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 ma-jor challenge in modern science. Formic acid is one of the most promising platform molecules. Photocatalysis proposes an attrac-tive route for methane partial oxidation under mild conditions. The radical mechanism of methane photocatalytic oxidation re-stricts the selectivity to target products. In this article, we propose a strategy to break conventional limitations of methane photocata-lytic 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-1 photocatalyst are achieved.

Automated summary

Direct conversion of methane into formic acid using photocatalysis is achieved by adding a thermocatalyst in a one-pot reactor. The methane is selectively converted into a mixture of C1 oxygenates using a cesium salt of phosphotungstic acid on titania photocatalyst, and then the oxygenates are selectively converted into formic acid using an alumina-supported ruthenium catalyst. A selectivity to formic acid of 85% and a productivity of 5 mmol g-1 photocatalyst are achieved at room temperature.