Synthesis of hierarchical Sn-Beta zeolite and its catalytic performance in glucose conversion

摘要

Hierarchical Beta zeolites are successfully synthesized with hydrothermal method in the presence of polydiallyldimethylammonium chloride (PDADMA). Followed a dealumination process, hierarchical Sn-Beta are post-synthesized by the solid-gas reaction of dealuminated Beta zeolite with SnCl4 vapor. All samples are charcterized with XRD, N2 sorption, SEM and TEM. SEM images show that both Beta zeolite and Sn-Beta zeolite exhibit rough spherical-like morphology of about 500-900 nm in diameters, N2 sorptions show the pore size distributions in micropore and mesopore ranges, indicating the formation of mesoporous Beta zeolites. It is proofed that Sn species are doped into the framework in a tetrahedral environment during solid-gas reaction and the introduction of Sn species has negligible impact on the structure of Beta zeolites. Furthermore, the dehydration of glucose into HMF which needs both Bro?nsted and Lewis acid is selected to evaluate the catalytic performance of hierarchical Sn-Beta. It displays good catalytic activity, the conversion of glucose (99 %) and selectivity to HMF (42 %) are higher than those of the conventional Beta (96 % and 32 %, respectively). This is attributed to the intra-crystalline mesoporous structure and efficient diffusion of reactant/product molecules. Moreover, the catalyst exhibits steady catalytic performance after the fifth repeated run.