Facilitating Methane Conversion and Hydrogen Evolution on Platinized Gallium Oxide Photocatalyst through Liquid-like Water Nanofilm Formation

F. Amano, A. Ishikawa, H. Sato, C. Akamoto, S.P. Singh, S. Yamazoe, T. Sugimoto

Catal. Today, accepted.

The dehydrogenative coupling of methane, an approach aimed at converting methane into valuable chemicals like ethane and hydrogen, can be facilitated under ambient thermal conditions using semiconductor photocatalysts. Herein, we present an efficient continuous-flow photocatalytic system for methane conversion by inducing the formation of physically adsorbed water nanofilms on the surface of a Pt-loaded Ga2O3 photocatalyst. The microscopic properties of the adsorbed water were examined by diffuse reflectance infrared (IR) spectroscopy and ab initio molecular dynamics (AIMD) calculations. In comparison to the photocatalytic systems employed for non-oxidative coupling of methane, the presence of the interfacial water resulted in a 90-fold and 500-fold enhancement in the production rate of hydrogen and ethane, respectively. The rate of ethane formation significantly increased with water vapor pressure (PH2O) under a high methane pressure (PCH4) of 200 kPa. The selectivity for ethane reached 65% based on carbon content at PH2O = 3 kPa and PCH4 = 200 kPa. Through diffuse reflectance IR spectroscopy, volumetric water vapor adsorption analysis, and AIMD calculations conducted under the reaction conditions, we observed the formation of a liquid-like water nanolayer on the Ga2O3 surface at 300 K. Thus, this strategy of inducing water nanofilms affords a highly efficient photocatalytic system for hydrogen and ethane production.