Adedigba, A-LA; (2016) Synthesis and catalytic performance of hierarchically structured zeolitic materials. Doctoral thesis , UCL (University College London).

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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 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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