolites ............................................................................. 31
1.5.3 Redox functionality in zeolites ......................................................... 33
1.6 Zeolite type materials (zeotype) .................................................................. 35
1.7 Factors limiting the applications of zeolites and zeotype materials ............ 37
1.8 Solutions to the factors limiting the applications of zeolites ....................... 38
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1.9 Hierarchical zeolites .................................................................................... 39
1.10 Post synthesis creation of extra porosity in zeolites ................................ 40
1.10.1 Dealumination .................................................................................. 40
1.10.2 Desilication ....................................................................................... 42
1.11 One-Pot secondary templating synthesis of hierarchical zeolites ............ 42
1.11.1 Soft templating ................................................................................. 43
1.11.2 Hard templating ................................................................................ 43
1.12 Chitosan ................................................................................................... 44
1.12.1 Chitosan in heterogeneous catalysis ................................................. 45
1.12.2 Chitosan for medical applications .................................................... 45
1.12.3 Chitosan for water treatment ............................................................ 47
1.12.4 Chitosan as a source of carbon ......................................................... 47
1.12.5 Chitosan as an inert template for hierarchical zeolites ..................... 47
1.13 Objective and scope ................................................................................. 48
References .................................................................................................................. 50
Chapter 2: Experimental techniques and methodologies ....................................... 55
2.1 Zeolite synthesis techniques ........................................................................ 55
2.1.1 Hydrothermal synthesis technique ................................................... 56
2.1.2 Steam assisted crystallization (SAC) ............................................... 57
2.1.3 Vapour phase crystallization (VPC) ................................................. 58
2.1.4 Hybrid method of crystallization ...................................................... 59
2.2 Advantages of SAC synthesis techniques ................................................... 60
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2.3 Characterization techniques......................................................................... 60
2.3.1 Phase identification by X-Ray diffraction technique ....................... 61
2.3.2 Phase purity ...................................................................................... 62
2.3.3 Sample preparation and procedure for X-ray diffraction
measurement .................................................................................................... 62
2.4 Textural properties and pore characterization ............................................. 63
2.4.1 Sample preparation for BET surface area determination ................. 65
2.5 Acid characterization of zeolite samples - FTIR approach ......................... 66
2.5.1 Sample preparation for FTIR measurement ..................................... 67
2.6 Morphological characterization - Electron microscopy .............................. 68
2.6.1 Working principle of the SEM ......................................................... 68
2.6.2 Sample preparation for SEM analysis .............................................. 69
2.7 Location & coordination state of T-atoms in zeolite frameworks - Raman
spectroscopy technique ......................................................................................... 70
2.7.1 Sample preparation for Raman analysis ........................................... 71
2.8 X-ray absorption spectroscopy (XAS) ........................................................ 71
2.8.1 Sample preparation and procedure for XAS measurements ............ 74
2.9 Thermogravimetric analyzer ....................................................................... 74
2.9.1 Sample preparation for TGA analysis .............................................. 76
2.10 Other techniques employed ..................................................................... 76
2.11 Catalytic reactions and reactor setups ...................................................... 77
2.11.1 Epoxidation reactor setup ................................................................. 77
2.11.2 Liquid phase ammoximation of cyclohexanone to caprolactam ...... 78
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2.12 Gas phase reactor ..................................................................................... 78
2.13 Product analysis by gas chromatography (GC) ....................................... 80
2.14 Product analysis method .......................................................................... 80
2.15 Calibration ............................................................................................... 82
Reference.................................................................................................................... 85
Chapter 3: Effect of structure and hierarchical pores on the catalytic properties of
TS-1……….. .............................................................................................................. 87
3.1 Introduction ................................................................................................. 88
3.2 Experimental ............................................................................................... 91
3.2.1 Materials ........................................................................................... 91
3.2.2 Synthesis technique .......................................................................... 91
3.2.3 Characterization ................................................................................ 93
3.2.4 Catalytic evaluation .......................................................................... 94
3.3 Results and discussions ............................................................................... 95
3.3.1 Phase and phase purity by PXRD ..................................................... 95
3.3.2 Morphological characterization using SEM ..................................... 95
3.3.3 FTIR, Raman and UV-Vis investigation of the coordination state of
titanium.. .......................................................................................................... 98
3.3.4 X-ray absorption spectroscopy measurement ................................. 102
3.3.5 Pore characteristics ......................................................................... 108
3.4 Catalytic evaluation of catalysts ................................................................ 109
3.4.1 Epoxidation of cyclohexene ........................................................... 109
3.4.2 Optimization of the reaction conditions ......................................... 112
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3.4.3 Styrene epoxidation ........................................................................ 114
3.5 Conclusions ............................................................................................... 116
References ................................................................................................................ 117
Chapter 4: Chitosan scaffold templated ZSM-5 and application in methanol to
hydrocarbon reaction ................................................................................................ 120
4.1 Introduction ............................................................................................... 121
4.2 Methanol to hydrocarbon reaction steps.................................................... 125
4.3 Experimental techniques ........................................................................... 126
4.3.1 Scaffold preparation ....................................................................... 126
4.3.2 Zeolite gel preparation .................................................................... 127
4.3.3 Scaffold filling and crystallization ................................................. 128
4.3.4 Characterization .............................................................................. 129
4.3.5 Catalytic reactions .......................................................................... 130
4.4 Results and discussions ............................................................................. 131
4.4.1 Morphology of scaffolds ................................................................ 131
4.4.2 Post synthesis observation .............................................................. 133
4.4.3 Phase identification ........................................................................ 134
4.4.4 FTIR characterization ..................................................................... 137
4.4.5 Morphological investigation by SEM ............................................ 143
4.4.6 Textural characterization ................................................................ 146
4.4.7 Location of T-atoms ....................................................................... 150
4.4.8 Catalytic evaluations ...................................................................... 152
4.4.9 Coke analysis .................................................................................. 160
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4.5 Discussion and conclusions ....................................................................... 165
References ................................................................................................................ 167
Chapter 5: Bifunctional zeolite and application to liquid phase conversion of
cyclohexanone to caprolactam ................................................................................. 171
5.1 Introduction to dual functional catalysts ................................................... 172
5.2 Experimental procedure ............................................................................ 176
5.2.1 Synthesis procedure ........................................................................ 176
5.2.2 Sample notations ............................................................................ 178
5.2.3 Characterization .............................................................................. 178
5.3 Phase identification and phase purity determination by XRD .................. 178
5.4 Coordination state of titanium, silicon and aluminium ............................. 180
5.5 NMR characterisation ................................................................................ 184
5.6 Acidity of the samples by in situ FTIR ..................................................... 186
5.7 Investigation of the morphology by SEM ................................................. 189
5.8 Textural properties .................................................................................... 189
5.9 Catalytic evaluation ................................................................................... 190
5.9.1 Cyclohexanone ammoximation and Beckmann rearrangement ..... 191
5.9.2 Gas-phase Beckmann rearrangement ............................................. 196
5.9.3 Methanol to hydrocarbon conversion ............................................. 198
5.10 Post reaction catalyst analysis................................................................ 199
5.10.1 Coke analysis .................................................................................. 199
5.10.2 Nature of coke ................................................................................ 202
5.10.3 Catalyst regeneration ...................................................................... 204
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