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

- Ce is present as well dispersed CeO2 and Ni as Ni° particles after pre-treatment.
- CO2 adsorption capacity increases drastically after Ce addition on NiUSY catalyst.
- Hydrogen and bidentate carbonates appear to be the reactive species leading to formate.
- Adsorbed formates seem to be the “true” intermediate involved in the reaction pathway.
- The mechanism on NiCeUSY does not pass through the formation of CO.

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 CO2 adsorption and under methanation conditions (H2:CO2/4:1) reaction. In situ FTIR and CO2-TPD experiments highlighted that CO2 adsorption is rather poor over NiUSY zeolite, whereas CO2 uptake over CeNiUSY leads to the formation of a large amount of adsorbed carbonates on the CeO2 surface. Mechanistic pathways involved in CO2 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 CO2 hydrogenation reaction.

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