Surface silanol sites in mesoporous MFI zeolites for catalytic Beckmann rearrangement

Abstract

Silanol groups were generated in siliceous MFI zeolite nanosheets, via alkali-free synthesis routes, for catalytic application for gas-phase Beckmann rearrangement. The catalytic conversion by the zeolite nanosheets was investigated at 310 or 350 °C with cyclohexanone oxime, 4-phenylcyclohexanone oxime and cyclododecanone oxime. Here, cyclohexanone oxime was chosen as a small reactant that should be able to diffuse into the zeolite micropores, while the others were too bulky to diffuse. The catalytic conversion was analyzed in reference to a previous method used to generate hydrogen-bonded silanol nests in bulk-crystalline MFI zeolites using NH₃/NH₄⁺. The result of the analysis indicated that the silanol nest was necessary for the catalytic conversion of cyclohexanone oxime and 4-phenylcyclohexanone oxime, but isolated silanols on the external surface were sufficient for the reaction of cyclododecanone oxime.