Roles of Silver Co-catalyst on Gallium Oxide for Photocatalytic CO₂ Reduction to CO

抄録

It is well known that Ag loaded Gallium oxide (Ag/Ga₂O₃) promotes photocatalytic CO₂ reduction to CO. However, the role of the Ag co-catalyst in the CO₂ reduction has not been clarified. We have intended to find the relationship between the state of Ag loaded on Ga₂O₃ and their activity for the photocatalytic CO₂ reduction. To achieve this, we have tried to control and stabilize the loading state of Ag on Ga₂O₃ during their use for the photocatalytic CO₂ reduction by adding methanol as a reducing agent. It is confirmed that methanol stabilizes the particle sizes of Ag nanoparticles (Ag-NPs) loaded on Ga₂O₃ under the photocatalytic CO₂ reduction condition and is hardly decomposed to produce CO. Using Ga₂O₃ loaded with size-controlled Ag-NPs as a photocatalyst for the CO₂ reduction, it is found that Ag-NPs with their sizes within 10—30 nm are active sites for the photocatalytic CO₂ reduction and the catalytic activity linearly increases with the increase of the number density of Ag-NPs. However, a higher Ag loading amount over 1.0 wt% promotes aggregation of Ag to be larger metal particles over 70 nm which are not active for the CO₂ reduction.