Photocatalytic transformation of CO2 to CH4 and CO on acidic surface of TiO2 anatase

•CO2 reduction to CH4 is more efficient in presence of adsorbed protons.•Titania prepared by hydrolysis of TiCl4 calcinated at low temperature is very efficient material.•In absence of any acid methane concentration remained under detection limit.

Recently, many studies have demonstrated that carbon dioxide can be converted to methane on TiO2 surface by a photocatalytic process. We show that such a photo-reduction can be significantly affected by the presence of an acidic proton in powder samples of titania. Using in situ absorption gas-phase rovibrational spectroscopic detection of CH4, CO and CO2, we demonstrate that proton enhancement positively affects transformation of intermediate derivatives to methane during the photo-irradiation process via several reactions in which the electron transfer inside titania is coupled to oxygen transfer to the Ti3+ centers of TiO2 structure. The yield of CH4 or CO depends on the surface conditioning of titania: the formation of CH4 is boosted by a presence of adsorbed HCl, while the formation of CO is boosted by adsorbed H2SO4.

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