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

Abstract

Hydrogenation of CO 2 to C 2+ hydrocarbons over non-noble metal catalysts is essential from environmental and economic aspects. However, increasing the selectivity of C 2+ hydrocarbons is still challenging for Co-based catalysts, as their predominant selectivity is toward CH 4 (>99%). Herein, this work provides insights into the mechanism of CO 2 hydrogenation over a N-doped Co 3 O 4 (CoN x O y ) catalyst with a higher CO 2 conversion (25%) and C 2+ hydrocarbon selectivity (42 C-mol%) compared to the Co 3 O 4 parent material (9% and 3 C-mol%, respectively). An increased concentration of oxygen vacancies and a decreased surface basicity strength in CoN x O y 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 CoN x O y catalyst for high activity toward C 2+ hydrocarbons. The findings were consistent with a CO 2 hydrogenation catalytic cycle, where CO and C 2+ 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 CO 2 conversion.