Diving into the CO x Methanation Mechanism of CO and CO2 Mixtures Catalyzed by the Nanostructured NiO-CeO2 Catalyst.

The CO2 methanation process in the presence of CO is a catalytic challenge toward the abatement of CO2 emissions from industrial exhaust gases with the goal of producing CH4 as a clean fuel. Herein, the CO x methanation mechanisms of a NiO-CeO2 (Np) catalyst constituted by nickel oxide-cerium oxide nanoparticles with efficient operation under CO2 and CO + CO2 gas mixtures were addressed. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) analyses and 13C18O2 (49) pulse isotopic experiments reveal that solo CO2 methanation and comethanation (CO + CO2) present a common mechanism in which CO2 is transformed into *CO, from where the reaction proceeds. According to our outputs, inlet CO interferes with the CO2 methanation activity, delaying the reaction onset without selectivity impacts. Conversely, in the absence of CO2, the solo CO methanation performance is remarkably limited with poor CH4 selectivity. As demonstrated, the solo CO methanation mechanism is based on formates as key intermediates at low temperatures (<250 °C), while competitive CO2 production takes place onward. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) analyses conducted in synchrotron revealed a higher degree of reduction in the catalyst when CO and H2 are fed either alone or in combination with CO2, attributed to the CO oxygen abstraction capacity from the CeO2 phase. In the comethanation mixture, CO2 and CO are balanced in oxidation-reduction processes, yielding the maximum CO x conversion, while in the solo CO methanation, reductive processes prevail, limiting the CH4 formation.