Insights into a Nitrogen-Doped Cobalt Oxide Catalyst for Enhanced Hydrogenation of CO2 to C2+ Hydrocarbons

Hydrogenation of CO2 to C2+ hydrocarbons over non-noble metal catalysts is essential from environmental and economic aspects. However, increasing the selectivity of C2+ hydrocarbons is still challenging for Co-based catalysts, as their predominant selectivity is toward CH4 (>99%). Herein, this work provides insights into the mechanism of CO2 hydrogenation over a N-doped Co3O4 (CoNxOy) catalyst with a higher CO2 conversion (25%) and C2+ hydrocarbon selectivity (42 C-mol%) compared to the Co3O4 parent material (9% and 3 C-mol%, respectively). An increased concentration of oxygen vacancies and a decreased surface basicity strength in CoNxOy correlated with its enhanced catalytic performance. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations revealed the evolution of reaction intermediates and the N-doping benefits on the CoNxOy catalyst for high activity toward C2+ hydrocarbons. The findings were consistent with a CO2 hydrogenation catalytic cycle, where CO and C2+ hydrocarbons are mainly produced through carbonate and formate reaction pathways, respectively. Overall, we found that a relatively simple nitridation procedure can enhance the catalytic activity and selectivity of cobalt oxide toward higher hydrocarbons. This methodology could be extended to improve other transition metal-based catalysts for CO2 conversion.