CO2-to-methanol conversion through catalytic hydrogenation: Mechanistic Insights and Microkinetic Modeling on Zirconia-Promoted Cu/ZnO/Al2O3 Catalyst

Abstract

This study investigates the catalytic hydrogenation of CO2 to methanol over Cu/ZnO/Al2O3 catalysts promoted with zirconia, integrating experimental characterizations, density functional theory (DFT) calculations, and microkinetic modeling. A key focus is placed on identifying the minimum energy pathway (MEP) for CO2 conversion, which proceeds through seven distinct reaction routes leading to the formation of hydroxy-methylene (HCOH), a crucial intermediate in methanol synthesis. Among these pathways, the carboxylic route (CO2 → COOH → C(OH)2 → HC(OH)2 → HCOH) emerges as the most energetically favorable, especially upon zirconia incorporation, with significantly lowered total reaction energies (ΔE). Zirconia enhances the catalyst's performance by increasing surface basicity, oxygen vacancies, and copper reducibility, thereby facilitating CO2 activation and hydrogenation. The microkinetic model, grounded in DFT-derived mechanistic insights and incorporating the dominant MEP, accurately predicts product outlet mole fractions across various operating conditions. These findings highlight zirconia's pivotal role in optimizing catalytic pathways, improving methanol yield, and suppressing undesired byproducts, thus advancing the design of efficient catalysts for sustainable methanol production from CO2.