Electricity-driven selectivity in the photocatalytic oxidation of methane to carbon monoxide with liquid gallium-semiconductor composite

Abstract

Metal co-catalysts in oxide semiconductors are essential to enhance photocatalytic reaction, but the selectivity is often low due to the conversion of the target molecules as more reactive in comparison with the reagents. Here, we explore the influence of electricity on the activity and selectivity of liquid gallium as a co-catalyst loaded in TiO2 and ZSM-5 supports the photocatalytic oxidation of methane. We first show that the polarization of the photocatalytic chips allows a more efficient wetting of liquid gallium into the semiconductor matrices, which increases the availability of the photogenerated charge carriers for reactions and improves the overall activity of the composites. More importantly, the oxide skin surrounding the spread liquid is found to be charged, resulting in a significant reduction of the CO oxidation. An increase of the CO selectivity from 10 % to 80 % upon polarization to 50 V, with a stable photocatalytic activity reaching 0.6 ± 0.01 mmol.g-1·h-1, makes the use of electricity quite appealing to tailor liquid metals in catalysis.