Fine Control of the Pore-Opening Size of Zeolite ZSM-5 by Chemical Vapor Deposition of Silicon Methoxide

Article abstract of DOI:10.1021/j100281a033

The pore-opening size of ZSM-5 was finely controlled by the chemical vapor deposition (CVD) of silicon methoxide.The silicon compound vapor was deposited, and the deposited material was calcined by oxygen, finally forming a silica-coated zeolite (SiHZSM-5).This was characterized by temperature-programmed desorption of ammonia and adsorption experiments using various molecules.It was found that the silica was deposited only on the external surface and narrowed the pore-opening size effectively with the internal structure unaltered.The fine control of the pore-opening size was tested, exemplified by the conversion of methanol.Hydrocarbon product distribution shifted to smaller molecules over the SiHZSM-5: the formation of smaller olefins such as ethylene and propylene increased in place of the complementary decrease of large aromatics.Enhancement of the preoduct shape selectivity was remarkable in xylene isomers and larger aromatics, which indicated the fine controls of the pore-opening size according to the deposition extent.Structures of the CVD zeolite and the enhanced shape selectivity in the methanol conversion were discussed.