Photocatalytic property of WO3 modified with noble metal co-catalysts towards selective hydroxylation of benzene to phenol under visible light irradiation

Direct synthesis of phenol from benzene in the presence of water and oxygen were conducted under visible-light irradiation. Effects of several noble metal co-catalyst on the selective hydroxylation of benzene over WO3 photocatalysts have been extensively studied. The photocatalytic activities of WO3 for phenol formation strongly depend on co-catalyst such as Pt, Au, Pd metal species, i.e., phenol formation was as follows: Pt-WO3 > Au-WO3 > Pd-WO3. Furthermore, the WO3 photocatalyst deposited bimetal co-catalysts such as Pd/Pt, Pd/Au and Pt/Au were also investigated. The Pd/Pt-WO3 photocatalyst was found to show the highest photocatalytic activity for phenol formation due to an effective oxygen reduction reaction (ORR) for bimetallic Pd/Pt cocatalyst. From the experimental and theoretical studies, phenol was confirmed to form by the insertion of OH derived from H2O into benzene, and simultaneous cleavage of benzylic carbon-hydrogen bond (Csp2-H) by an assist of co-catalyst surface through the push-pull process.