Mechanistic Features of the CeO2-Modified Ni/Al2O3 Catalysts for the CO2 Methanation Reaction: Experimental and Ab Initio Studies

In this study, we investigated the Ni/CeO2/Al2O3 catalyst system to explore the influenceof differentsynthesis parameters on interfacial phenomena and their impact onCO(2) methanation. The focus was on the textural propertiesof alumina, ceria loading, and the synthesis method of supported Ni,in relation to the catalyst's activity and CH4 selectivity.Among the catalysts studied, Ni-20Ce/mpAl demonstratedpromising results, with an X (CO2) valueof 70% and S (CH4) value exceeding 94% at350 & DEG;C. We observed that medium- and high-porosity alumina facilitatedbetter ceria dispersion, while Ni-CeO2 cogrowth led tosmall Ni crystallites (& SIM;4 nm) that increased in size after8 h of reaction. This catalyst exhibited several advantageous featuresfor CO2 methanation, including a high concentration ofoxygen vacancies (confirmed through Raman studies) and a significantpresence of surface Ce3+ species (validated by XPS andEPR studies). It also displayed excellent carbonyl activation capacity,high H-spillover capability, and strong SMSI phenomena. CO2-TPD and charge transfer Bader analysis confirmed the basic (Lewis)character of the catalyst's surface. Specifically, Ce3+ species, along with Ni atoms, provided suitable dual sites for CO2 adsorption at the Ni-ceria interface, forming Ni & BULL;& BULL;& BULL;O-C-O & BULL;& BULL;& BULL;Ce3+ entities. Furthermore, our analysis using operando SSITKA-DRIFTSrevealed the active participation of both Ni and the support in theCO(2) methanation reaction, validating the ab initio studies.Notably, linear and bridged adsorbed CO species (COL andCO(B)) on the Ni surface, as well as bicarbonates (HCOOOs),were identified as active reaction intermediates involving Ce3+-OH and Al3+-OH entities. Comparingthe thermal stability of carbonate-type intermediates to that of carbonyls,a CO-mediated mechanism emerged as the predominant pathway over theNi-20Ce/mpAl catalyst.