Reactivity of CO₂ and H₂O on TiO₂ catalysts studied by gas phase FT-IR method and deactivation mechanism

The photoreduction of CO₂ to hydrocarbons is a sustainable energy technology that not only reduces emissions but also the need for alternative fuels. Wide band-gap TiO₂ catalysts are considered the most convenient candidates in terms of cost and stability. In this work, anatase TiO₂ powder was deposited on a silica filter paper, and photoreduction experiments were carried out in an FT-IR gas reactor using CO₂ gas with 50% relative humidity as the reactant under the irradiation of a high pressure Hg lamp. CH₄ and CO were detected as the CO₂ reduction products. However, there was a gradual decrease in the amounts of CH₄ and CO that were produced, seemingly because of the deactivation of the anatase TiO₂ surface. We analyzed the surface chemical states using XPS analysis to consider the cause of the TiO₂ deactivation, and found that the amounts of −OH group had increased on the TiO₂ surface after Hg lamp irradiation. Considering the analysis results, we assumed a surface deactivation mechanism.