Catalytic methane oxidation to methanol using supported Cu-introduced polyoxometalate cesium salt catalysts

Abstract Selective methane (CH4) oxidation to methanol (CH3OH) is a highly desirable reaction; however, it remains challenging due to the high stability of CH4 and the facile over-oxidation of the products. Recently, Cu-based catalysts have been reported as promising candidates for continuous CH3OH production from CH4. Here, we demonstrated that supported Cu-introduced polyoxometalate (POM) cesium salts catalytically produced CH3OH at 450 °C. Notably, monocopper-introduced POM cesium salts (Cs-Cu1/SiO2) selectively produced CH3OH (>75%), maintaining a stable CH3OH yield over a 24 h time on stream. In contrast, CH3OH was prone to over-oxidation into carbon monoxide (CO) and carbon dioxide (CO2) over Cu(OAc)2/SiO2 or monocopper-introduced POM tetra-n-butylammonium salts (TBA-Cu1/SiO2), due to the aggregation of CuO species. Cu K-edge XANES and Raman spectroscopy revealed that the supported POM cesium salts functioned as molecular templates and potentially prevented the aggregation of Cu active sites.