Investigating the Role of TiO2 and MgTiO3 Supports in ZnO-Catalyzed Photocatalytic CO2 Reduction

It is widely known that ZnO's photocatalytic activity on CO2 reduction with water is enhanced when it is supported. We investigated how the support affected the photocatalytic reduction of CO2 using ZnO supported by TiO2 and MgTiO3 catalysts. As a function of both the loading concentration and the support's specific surface area, the ZnO showed a variety of crystalline phases on the supports. Increased catalytic activity led to greater dispersion of ZnO particles and an increase in specific surface area. The rates of production for H-2 and CO, the main byproducts of CO2 reduction, exhibited distinct crystalline phase dependence. Specifically, H-2 production was mostly dependent on alpha-ZnO, but the rate of CO production grew with an increasing gamma-ZnO/alpha-ZnO ratio and reached its maximum at a certain gamma-ZnO/alpha-ZnO ratio. The two primary findings are as follows: (1) the photocatalytic activity is greatly improved when ZnO particles are loaded as rods on the support in quantities of a few tens of nanometers, and (2) a new mechanism is discovered whereby the reduction of CO2 adsorbed on gamma-ZnO or the interface between the two phases is dominated by water splitting on alpha-ZnO.