Selective CO2 Hydrogenation to Methanol by Halogen Deposition over a Cu-Based Catalyst

The hydrogenation of carbon dioxide to methanol represents a promising pathway for both mitigating greenhouse gas emissions and producing valuable platform molecules. CuO-ZnO-Al₂O₃ (CZA) is the catalyst used for the methanol production from CO₂ due to its high activity under relatively mild conditions. Coproduction of CO reduces the methanol selectivity in CO₂ hydrogenation. In this work, the CZA catalyst has been promoted with halogens (Br, Cl, or I) using halobenzene precursors. The promotion with bromine significantly improves the methanol selectivity compared to the pristine catalyst. The effect was observed at different amounts of halogen deposited over the catalyst surface. A combination of characterization techniques and kinetic analysis enabled us to explain the effects of halogen on the catalytic performance. The presence of varying halogen amounts in the CZA catalyst enhances methanol selectivity in two ways: by suppressing the reverse water–gas shift reaction and by hindering methanol decomposition to CO.