Design of active sites in Ni/CeO2 catalysts for the methanation of CO2: tailoring the Ni-CeO2 contact

The role of different active sites on Ni/CeO2 catalysts in the CO2 methanation has been studied. Two types of active sites have been identified: CO2 chemisorption and dissociation sites at the NiO-ceria interface and H2 dissociation sites on Ni0 entities. Additionally, the proportion of these active sites has been optimized to maximize the activity. For these purposes, Ni/CeO2 catalysts with different proportion of active sites were prepared varying the Ni-incorporation method and controlling the structure of the ceria support in order to modify the NiO-ceria interaction. According to XPS, the optimal proportion of both sites required to achieve the maximum conversion was 25% Ni0 and 75% NiO-ceria for H2 and CO2 dissociation, respectively. In situ DRIFTS and Isotopic experiments with 13C18O2 showed that this optimal catalyst keeps the catalyst surface clean of carbon intermediates under reaction conditions, while surface bicarbonates are accumulated on a catalyst with an excess of active sites for CO2 chemisorption/dissociation.