DFT insights into defect-engineered Fe surfaces for CO2 dissociation and hydrogenation

Using density functional theory (DFT), we investigated two CO2-involving reactions on Fe surfaces: its dissociation into CO and O, and the formation of HCOO. These reactions represent the initial steps of CO2 hydrogenation pathways toward hydrocarbons and various oxygen-containing organic products. We modeled three different catalytic surfaces: (a) the pristine Fe(100) terrace, representing a defect-free surface; (b) the same plane with an Fe adatom (Fead); and (c) the Fe(310) surface, a zigzag-type facet formed by the intersection of the (100) and (110) planes. The reactions were simulated starting from the most stable CO2 adsorption modes on each surface. The results show that dissociation is more favorable on Fead-Fe(100) and Fe(310), with activation barriers approximately 20–25% lower than on Fe(100). In contrast, the highest activation barrier for hydrogenation is observed on Fe(310), attributed to the strong chemisorption of atomic H. The most interesting behavior is observed on Fead–Fe(100), which exhibits the lowest activation barriers for both reaction channels among the three surfaces, with hydrogenation being the kinetically preferred pathway. However, theoretical investigations explicitly focused on isolated adatoms remain scarce. The present results suggest that Fe adatoms may play a key role in enhancing CO2 activation on iron surfaces.