Methane coupling and hydrogen evolution induced by palladium-loaded gallium oxide photocatalysts in the presence of water vapor

Non-oxidative coupling of methane (NOCM, 2CH(4) -> C2H6 + H-2) is a reaction that can directly produce ethane and hydrogen at the same time, and gallium oxide (Ga2O3) powder has been reported as an effective photocatalyst for NOCM at room temperature. In this study, we investigated the reaction conditions for Pd-loaded Ga2O3 photocatalysts to improve the production rate of C2H6 and H-2. We found that the 0.1 wt% Pd/Ga2O3 exhibited high selectivity of C2H6 (75.8%, carbon-based) under the conditions of steam reforming of methane. Photocatalytic NOCM seems to proceed in the presence of small amount of water. An increase in water vapor pressure (P-H2O) was essential for the steady production of C2H6 and H-2. The C2H6 production rate was 0.79 mu mol min(-1) for 50 mg of Pd/Ga2O3 powder at P-H2O = 3.6 kPa. The apparent quantum efficiency (AQE) for C2H6 production was 5.1%, which is much higher than that of conventional photocatalytic NOCM in the absence of water vapor. The importance of water adsorbates on the photocatalyst surface was suggested by water vapor adsorption isotherm and Fourier transform infrared (FT-IR) spectroscopy. It is revealed that multilayered water molecules adsorbed on the photocatalyst surface play a role as a reaction field that promotes the dehydrogenative coupling of CH4. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study investigated the reaction conditions of Pd-loaded Ga2O3 photocatalysts for enhanced production of ethane and hydrogen, revealing the crucial role of water vapor in promoting the photocatalytic non-oxidative coupling of methane. The presence of water vapor was found to significantly increase the production rate of C2H6 and H-2, with an apparent quantum efficiency of 5.1% under certain conditions. Water adsorbates on the photocatalyst surface were suggested to play a key role in facilitating the dehydrogenative coupling of CH4.