Study of PdO species on surface of TiO2 for photoreduction of CO2 into CH4

Different percentage of PdO composited TiO2 photocatalysts (TiO2-PdOX%, X >= 1.5) are prepared using the sol-gel way. It can be revealed that the inducted Pd ions play a role of PdO surface species instead of entering into the TiO2 crystal lattice determined by the characterization measurements of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and High-resolution transmission electron microscopy (HRTEM). The behaviors of photogenerated electron-hole pairs and band structure of the synthesized TiO2-PdOX% (X >= 1.5) photocatalysts are investigated by Photoluminescence (PL), PL lifetime decay curves, XPS valence band (VB) spectra, the density-functional theory (DFT) calculation and UV-vis diffuse reflectance spectra. The TiO2-PdOX% (X >= 1.5) photocatalysts exhibit higher activity for conversion of CO2 to CH4 than pristine TiO2 due to the presence of PdO. The inactivation mechanism for TiO2-PdOX% photoreduction is also discussed. This work can further explain the influence of surface species on photocatalytic performance.