(127a) CO2 Reduction over Metal Cluster/TiO2 photocatalysts

We previously showed how highly dispersed clusters of Cu on TiO₂ could be synthesized using a redox reaction between Cu²⁺ and Sn²⁺[1]. Such clusters were active for CO₂ reduction. Several other experiments have also shown CO₂ conversion activity using metal clusters[2,3]. The ability to synthesize supported metal atoms and clusters to initiate CO₂ reduction could lead to cheaper, efficient single-site catalysts. In the current work we modeled using density functional theory (DFT) several metal clusters on TiO₂ in order to understand and predict catalytic activity of these materials.

A key activation step in CO₂ reduction is the formation of bent CO₂ anion species. We initially modeled small Cu_x (x=1-4) clusters on a TiO₂ anatase surface. Our results do indeed show that Cu is able to activate CO₂ into a bent configuration that can be further reduced. Charge analysis indicates that CO₂ becomes negatively charged in a bent configuration, but not in a linear adsorption mode. We analyzed charges on Cu to assign its oxidation state, as well as calculating adsorbed CO vibrational modes, a common experimental method to assign oxidation state of supported metals. Based on these results we extended our studies to other supported metal clusters, such as Pt, Pd, and Ni. By systematically modeling a large number of supported metals we are able to identify how and which metal clusters may activate CO­₂. Such knowledge is crucial towards refining and designing better catalysts for CO₂ conversion.

(1) Liu, C.; Iyemperumal, S. K.; Deskins, N. A.; Li, G. J. Photonics Energy 2016, 7, 12004.

(2) Vajda, S.; White, M. G. ACS Catal. 2015, 5, 7152–7176.

(3) Liu, C.; Yang, B.; Tyo, E.; Seifert, S.; DeBartolo, J.; von Issendorff, B.; Zapol, P.; Vajda, S.; Curtiss, L. A. J. Am. Chem. Soc. 2015, 137, 8676–8679.