Thermocatalysis enables photocatalytic oxidation of methane to formic acid at room temperature beyond the selectivity limits

Direct conversion of methane into fuels and chemicals remains a major challenge in modern science. Formic acid is one of the most promising platform molecules. Photocatalysis proposes an attractive route for methane partial oxidation under mild conditions. The radical mechanism of methane photocatalytic oxidation restricts the selectivity to target products. In this article, we propose a strategy to break conventional limitations of methane photocatalytic oxidation by adding a thermocatalyst and conducting the process in a one-pot reactor. In this strategy, the methane selective conversion into formic acid proceeds first over cesium salt of phosphotungstic acid on titania, which photocatalytically oxidizes methane into a mixture of C1 oxygenates. These oxygenates are then selectively converted into formic acid over a heterogeneous alumina-supported ruthenium catalyst. All reactions occur at room temperature in the same reactor. A selectivity to formic acid of 85% and a productivity of 5 mmol g−1photocatalyst are achieved.