Cu Deposited on CeOx-Modified TiO2(110): Synergistic Effects at the Metal-Oxide Interface and the Mechanism of the WGS Reaction

Abstract

Experimental techniques and DFT calculations have been combined to study and compare the effect of the metal-substrate interaction in Cu/TiO2(110) and Cu/CeOx/TiO2(110) catalysts for the water-gas shift (WGS) reaction. Experiments and theory show that CeOx nanoparticles affect the dispersion of copper on titania, and on the formed copper-ceria interface, there are synergistic effects which favor water dissociation and the WGS reaction. The minimum energy path for the WGS reaction on the new highly active catalytic system Cu/CeOx/TiO2(110) has been predicted by theoretical calculations. Main steps such as adsorption-dissociation of water and∗OCOH carboxyl intermediate formation-deprotonation have been characterized. In this very particular system, water splitting is no longer the rate-limiting step because it can dissociate overcoming an energy barrier of only 0.92 kcal/mol. One important insight of the present work is to show that easy full hydration of the ceria particles strongly lowers the reaction barrier for the deprotonation of the∗OCOH intermediate and facilitates the evolution of the WGS reaction. For the first time, a system has been found on which the WGS reaction is able to work with all the involved energy barriers below 12 kcal/mol. This remarkable behavior makes the metal/CeOx/TiO2 family a potential candidate for industrial application as catalysts in the WGS reaction. The change in the metal-support interactions when going from Cu/TiO2 to Cu/CeOx/TiO2 illustrates the importance of optimizing the oxide phase when improving the performance of metal/oxide catalysts for the WGS.