Photo-catalytic reduction of carbon dioxide (CO2) into hydrocarbons is an attractive approach for mitigating CO2 emission and generating useful fuels at the same time. Titania (TiO2) is one of the most promising photo-catalysts for this purpose, and nano-structured TiO2 materials often lead to an increased efficiency for the photocatalytic reactions. However, what aspects of and how such nano-materials play the important role in the improved efficiency is yet to be understood. Using first principles calculations, reaction mechanisms on the surface of bulk anatase TiO2(101) and of a small TiO2 nano-cluster were investigated to elucidate the role of four-fold coordinated titanium atoms and quantum confinement in the CO2 reduction. Significant barrier reduction observed on the nano-cluster surface is discussed in terms of how the under-coordinated titanium atoms and quantum confinement influence CO2 reduction kinetics at surface. It is shown that the reduction to CO can be greatly facilitated by the under-coordinated titanium atoms, and they also make CO2 anion formation favorable at surfaces.
This work appeared in The Journal of the American Chemical Society.