Theoretical investigation of carbon dioxide adsorption on MgH2 with a cobalt catalyst†

Abstract

This work presents a theoretical investigation of carbon dioxide (CO₂) adsorption on MgH₂ and its reaction (chemisorption) with cobalt doped MgH₂. The focus of this study is the properties and mechanisms involved in CO₂ adsorption on clean MgH₂ surfaces and the role of Co in enhancing the adsorption process. Density functional theory (DFT) calculations were performed to examine different CO₂ adsorption sites on the MgH₂ surface along with the adsorption distances, binding energies, and geometric parameters. The results indicate that physical adsorption of CO₂ occurs on MgH₂ with similar adsorption energies at different adsorption sites. The coverage effect of CO₂ molecules on MgH₂ was also investigated, revealing an increased affinity of CO₂ with higher surface coverage. However, excessive coverage led to a decrease in adsorption efficiency due to competing surface adsorption and intermolecular interactions. The orientation of adsorbed CO₂ molecules shifted from parallel to quasi-perpendicular arrangements upon adsorption, with notable deformations observed at higher coverage, which gives a hint of CO₂ activation. Furthermore, the study explores the CO₂ adsorption capacity of MgH₂ in comparison to other materials reported in the literature, showcasing its medium to strong affinity for CO₂. Additionally, the effectiveness of a single Co atom and Co clusters as catalysts for CO₂ adsorption on MgH₂ was examined. Overall, this theoretical investigation provides insights into the CO₂ adsorption properties of MgH₂ and highlights the potential of Co catalysts to enhance the efficiency of the methanation process.

Keywords: DFT; CO₂ conversion; Cobalt catalyst; Charge transfer.