Kinetic Insights into Methanol Synthesis from CO₂ Hydrogenation at Atmospheric Pressure over Intermetallic Pd₂Ga Catalyst

This study presents a single-site microkinetic model for methanol synthesis by CO₂ hydrogenation over intermetallic Pd₂Ga/SiO₂. A reaction path analysis (RPA) combining theoretical results and realistic catalyst surface reaction data is established to elucidate the reaction mechanism and kinetic models of CO₂ hydrogenation to methanol and CO. The RPA leads to the derivation of rate expressions for both reactions without presumptions about the most abundant reactive intermediate (MARI) and rate-determining step (rds). The formation of H₂COOH* is found to be the rds (step 19) for methanol synthesis via the formate pathway, with CO₂ and H-atoms adsorbed on intermetallic sites as the MARIs. The derived kinetic model is corroborated with experimental data acquired under different reaction conditions, using a lab-scale fixed-bed reactor and Pd₂Ga/SiO₂ nanoparticles prepared by incipient wetness impregnation. The excellent agreement between the experimental data and the kinetic model (R² = 0.99) substantiates the proposed mechanism with an activation energy of 61.52 kJ mol^-1 for methanol synthesis. The reported catalyst exhibits high selectivity to methanol (96%) at 1 bar, 150 °C, and H₂/CO₂ ratio of 3:1. These findings provide critical insights to optimize catalysts and processes targeting CO₂ hydrogenation at atmospheric pressure and low temperatures for on-demand energy production.