Flame Synthesized Co-CeO Catalysts for CO Methanation.

Achieving selective conversion of CO to CO, CH, or CHOH remains a key challenge in catalyst design for CO 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-CeO 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 CeO nanoparticles with a high surface area and approximately 3.8 mol % Co ions strongly interacting with CeO. Catalysts with ≥5 mol % Co feature segregated CoO and CoO 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 CO/mol Co/s, CH selectivity 85%) was observed in 10 mol % Co-CeO, 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 Co-O-Ce sites that mainly favor CO formation (79% selectivity). Low Co content facilitates CO hydrogenation to CO and minor CHOH formation, likely on oxygen vacancies, assisted by H dissociation on very small metallic Co clusters. Larger Co nanoparticles predominantly produce CH, with minor CO and no CHOH. These results demonstrate that FSP enables tuning of catalyst structures for selective CO hydrogenation, leveraging the synergy between small metallic Co particles and Co-O-Ce sites.