Photocatalytic reduction of CO2 with H2O on TiO2 and Cu/TiO2 catalysts

Photoinduced reduction of CO₂ by H₂O to produce CH₄ and CH₃OH has been investigated on wellcharacterized standard TiO₂ catalysts and on a Cu²⁺ loaded TiO₂ catalyst. The efficiency of this photoreaction depends strongly on the kind of catalyst and the ratio of H₂O to CO₂. Anatase TiO₂, which has a large band gap and numerous surface OH groups, shows high efficiency for photocatalytic CH₄ formation. Photogenerated Ti³⁺ ions, H and CH₃ radicals are observed as reactive intermediates, by ESR at 77 K. Cu-loading of the small, powdered TiO₂ catalyst (Cu/TiO₂) brings about additional formation of CH₃OH. XPS studies suggest that Cu⁺ plays a significant role in CH₃OH formation.