Platinum-loaded lanthanum-doped calcium titanate photocatalysts prepared by a flux method for photocatalytic steam reforming of methane

Calcium titanate (CaTiO3) samples were prepared by a flux method with various parameters such as selection of the flux, presence or absence of the flux, and solute concentration in the molten mixture with the flux. These conditions much influenced the structural and physical properties like morphology, particle size, specific surface area, and photoabsorption bands. The photocatalytic activity of the samples loaded with Pt-cocatalyst (Pt/CaTiO3) was evaluated for the photocatalytic steam reforming of methane around room temperature. It was found that the sample prepared with a KCl flux realized 3.3 times higher photocatalytic activity than that prepared by a conventional solid-state reaction method. Further, La-doping to the CaTiO3 photocatalyst (Pt/CaTiO3:La) was examined. It was revealed that the La cation was successfully doped at the Ca site in the CaTiO3 lattice. It is observed that small amount of La-doping anomalously enhanced the crystal growth although it lowered the photocatalytic activity. In contrast, the sample with a moderate amount of La-doping such as 1 mol % exhibited 1.6 times higher photocatalytic activity than the non-doped sample. Although most of the structural properties such as morphology, particle size and specific surface area could not simply explain the improvement of photocatalytic activity, at least it was revealed that the defects giving rise to the absorption bands in visible light region decreased the photocatalytic activity.