Activation of CO2 at Chromia-Nanocluster-Modified Rutile and Anatase TiO2

2018-03-26T15:17:05Z (GMT) by Michael Nolan Marco Fronzi
Converting CO<sub>2</sub> to fuels is required to enable the production of sustainable fuels and to contribute to alleviating CO<sub>2</sub> emissions. In considering conversion of CO<sub>2</sub>, the initial step of adsorption and activation by the catalyst is crucial. In addressing this difficult problem, we have examined how nanoclusters of reducible metal oxides supported on TiO<sub>2</sub> can promote CO<sub>2</sub> activation. In this paper we present density functional theory (DFT) simulations of CO<sub>2</sub> activation on heterostructures composed of extended rutile and anatase TiO<sub>2</sub> surfaces modified with chromia nanoclusters. The heterostructures show non-bulk Cr and O sites in the nanoclusters and an upshifted valence band edge that is dominated by Cr 3d- O 2p interactions. We show that the supported chromia nanoclusters can adsorb and activate CO<sub>2 </sub>and that activation of CO<sub>2</sub> is promoted whether the TiO<sub>2</sub> support is oxidised or hydroxylated. Reduced heterostructures, formed by removal of oxygen from the chromia nanocluster, also promote CO<sub>2</sub> activation. In the strong CO<sub>2</sub> adsorption modes, the molecule bends giving O-C-O angles of 127 - 132<sup>o</sup> and elongation of C-O distances up to 1.30 Å; no carbonates are formed. The electronic properties show a strong CO<sub>2</sub>-Cr-O interaction that drives the interaction of CO<sub>2</sub> with the nanocluster and induces the structural distortions. These results highlight that a metal oxide support modified with reducible metal oxide nanoclusters can activate CO<sub>2</sub>, thus helping to overcome difficulties associated with the difficult first step in CO<sub>2</sub> conversion.