Flame Synthesized Co–CeO2 Catalysts for CO2 methanation

Achieving selective conversion of CO2 to CO, CH4, or CH3OH remains a key challenge in catalyst design for CO2 hydrogenation. Site-specific activity at the metal–support interface plays a crucial role, motivating efforts to optimize metal particles and their interactions with supports. In this study, we synthesized Co-CeO2 catalysts with varying Co contents via flame spray pyrolysis (FSP) to investigate how the location and structure of Co influence activity. All samples contain ∼8 nm CeO2 nanoparticles with a high surface area and approximately 3.8 mol % Co2+ ions strongly interacting with CeO2. Catalysts with ≥5 mol % Co feature segregated CoO and Co3O4 particles, which are partially reduced to metallic Co at 300 °C. The highest Co-weight-normalized activity at 200 °C (3.9 ± 0.2 mmol CO2/mol Co/s, CH4 selectivity 85%) was observed in 10 mol % Co-CeO2, with ∼50% Co reduction and 4–5 nm Co nanoparticles. The 2.5 mol % Co sample exhibited only 10% reduction, forming small Co clusters and creating Co2+–O–Ce sites that mainly favor CO formation (79% selectivity). Low Co content facilitates CO2 hydrogenation to CO and minor CH3OH formation, likely on oxygen vacancies, assisted by H2 dissociation on very small metallic Co clusters. Larger Co nanoparticles predominantly produce CH4, with minor CO and no CH3OH. These results demonstrate that FSP enables tuning of catalyst structures for selective CO2 hydrogenation, leveraging the synergy between small metallic Co particles and Co2+–O–Ce sites.