LAUSR

Abstract A series of tungsten-tin bimetallic MFI type zeolites (WSn-MFI) with different Sn and W contents were hydrothermally synthesized using tetrapropyl ammonium hydroxide (TPAOH) as a template and polypyrrolidone as a co-surfactant. Tetraethylorthosilicate (TEOS), ammonium tungstate hydrate and tin (IV) chloride pentahydrate were used as the Si, W and Sn sources, respectively. The resultant samples were characterized by various techniques, and were evaluated as catalysts for the epoxidation of cyclohexene with hydrogen peroxide. The results reveal that all the W–Sn bimetallic zeolites have the typical MFI structure, and their relative crystallinities and morphologies change somewhat with the variety of W and Sn contents. Both the isolated framework SnO4 species and the extra-framework SnO2 species could be detected in all WSn-MFI samples, while only trace amount of extra-framework W species are present inside the channels/cages of the bimetallic zeolites. Compared with the monometallic zeolites of W-MFI and Sn-MFI, the bimetallic WSn-MFI zeolites exhibit much higher catalytic activity for the epoxidation of cyclohexene. Of these, the sample named WSn-MFI-a could efficiently convert cyclohexene to the corresponding epoxide with a high yield of 79% under an optimized reaction condition. A synergistic effect between the W and Sn species should play critical role in improving the catalytic activity and the epoxide selectivity of the bimetallic zeolite catalysts.