Strong Stabilization of Co Nanoparticles by CeO_2-x Clusters in Inverse CeO_x/Co Catalysts for Enhanced CO₂ Methanation.

Abstract

Inverse catalysts, where metal oxide species are dispersed over metallic nanoparticles, represent a promising class of materials for accelerating various chemical reactions. However, stabilizing metal nanoparticles with a small amount of oxide clusters remains a significant challenge, as the metallic phase tends to sinter under reaction conditions due to insufficient immobilization. In this study, flame spray pyrolysis is employed to synthesize uniformly sized inverse CeO_x/Co catalysts for CO₂ methanation (Sabatier reaction). It is found that small, highly reducible CeO_2-x clusters effectively stabilize metallic cobalt nanoparticles, thereby preventing sintering even during hydrogen reduction at 500 °C and during CO₂ hydrogenation. Detailed operando characterization demonstrates that this stabilization leads to a high density of metallic Co sites interfaced with CeO_2-x clusters, which facilitates CO₂ activation into carbonyl (CO^*) intermediates, resulting in significantly enhanced CH₄ formation rates. Notably, an inverse CeO_x/Co catalyst containing 20 mol% Ce exhibits a methanation rate an order of magnitude higher than that of a CeO₂-free Co catalyst. These findings highlight the dual role of CeO_2-x clusters in both stabilizing Co nanoparticles and enhancing catalytic performance, offering a robust strategy for improving CO₂ hydrogenation performance.