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DFT thermodynamic study of the adsorption of CO<inf>2</inf> and H<inf>2</inf>O on W<inf>3</inf>O<inf>x</inf>/M(1 1 1) (x = 6 or 9 and M = Cu, Ag or Au). Insight for the water-gas shift reaction

Abstract:

DFT calculations were performed to study the adsorption of CO2 and H2O on the inverse W3Ox/M(1 1 1) catalysts (x = 6 and 9, M = Cu, Ag and Au). Upon adsorption of W3Ox on Cu(1 1 1), Ag(1 1 1) and Au(1 1 1), the results indicate that the stoichiometry of the oxides determines the direction of the charge transfer. That is, the W3O6 and W3O9 are oxidized and reduced after the adsorption on the surfaces, respectively. The CO2 is adsorbed at the oxide-metal interfaces of W3Ox/M(1 1 1) in a bent configuration, except on W3O9/Au(1 1 1) where it is not adsorbed due to a lack of available electrons on the Au(1 1 1) surface. After the adsorption, the CO2 molecule receives electrons from both the oxide and the surface which leads to the formation of CO2δ− at the oxide-metal interface. The stoichiometry of the W3Ox is very important in the adsorption of H2O since the molecular and dissociative adsorptions on W3O9/M(1 1 1) are exothermic and endothermic, respectively, but on W3O6/M(1 1 1) both adsorption types are exothermic, and the dissociation of H2O is slightly energetically more favourable than molecular adsorption on W3O6/Au(1 1 1). Lastly, a thermodynamic profile for the water-gas shift reaction catalysed by W3O6/M(1 1 1) was performed, and we found that the overall reaction is exothermic and that the W3O6/Au(1 1 1) systems seems to be the most active due to the favourable dissociation of H2O.