Metal oxide-containing SBA-15-supported gold catalysts for base-free aerobic homocoupling of phenylboronic acid in water

Abstract

Metal oxide-containing SBA-15-supported gold catalysts were prepared by depositing gold on the SBA-15 pre-loaded CeO2, TiO2 or ZrO2 and applied to the base-free aerobic homocoupling of phenylboronic acid in water. The results of catalytic tests showed that the small-sized metallic gold nanoparticles (size 1.3–2.3nm) deposited on the metal oxides were all active for the reaction and possessed much greater activity than cationic gold species. The conversions and the product selectivities for the catalysts are high (>72% and >94% respectively) and the catalysts were reusable under mild conditions. X-ray absorption investigation indicated that the gold nanoparticles in the catalysts retained a metallic nature under reaction conditions. Furthermore, results indicated that the nucleophilic tetravalent boron was formed in neutral reaction conditions and that both oxygen and water were involved in the reaction. Based on these experiments, a reaction mechanism was proposed for the base-free aerobic homocoupling reaction by the metal oxide-containing SBA-15-supported gold catalysts.