Quantum chemical modeling of ground states of CO2 chemisorbed on anatase (001), (101), and (010) TiO2 surfaces

To design efficient CO2 photoreduction catalysts, we need to understand the intermediates and energetics of various reactions involved in the photoreduction of CO2 in greater detail. As a first step in this process, the ground states of CO2 chemisorbed on small clusters from various anatase surface planes are modeled in this study. We show that large basis sets with diffuse functions and high levels of electron correlation are needed to model the electron attached states of CO2, which may play a role in its photoreduction. Density functional theory (DFT) calculations Of CO2 adsorbed on small TiO2 clusters (Ti2O9H10) extracted from the (010), (001), and (101) surface plane structures point to the formation of different adsorbed species depending on crystal face atomic structure. The calculated infrared (IR) spectral properties of these species are compared against experimental data. We find favorable agreement for the existence of three different surface complexes. The formation of different surface species correlates well with the acid-base strength of the coordinatively unsaturated atoms. The implications of carbonate formation for CO2 photoreduction are discussed.