Reaction Dynamics of CO₂ Hydrogenation on Iron Catalysts Using ReaxFF Molecular Dynamics Simulation

The conversion of CO₂ to hydrocarbons using catalysts is a promising route to utilize CO₂ and produce more valuable chemicals in a sustainable manner. Recent studies have shown that iron-based catalysts perform well for the hydrogenation of CO₂. While the hydrogenation reaction mechanism in the gas phase is straightforward, when catalyzed by iron it has been demonstrated to involve various chemical transformations, and the selectivity and conversion are strongly dependent on the particle size. To further investigate the dependence of the reactivity of iron catalysts on cluster size, we performed reactive molecular dynamics simulations using the ReaxFF force field (ReaxFF-MD) for iron nanoclusters of various sizes in a CO₂ and H₂-rich environment. We demonstrated that the homogeneous hydrogenation of CO₂ was correctly described by this ReaxFF model. The dissociation mechanism of CO₂ on the Fe₄, Fe₁₆ clusters, and the bcc(100) Fe slab agrees with previous DFT results. The ReaxFF-MD simulations suggest a strong dependence of reactivity on the cluster size, with the Fe₄ cluster having the highest reactivity. We show that ReaxFF-MD provides a route to understand reaction mechanisms in these nonequilibrium reactive processes where fast processes and local minima are important.