Insight into CO2 methanation mechanism over NiUSY zeolites: An operando IR study

Ni-impregnated USY zeolites with increasing Ni content (5, 10, 14%wt.) were investigated by operando IR spectroscopy for both CO2 adsorption and CO2 methanation conditions reaction. In-situ FTIR and TPD experiments highlighted a rather weak CO2 adsorption, which occurs namely as carbonates or CO2 linear complexes over cations (e.g., Na+). Under methanation conditions, dissociated hydrogen reacts with carbonates and/or physisorbed CO2, leading to monodentate formates, then carbonyls (both adsorbed onto Ni0 particles), and finally to methane. A detailed mechanism of the pathways involved in CO2 methanation over NiUSY catalysts is then discussed in accordance with infrared spectroscopic data.