Insight into the Effective Aerobic Oxidative Cross-Esterification of Alcohols over Au/Porous Boron Nitride Catalyst

Boron nitride (BN) has attracted great attention with an unexpected ability in aerobic catalysis. Still, its related probe reactions are relatively rare, and the effect of the BN-supported metal catalyst on O₂ activation is still ambiguous, and opinions are varied. In this work, the porous BN (pBN)-supported Au catalyst with a porous structure and exposed edges exhibits high activity in the oxidative cross-esterification reactions between the aromatic and C₁-C₃ aliphatic alcohols at ambient temperature. The turnover frequency value for methyl benzoate is 118 h^-1 at 30 °C, and the calculated apparent activation energy (Ea, 58 kJ/mol) is comparable to that of AuPd/TiO₂, Ru/Al₂O₃, and PdBiTe catalysts. Combined with temperature-programmed  desorption (TPD) results, the loading of Au enhances the desorption of O₂ and the interaction with alcohols; thus, a synergistic effect between the O-rich pBN and Au is considered. The free-radical scavenger can dramatically suppress the conversion (∼6%), suggesting that the reaction proceeds via the O₂* radicals. According to the vibration of ν_O-O, δ_OO-H, and ν_B-O-O-B detected by attenuated total reflectance-infrared spectroscopy (ATR-IR), we are prone to consider the oxygen activation route by the edge B atoms. Then, a possible L-H reaction mechanism was proposed: benzyl alcohol and O₂ adsorb on the Au/pBN initially, then O₂ is converted to O₂*, and the α-H elimination proceeds; as the semi-acetal formed, another α-H elimination proceeds and methyl benzoate is finally formed.