CO2 Activation and Hydrogenation: A Comparative DFT Study of Ru10/TiO2 and Cu10/TiO2 Model Catalysts

• Published in: Catalysis letters Vol. 147; no. 8; pp. 1871 - 1881
• Main Authors: Schlexer, Philomena, Chen, Hsin-Yi Tiffany, Pacchioni, Gianfranco
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2017; Springer Nature B.V
• Subjects: Activation; Activation analysis; Adsorption; Anatase; Carbon dioxide; Carbon monoxide; Catalysis; Chemistry; Chemistry and Materials Science; Hydrogen storage; Hydrogenation; Industrial Chemistry/Chemical Engineering; Metal clusters; Organometallic Chemistry; Physical Chemistry; Reduction (metal working); Surface chemistry; Titanium dioxide; Titanium oxides; Vapor phases; Nanoparticles < nanotechnology; Methanation; Cu; Ru; Methanol synthesis; valorization < processes and reactions; CO; Titania; hydrogenation
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-017-2098-1

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