Mechanism of methanol synthesis from CO₂ hydrogenation over Rh₁₆/In₂O₃ catalysts: A combined study on density functional theory and microkinetic modeling

In this study, the hydrogenation of carbon dioxide (CO₂) to methanol (CH₃OH) over Rh₁₆/In₂O₃ catalyst was studied through Density Functional Theory (DFT) and microdynamics modeling. The spontaneous dissociation mechanisms of H₂ and CO₂ adsorption at the Rh₁₆/In₂O₃ interface were investigated. The oxygen vacancies in In₂O₃ enhanced the adsorption process. Bader charge analysis revealed a marginal positive charge on Rh₁₆, elucidating the critical insights into the electronic characteristics and catalytic activity. The study established the RWGS+CO-Hydro pathway as the predominant mechanism for methanol synthesis, characterized by a sequential transformation of intermediates: CO₂*→COOH*→CO*+OH*→HCO*→CH₂O*→CH₂OH*→ CH₃OH*. Furthermore, Degree of Reaction Rate Control (DRC) analysis conducted in the range of 373-873 K and 10^-2 to 10³ Bar identified two principal kinetic phenomena: at lower temperature and higher pressure, the conversion of CO* + H* to HCO* significantly impacted the overall reaction rate. Conversely, at higher temperature, the step from CH₂O* + H* to CH₃O* was dominate.