Synthesis and catalytic properties of ionic liquid-templated zeolites.

Zeolites have been gained continuous attention from both academic and industrial perspectives due to their outstanding properties, such as tunable acidity, well-defined pore system, large surface area, high thermal stability, excellent shape selectivity and insertion of metal active species. In the zeolite synthesis area, applying new structure-directing agents (SDAs) and exploring the crystallization mechanism have always been frontier topics. This thesis aimed to explore the structure-directing effect of ionic liquids (ILs) as SDAs in zeolite synthesis and the elusive role of tetraethyl orthosilicate (TEOS) hydrolysis in ionic-liquid-templated zeolite synthesis in determining the ultimate zeolite type. Also, the catalytic performances of the ionic liquid-templated zeolites in model reactions were studied. Experiments were designed based on the preliminary results to explore the relationship between imidazolium and the resulting zeolite structures in 10-membered ring zeolite synthesis. The results demonstrated that the structure types of the zeolites obtained by imidazolium- directed synthesis are independent of the silica sources with the following trend: EMIM and BMIM favor the formation of the TON and MFI structures, respectively. However, using TEOS as a silica source does not follow the abovementioned trend. Herein, experiments elucidating the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis were carried out. The results showed that the dissolved silica concentration in the synthesis solution. Specifically, in [BMIM]Br-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. Two model reactions, propene dimerization and toluene methylation reaction were conducted to explore the shape-selective capability of the ionic liquid-templated ZSM-22 and ZSM-5 zeolites. In propene dimerization reaction, the confinement effect accounted for the dimer selectivity difference: at the low propene conversion (< 5%), the TON-type zeolites (Si/Al ratio range of 30 - 120) obtained a dimer selectivity over 70% whereas MFI-type zeolites (Si/Al ratio range of 30 - 120) reached less than 42%; in toluene methylation reaction, the ZSM-22 gave a significantly higher para-xylene (p-xylene) selectivity than the ZSM-5 zeolites and that the ZSM-22 with smaller particle sizes exhibited the highest p-xylene selectivity, up to 92%. The confinement effect due to different channel systems (1D channel in TON vs 3D channels in MFI) was key for determining the different catalytic performances between TON- and MFI- type zeolites. This work filled the gap in the literature that the role of TEOS hydrolysis in ionic-liquid- templated zeolite synthesis is vague and would contribute to the understanding of the zeolite crystallization mechanism. Also, the studies on the catalytic applications of ionic liquid- templated zeolites were rare, thus the results of model reactions using ionic liquid-templated zeolites in this thesis would contributed to the application of ionic liquid-templated zeolite for industrial processes