摘要
Using DFT+U calculations with inclusion of van-der-Waals (vdW) forces, we studied CO 2 activation and the initial steps of CO 2 hydrogenation over Cu 10 and Ru 10 clusters supported on the TiO 2 anatase (101) surface. CO 2 is readily adsorbed and activated on the Ru cluster where direct CO 2 dissociation proceeds with a barrier of 0.8 eV. When H atoms are co-adsorbed on the Ru cluster, H-addition to CO 2 becomes preferred, as the best Ru sites for CO 2 dissociation are blocked. A H atom is added to the CO 2 molecule with formation of a formate [HCOO] species and an activation barrier of 1.2 eV. On Cu 10 /TiO 2 , only weak adsorption modes of the CO 2 molecule are found, whereas H 2 readily adsorbs on the Cu cluster. A reduction of the titania support does not significantly change this picture. Therefore, the only viable pathway for the CO 2 hydrogenation over Cu 10 /TiO 2 is the addition of a pre-adsorbed H atom to CO 2 coming from the gas phase. This corresponds to an Eley–Rideal mechanism for the H-association to CO 2 . The work shows the importance to consider the hydrogen coverage on the metal cluster as an important variable in modeling the CO 2 hydrogenation reaction. Graphical Abstract: [Figure not available: see fulltext.].