Synthesis And Catalytic Properties Of Micro/Mesoporous Zeolite Y Based On Imidazole-Based Ionic Liquid

Microporous zeolite Y is account for massive use in industry thanks to their advantages of strong acid strength, good shape selectivity characters and excellent thermal/hydrothermal stability. However, the molecular dimension of the micropore is only about 7.4 A. Reactants and products with sizes beyond 7.4 A will slow transport to/from the active sites, leading to an intolerably slow intracrystalline diffusion rate. This has been a major drawback for the industrial applications of zeolites Y. Mesoporous materials have gained increasing interest, because the large pore diameter allows grafting of bulky organic molecules. Thus, it is possible to integrate hierarchically micro-mesoporous aluminosilicate materials to tackle the conflict between pore accessibility and catalytic activity. Hierarchical zeolite Y with the combined advantages of both mesoporous properties and the microporous crystalline structure of zeolites exhibited high catalytic activity in the reaction involving large molecular, as compared with the conventional zeolite with sole presence of micropores.1,2-Diphenylethane (PXE) is an appropriate solvent for the pressure-sensitive record materials, and can be obtained by the alkylation of o-xylene with styrene. The micro-mesoporous zeolites NaY were synthesized with MTPI as the template. Moreover, the H-form samples of zeolite Y were obtained by repeated procedure of ion exchange. The catalytic properties of the catalysts were assessed in the alkylation of o-xylene with styrene.The mesoporous zeolite NaY was hydrothermally synthesized by addition of ionic liquid (MTPI) into the conventional synthesis compositions of zeolite NaY. The influence of the molar ratio of MTPI/Na20 (n) and crystallization temperature (x) during synthesis were investigated. The result shows that the sample NaY-0.15MTPI at the hydrothermal temperature of 100℃ exhibits a BET surface area of 690 m2·g-1, in the case,76 m2·g-1 is from the external surface and the mesopore volume is increased to 0.11 cm3·g-1. It is noteworthy that classical zeolite HY has poor catalytic performance. While a significant increase of yields of PXE are achieved with all the hierarchical zeolites HY-nMTPI. Especially, the sample HY-0.15 MTPI shows the best catalytic performance in terms of yield and selectivity, which can be attributed to its maximum mesoporous volume, abundant acid amount and structural properties which are favorable for fast diffusion of products.Hierarchical zeolites NaY are successfully synthesized by different methods using IL as a mesopore director. And the influence of ultrasonic/microwave synergistic synthesis (UMSS) and conventional hydrothermal synthesis to the structure of the final materials has been investigated. The results show that the UMSS method not only makes productive process inexpensive, facile, scalable, and controllable, but also produces the zeolites with large surface area, bulky pore volume as well as excellent crystallinity with hydrothermal time of 6 h. Besides, the sample NaY(UMSS) has well-dispersed cauliflower-like morphology with short diffusion path length, thus reactants diffuse easily into the pores and correspondingly the products also diffuse out freely. Therefore, HY(UMSS) exhibits a high product yield and long catalytic life in the alkylation of o-xylene with styrene.A series of hierarchical zeolites NaY were synthesized by changing the molar ratio of SiO2/Al2O3 of the solution during synthesis. The final products were denoted as z NaY (z= 11,10.5,9.5,8.5), wherein z represents the molar ratio of SiO2/Al2O3. The results clearly show that with the increase of the molar ratio of SiO2/Al2O3, the crystal crystallinity, BET surface areas and mesopore volume of samples z NaY are first increased then decreased. Moreover, the hierarchical zeolites z HY synthesized in an Al-rich system (z≤10.5) show improved catalytic activities. Especially, the hierarchical sample HY prepared at SiO2/Al2O3= 9.5 shows the best catalytic performance in terms of yield and selectivity, which can be attributed to its large mesoporous volume and abundant acid amount.In conclusion, the micro-mesoporous zeolite Y using ionic liquid as mesoporous structure-directing agent possess high surface area, large mesopore volume and abundant acid amount. And these hierarchical materials with advanced properties would play significant roles in the alkylation of o-xylene with styrene.