Photocatalytic reduction of CO2 over noble metal-loaded and nitrogen-doped mesoporous TiO2

Nitrogen-doped mesoporous TiO2 photocatalysts were developed for CO2 photoreduction by water in gas phase. The effects of nitrogen doping and noble metal loading were investigated in detail. The characteristics of samples were investigated by techniques, such as XRD, FT-IR, TEM, XPS, nitrogen adsorption–desorption, and UV–vis diffuse reflectance spectroscopy. The loading of noble metals (i.e., Pt, Au, and Ag) generally improved the photocatalytic activity, and the efficiency follows the order: Pt > Au > Ag. It was found that the loading of Pt also promoted the transformation of catalyst associated carbon residues to methane. With unique properties, such as the mesoporous structure, light absorption, and the electron transfer character, the nitrogen-doped mesoporous TiO2 samples showed good activity for CO2 photoreduction to methane under visible light. The optimum loading amount of Pt was 0.2 wt.%, and the optimum doping amount of N was 0.84% on the basis of the lattice oxygen atoms. Aspects such as the origination of visible light sensitivity in terms of nitrogen doping, the effect of noble metal loading, and the reaction mechanism were also discussed.

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► Nitrogen-doped mesoporous TiO2 samples are active for CO2 photoreduction.
► Molecularly chemisorbed nitrogen species contribute to the visible light sensitivity.
► Noble metals loading generally improved the photocatalytic activity.
► Pt showed the best promotion effect.