Catalytic hydrogenation of CO2 to methanol over Cu-based catalysts: Active sites profiling and regulation strategy as well as reaction pathway exploration

The active sites of copper-based catalysts and their impacts on activity and selectivity are first examined in this work, after which an overview of the regulation of the active sites and the pathways for CO₂ hydrogenation reactions follows. The primary active sites influencing CO₂ conversion and methanol yield and selectivity include Cu⁺/Cu⁰ species, Cu-oxide interfaces, Cu surface defect sites and M-Cu alloys. Strategies including additive control, carrier effect, and morphological modification can alter the kind and distribution of active sites. The main intermediates in the hydrogenation of CO₂ to synthesize methanol are HCOO^⁎ and COOH^⁎. The main intermediates in the synthesis of methanol by CO₂ hydrogenation are carboxyl species (COOH^⁎) and formate species (HCOO^⁎). The formate pathway can be further divided into the HCOO^⁎ pathway and the r-HCOO^⁎ pathway, depending on the intermediate involved. In the formate pathway, the hydrogenation of formate is the rate-determining step in the synthesis of methanol by CO₂ hydrogenation. The carboxylate species pathway is subdivided into the RWGS+CO-Hydro pathway and the trans⁃COOH pathway. The rate-limiting steps for these two pathways are the formation of CO/HCO species and the dissociation of COHOH^⁎ species, respectively. The review serves as the foundation for further developing copper base methanol catalysts that are extremely active, highly selective, and stable.