Understanding the Catalytic Sites in Porous Hexagonal Boron Nitride for the Epoxidation of Styrene

摘要

Porous hexagonal boron nitride (ph-BN) nano-sheets were synthesized via the combustion of boric acid and melamine by a pyrolysis method. The as-obtained ph-BN showed a high catalytic activity for the epoxidation of styrene using tert-butyl hydroperoxide as an oxidant. Both experimental and theoretical study demonstrated that the activity originated from the oxygen-containing functional groups at the edges of ph-BN. To further understand the mechanism for this catalytic behavior, in situ Fourier transform infrared spectroscopy in a diffusion reflectance model has been used to monitor the evolution of surface functional groups of ph-BN treated at different temperatures (50-800 degrees C). In this way, the active functional groups on the ph-BN have been identified. It was revealed that B-OH groups dehydrate to form BO-B edges and are further oxidized to B-O-O-B type edges. B-OH is the main active site responsible for the epoxidation of styrene, while B-O-O-B edges have a similar activity. Finally, a plausible reaction pathway was proposed for the epoxidation of styrene on this metal-free catalyst based on the density functional theory calculation. A clear understanding of the catalytic sites for this metal-free catalyst and the functional group tuning strategy in this work may expand the BN-based material for various catalytic applications.

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