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.
