Aerobic oxidation of methane to formaldehyde mediated by crystal-O over gold modified tungsten trioxide via photocatalysis

General indirect transformation of methane into formaldehyde is based on methanol as intermediate yet leading to low selectivity. Herein, we report a direct photocatalytic conversion of methane to formaldehyde over gold modified cuboid-shaped tungsten trioxide with exposed (002), (020) and (200) facets containing crystal-O at room temperature (25 degrees C). Under light irradiation, high spin state crystal-O ion as a hole can active C-H bond in methane and subsequently be consumed to form formaldehyde, then renovated by the addition of oxygen. Isotopic (CH4)-C-13 and O-18(2) tests reveal that formaldehyde indeed stems from the combination of methane and crystal-O on the exposed (002), (020) and (200) facets. Besides, metallic gold deposited on the surface of cuboid-shaped tungsten trioxide can extract the photoexcited electrons and further enhance the formation of crystal-O- ions. The productivity of formaldehyde over optimized catalyst can reach 7202 mu mol g(-1) with approximate 100 % selectivity within 24 h reaction time.

Automated summary

A direct photocatalytic conversion of methane to formaldehyde over gold modified cuboid-shaped tungsten trioxide with exposed crystal-O facets has been reported, achieving high productivity and selectivity of formaldehyde under room temperature conditions. The activation of C-H bonds in methane by high spin state crystal-O ions, combined with the extraction of photoexcited electrons by metallic gold, results in efficient formation of formaldehyde. Isotopic tests confirm the origin of formaldehyde from the combination of methane and crystal-O on the exposed facets.