An efficient Au/ZnO catalyst for the photocatalytic conversion of methane to formaldehyde

The photocatalytic oxidation of methane to value-added chemical products under mild conditions is crucial for resource utilization and environmental protection. However, inefficient generation of reactive oxygen species partially limits methane activation. To tackle this issue, we have developed highly dispersed Au-modified ZnO nanosheets through photo-deposition method for the photocatalytic oxidation of methane to formaldehyde. The optimized Au-0.1/ZnO catalyst (0.1 wt% Au on ZnO) achieves a HCHO yield of 19.14 mu mol h(-1) with a selectivity of 87.94 %. Electron paramagnetic resonance, Raman, X-ray photoelectron spectroscopy and density functional theory show that Au enhances the concentration of oxygen vacancies (OVs) in ZnO. This enhancement is attributed to a strong interaction between Au and ZnO, which facilitates the transfer of electrons from the ZnO surface to Au. Under irradiation, Au and OVs function as hole and electron acceptors, respectively. This interaction promotes carrier separation, reduces charge recombination, enhances oxygen adsorption, and effectively generates reactive oxygen species, such as <middle dot>OH. Subsequently, CH4 is oxidized to <middle dot>CH3 by holes from Au. Concurrently, O-2 is reduced by electron from OVs, following the pathways O-2 -> OOH -> H2O2 -> <middle dot>OH. The rapid oxidation of CH3OH by <middle dot>CH3 and <middle dot>OH results in the formation of HCHO.