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.