Synthesis Of Hierarchical Mesoporous Silica Templated With Ionic Liquids And Organosilane

Microporous silica materials, represented by ZSM-5 and TS-1, have been studied extensively in the fields of adsorption, separation, catalysis and so on. Unfortunately, the narrow channel makes them inactive in the bulky molecules reactions. Mesoporous silica has capacious framework pores (>2 nm) and large surface area that can exhibit high activity in some big molecule reactions. However, the relative lower hydrothermal stability of these mesoporous materials, arising from the amorphous nature of their pore walls prevents them from comprehensive applications in the industrial process. The purpose of this paper is to synthesize novel micro/mesoporous materials, in order to overcome the shortcomings of existing zeolite molecular sieves.The paper has the following main contents.Spherical mesoporous silica has been synthesized using a mixture of 1-methyl-3-octylimidazolium chloride and cetyltrimethylammonium bromide as the structure-directing agent. The characterization results show that the spherical silica possesses worm-like mesopores and larger mesopores, with the sizes of around 6-50nm. It is very interesting to observe that the spherical mesoporous spheres were converted to hollow ones after refluxing in boiling water. The treatment resulted in the generation of the hollow interior by dissolving the silica core. Meanwhile, the silica shell was well retained, which was further confirmed by SEM and TEM images.Hierarchical TS-1 has been synthesized in the presence of cationic organosilane surfactant using TEOS as silica source, TPAOH as template and TBOT as titanium source. The characterization results show that the hierarchical TS-1 aggregates consist of small primary units with sizes of 20-30 nm. The BET surface area increases from 420 m2g-1 to 513 m2g-1 compared to conventional TS-1 zeolite. The sample is shown to be more active in epoxidation of cyclohexene than conventional TS-1.The novel nano-ZSM-5 has been synthesized by sol-gel method using TEOS as silica source, TPAOH as template agent and aluminium isopropoxide as aluminium source. The particle size of this sample is about 150 nm, without agglomeration. Hierarchical ZSM-5 has been synthesized also in the presence of cationic organosilane surfactant using water glass as silica source, NBA as template, and aluminium sulfate as aluminium source. The results show that the organosilane does not significantly affect the textural properties of ZSM-5. The nanocrystals which consists of hierarchical ZSM-5 decreased greatly, therefore generated much more mesopores between these nanocrystals. The BET surface area also increases from 397 m2g to 542 m2g compared with conventional ZSM-5. The mesoporous ZSM-5 exhibited much higher catalytic activity in the methylation of toluene with methanol compared with conventional ZSM-5.