The reactivity of defects at iron surfaces: theoretical study of carbon dioxide dissociation and hydrogenation on adatom and step sites

Abstract

This study presents the results obtained from studying the adsorption, dissociation, and hydrogenation of carbon dioxide (CO₂) on three iron (Fe) surfaces. Two of these surfaces are derived from the (100) plane: the pure terrace and the terrace with an added atom (adatom, Fe_ad-Fe(100)). The third surface corresponds to the plane Fe(310), which represents a stepped surface. The theoretical calculations were performed using the VASP calculation package, based on density functional theory (DFT), which is capable of representing extended surfaces. CO₂ finds more adsorption sites on surfaces containing topological defects, compared to the Fe(100) terrace. However, their adsorption energies improve slightly. The dissociation (CO₂→ CO + O) is more favorable on defected surfaces. The activation barrier for the hydrogenation (HCOO formation), is significantly reduced on Fe(100), but it is even lower on the Fe_adFe(100) surface. These results suggest that CO₂ hydrogenation is more likely to occur on Fe(100) and Fe_ad-Fe(100), whereas there will be competition between dissociation and hydrogenation on Fe(310).