Theoretical studies of the adsorption of CH4 on Ni-CeO2 systems: Evidence of a strong metal-support interaction

Abstract

Trabajo presentado en el 6th Workshop on Novel Methods for Electronic Structure Calculations, celebrado en La Plata (Argentina) del 12 al 14 de noviembre de 2015.Natural gas is one of the cheapest sources of energy available on the planet. Methane can be used directly for the production of heat and/or electricity or it can be used for the production of syngas a fuel gas mixture consisting primarily of hydrogen and carbon monoxide via a reforming processes. The dry reforming of methane (DRM), CH4+CO2 2CO+2H2, represents a very interesting approach both to valorize a cheap source or carbon (CO2) as well as to reduce the overall carbon footprint of the increasing worldwide fossil-based methane consumption. Efficient and not too expensive catalysts for the dry reforming of methane (DRM) reaction are sought. Selective and stable conversion remains challenging due to the need to activate methane and CO2, unravel the mechanism that sustains good activity and selectivity, and mitigate deactivation through carbon deposition. In this context model Ni/CeOx(111) catalysts were created. Ceria’ ability to stabilize reduced states by accommodating electrons in the localized 4f states is well known. Yet, finding the minimum energy structures with respect to both the localization of the electrons and the character of the 4fstate associated to each Ce3+ ion still represents a challenge in the theoretical modeling of reduced ceria systems using DFT. We here employ the DFT+U approach. We find that strong interactions between Ni and the reducible ceria support and the presence of oxygen vacancies are at the basis of the modifications of the oxidation state of Ni from Ni2+ [1] to Ni for clean and heavily reduced support, respectively. The results are consistent with Ni 3p XPS data for corresponding experimental model catalysts. Moreover, we correlate these changes with bonding properties of adsorbed CH4 and co-adsorbed CH3 and H.Peer Reviewe