A Pd-Bi Dual-Cocatalyst-Loaded Gallium Oxide Photocatalyst for Selective and Stable Nonoxidative Coupling of Methane

Nonoxidative coupling of methane (NOCM) is an attractive reaction for the direct conversion of methane to ethane and hydrogen. Although the conventional catalytic NOCM reaction needs high operating temperatures and thus suffers from the deactivation of the catalyst by coke formation, a photocatalytic NOCM reaction can take place at low temperature, even around room temperature. In the present study, a gallium oxide photocatalyst with a palladium and bismuth dual cocatalyst (Pd-Bi/Ga2O3) was found to exhibit high activity for selective NOCM, producing ethane and hydrogen from methane upon photoirradiation at nearly room temperature (ca. 320 K) and atmospheric pressure. The optimized Pd(0.18)-Bi(0.05)/Ga2O3 photocatalyst showed a high production rate of ethane of 1.10 μmol h–1, where the methane conversion was 0.03% within the contact time of 0.8 s, the reaction selectivity was as high as 97%, and the apparent quantum efficiency was 0.2%. The methane conversion exceeded the thermodynamic limitation. The Pd-Bi/Ga2O3 photocatalyst showed excellent stability for 100 h without significant loss of activity or selectivity. Its recyclability was also confirmed. The roles of the dual cocatalyst involving the interparticle transfer and a tentative reaction mechanism with the dual cocatalyst were also proposed.