Photocatalytic nonoxidative coupling of methane on gallium oxide and silica-supported gallium oxide

Both unsupported and silica-supported gallium oxide were found to promote the nonoxidative coupling of methane (NOCM) to produce ethane and hydrogen upon photoirradiation at around room temperature. The unsupported gallium oxide demonstrated high methane conversion and high ethane selectivity in hydrocarbon products; however, the amount of hydrogen produced was not equivalent to the amount of ethane produced, because other reactions, such as consecutive coupling and coke/carbon formation, also would proceed. The gallium content on the silica-supported gallium oxide affected both the local structure of gallium species and the photocatalytic property. The sample with the lowest loadings of Ga (0.1 mol%), on which the gallium oxide existed mainly as highly dispersed tetrahedral species, exhibited high specific activity per Ga atom and high selectivity for NOCM, where ethane and hydrogen were produced in almost equal amounts. The gallium oxide clusters or nanoparticles on the silica-supported samples with Ga loadings of 0.5–10 mol% exhibited low selectivity, likely due to the variety of the active sites.