Understanding the Catalytic Sites in Porous Hexagonal Boron Nitride for the Epoxidation of Styrene
Porous hexagonal boron nitride (ph-BN) nanosheets 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 °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 B–O–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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