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

Recently, many studies have demonstrated that carbon dioxide can be converted to methane on TiO 2 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 CH 4 , CO and CO 2 , 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 Ti 3+ centers of TiO 2 structure. The yield of CH 4 or CO depends on the surface conditioning of titania: the formation of CH 4 is boosted by a presence of adsorbed HCl, while the formation of CO is boosted by adsorbed H 2 SO 4 .