Inverse Co Catalysts for CO ₂ Methanation: Structural and Chemical Promotion by Metal Oxides

Inverse catalysts, where oxide clusters are deposited on metal surfaces, have recently attracted significant attention for CO 2 hydrogenation. Among them, inverse cobalt catalysts such as CeO 2 /Co have demonstrated promising performance in low-temperature CO 2 methanation. However, the influence of promoting oxides in cobalt-based inverse catalysts remains largely unexplored. Herein, we prepared inverse Co catalysts promoted by Ti, Zr, Ce, and Si using flame spray pyrolysis and evaluated their performance in CO 2 methanation. Defective ZrO 2− x and CeO 2− x clusters strongly stabilized Co nanoparticles during H 2 reduction, resulting in inverse ZrO 2 /Co and CeO 2 /Co catalysts with abundant metallic surface sites and robust CO 2 methanation activity. In contrast, inverse SiO 2 /Co, with fewer exposed metallic sites, exhibited moderate methanation activity, while inverse TiO 2 /Co was the least active due to strong metal-support interactions that suppressed Co surface exposure. Notably, the inverse CeO 2 /Co catalyst suffered severe deactivation at 300 °C due to extensive coke formation. CO 2 /CO co-feeding experiments and CO-IR spectroscopy revealed that carbon deposition occurred via irreversible CO-induced poisoning and the Boudouard reaction. The used catalysts could be regenerated by thermal treatment in pure CO 2, which removed coke via the reverse Boudouard reaction. This study provides a detailed understanding of promoter effects on the CO 2 methanation activity and stability in Co-based inverse catalysts.