CO 2 methanation is an important probe reaction to understand CO 2 interactions with catalytic surfaces. Importance of this reaction is further increased by its association with CO 2 utilization. This study reports mechanistic aspects of CO 2 methanation over combustion synthesized Ru-substituted CeO 2 catalyst. Temperature programmed reaction experiments were carried out to understand the interaction of CO 2 , H 2 and their stoichiometric mixture with the catalyst surface. In situ FTIR spectroscopy was used to identify the intermediates of the reaction. It was observed that CO 2 adsorption took place on the surface of Ce 0.95 Ru 0.05 O 2 and the formation of surface carbonate intermediates took place only when H 2 was present in the gas phase. In absence of H 2 , CO 2 did not show any indication for chemisorption. This behavior was explained in terms of the reaction between CO 2 and the surface hydroxyls leading to formation of vacancy. Upon dissociation, carbonates led to chemisorbed CO which eventually formed methane upon reaction with gas phase H 2 . The exact identity of carbonate species and the pathway for methanation step were ambiguous following purely experimental studies. Density functional theory calculations were carried out to augment the experimental observations. Complete energy landscapes developed on the basis of differentiation of oxidized and reduced forms of the catalyst showed that the reaction followed a pathway consisting of surface carbonate species formed by the interaction of oxide surface and chemisorbed CO, and a sequential methanation via the surface methoxy species formation. The study provides physical insights into the role of oxidation state of the catalyst and the surface anionic vacancies in governing the reaction pathway.2

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