Photocatalytic methane conversion into chemicals and fuels under mild conditions Article Swipe

A cascade one-pot photo-chemo-catalytic process for methane oxidation to formic acid has been proposed. A specifically designed photocatalyst and a commercial heterogeneous catalyst were used together in the cascade process. The methane selective conversion into formic acid proceeds first over caesium salt of phosphotungstic acid (CsPW) supported on titania, which photocatalytically oxidizes methane under irradiation into a mixture of C1 liquid oxygenates. The C1 liquid oxygenates produced by photocatalysis are then selectively converted into formic acid over the heterogeneous alumina supported ruthenium catalyst. All reactions of selective oxidation of methane to formic acid occur in the cascade process at room temperature in the same reactor. The cascade process produced formic acid with a productivity of 5000 μmolformic acid g-1photocatalyst and a selectivity of 85 %, as well as a concentration of up to 1.1 mmol L-1.Gold nanoparticles with a size from 6 to 29 nm supported on titania have been prepared for photocatalytic non-oxidative and oxidative methane coupling in both batch and continuous gas flow reactors. The photocatalytic performance is not affected by the nanoparticles size. The methane conversion requires band gap transition in TiO2 excited by UV irradiation. No methane conversion was observed after activation of plasmonic gold nanoparticles by visible light. The plasmonic effect of gold nanoparticles cannot alone drive the methane photocatalytic conversion. The methane activation and oxidation occur over titania oxygen vacancies, while oxygen is likely activated by gold nanoparticles. The methane conversion was facilitated by slower electron-hole recombination in the presence of gold nanoparticles. A hydrocarbon productivity of 1864 μmol g−1 h−1 with a coupling selectivity higher than 86% was achieved in the continuous oxidative methane coupling flow process.Silver salt of phosphotungstic aicd (AgPW) supported on titania has been prepared for photochemical methane coupling. The methane conversion requires band gap transition in both the AgPW and TiO2 by UV irradiation as well the charge transfer between them with intimate contact. Introducing even small amount of AgPW to TiO2 significantly enhanced the coupling rate. During photochemical methane coupling, cationic Ag+ species were reduced to metallic Ag and resulted in photoactivity decrease, while Ag+ species and photoactivity can be regenerated from the spent AgPW-TiO2 exposing to light in the presence of air. The chemical looping process achieved ethane production of 64 μmol/g with coupling selectivity above 95%.