Revealing the Effect of Sodium on Iron-Based Catalysts for CO₂ Hydrogenation: Insights from Calculation and Experiment

The promotional effects of sodium on Fe₅C₂ catalysts for CO₂ hydrogenation were systematically investigated by a synergistic combination of density functional theory (DFT) calculations and experimental methods. Na was found to markedly alter the electronic structure of Fe₅C₂ surface, leading to a reduction of the CO₂ dissociation barrier from 0.45 to 0.08 eV and a decrease of the hydrogen binding energy. Moreover, Na lowers methane’s selectivity by hindering further hydrogenation of CH₂ and enhances C–C coupling probability by promoting the chain growth of CH₂. Additionally, Na strengthens alkenes’ selectivity by facilitating dehydrogenation of alkyls and boosting the desorption of alkenes. The theoretical findings were confirmed by experimental results. Adding Na to Fe₅C₂ catalyst was found to facilitate CO₂ conversion and alkenes’ selectivity. Especially, the O/P (olefin/paraffin) ratio of C₂–C₄ hydrocarbons increases from 2.0 to 9.7 and the C₅₊ hydrocarbons’ selectivity increases from 12.6% to 51.8%. This study further deepens the understanding of the promotional effect of sodium on Fe-based catalysts for CO₂ hydrogenation and enlightens the rational design of highly selective catalysts.