Synthesis and catalytic properties of ZSM-5 zeolite with hierarchical pores prepared in the presence of n-hexyltrimethylammonium bromide

Abstract

ZSM-5 samples with hierarchical pores (macropores, mesopores and micropores) were synthesized in the presence of n-hexyltrimethylammonium bromide (HTAB) and tetrapropylammonium hydroxide (TPAOH). The effect of synthesis conditions including the Si/Al ratio, crystallization temperature and time, and the amount of HTAB added to the synthesis system on the final products was examined. The catalytic properties of the hierarchical zeolite were investigated in reactions of Claisen–Schmidt condensation of benzaldehyde and acetophenone, self-condensation of cyclohexanone and methanol conversion. The hierarchical zeolite exhibits superior catalytic performance in Claisen–Schmidt condensation of benzaldehyde and acetophenone and self-condensation of cyclohexanone and has a remarkably high selectivity for dimethyl ether in the methanol conversion reaction at relatively low temperatures, which was attributed to the fast mass transport in the three-dimensional hierarchical pore network. A cooperative assembly mechanism accounting for the formation of the hierarchical zeolite was proposed based on experimental results.