Effects of Al2O3 and MgAl2O4 Support on Photocatalytic Activity of Ga2O3 in CO2 Reduction with Water

It is known that photocatalytic activity of Ga2O3 on CO2 reduction with water is enhanced by employment of a support. However, the role of the support is not understood well. We have investigated the roles of the support on the photocatalytic CO2 reduction with using Ga2O3 supported by Al2O3 and MgAl2O4 as catalysts. On the supports, loaded Ga2O3 exhibited different crystalline phases and morphologies depending on the amount of loaded Ga2O3 on the supports and the specific surface areas of the supports. The larger the SSA, the more dispersedly Ga2O3 particles were loaded and gave higher catalytic activity. The production rates of H2 and CO, the dominant products of the CO2 reduction, showed different crystalline phase dependence, i.e., H2 production was dominated on α-Ga2O3, while the CO production rate increased with increasing the γ-Ga2O3/α-Ga2O3 ratio and peaked at a certain γ-Ga2O3/α-Ga2O3 ratio. Two main conclusions derived are, (1) Ga2O3 particles dispersedly loaded as a few tens nm sized rods on the support significantly enhance the photocatalytic activity and (2) a new mechanism that on α-Ga2O3 water splitting is dominated and resultant H atoms reduce CO2 adsorbed on γ-Ga2O3 or the boundary of the two phases.