Photocatalytic Activity of Ga2O3 Supported on Al2O3 for Water Splitting and CO2 Reduction

We have examined the photocatalytic activity of Ga2O3 supported on Al2O3 (Ga2O3/Al2O3 catalyst) without a noble metal cocatalyst for water splitting and reduction of CO2 with water under UV light irradiation by changing the loading amount of Ga2O3. All prepared Ga2O3/Al2O3 catalysts show photocatalytic activities for both water splitting and CO2 reduction, and their activities are significantly improved compared to those of nonsupported Ga2O3 and Al2O3. The water splitting is dominated for Ga2O3/Al2O3 with less than 1.0 vol % of Ga2O3 loaded, whereas the CO2 reduction, for higher Ga2O3-loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga2O3/Al2O3 catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga2O3 rods dispersed on an Al2O3 support consisting of a little distorted alpha-Ga2O3 phase. On the other hand, the CO2 reduction proceeds on sub-micrometer-sized Ga2O3 particles consisting of mixed phases of alpha-Ga2O3 and gamma-Ga2O3 or with appearance of boundaries between the alpha and gamma phases, which plays a critical role. Al2O3 used as the support of the Ga2O3 particles does not seem to play an important role in the photocatalytic CO2 reduction.