The promoting effect of Ce in the CO2 methanation performances on NiUSY zeolite: A FTIR In Situ/Operando study

Abstract The behavior of 5% wt. Ni-impregnated and 5% wt. Ni-15% wt. Ce-impregnated zeolites (of USY type) were investigated by in situ / operando IR spectroscopy, both for CO 2 adsorption and under methanation conditions (H 2 :CO 2 /4:1) reaction. In situ FTIR and CO 2 -TPD experiments highlighted that CO 2 adsorption is rather poor over NiUSY zeolite, whereas CO 2 uptake over CeNiUSY leads to the formation of a large amount of adsorbed carbonates on the CeO 2 surface. Mechanistic pathways involved in CO 2 methanation over CeNiUSY catalyst are discussed in accordance with infrared spectroscopic data. Under methanation conditions, hydrogen is dissociated on Ni° particles and reacts with hydrogen and bidentate carbonates, leading first to the formation of monodentate formates, and then to methane, by further hydrogenation. No adsorbed carbonyls onto Ni° were detected while a large amount of formates was highlighted from 150 °C. The formate decomposition appears to be a kinetic relevant step to the observed kinetics of the CO 2 hydrogenation reaction.