Modulating the electronic state of Cu over Cu/ZnO/SBA-15 catalysts for boosting methanol synthesis from CO2

Abstract

Methanol synthesis via CO2 conversion is a “green carbon” route for mitigating the greenhouse effect and recycling carbon resources. However, despite the widespread use of copper-based systems for methanol synthesis in recent decades, the chemical state of the active Cu species remains controversial. In this study, various Cu/ZnO/SBA-15 catalysts possessing different interfacial structures were engineered by atomic layer deposition (ALD). The optimized Cu/50c-ZnO/SBA-15 afforded the highest mass-specific methanol formation rate of 211.7 gMeOH·kgcat−1·h−1 under the conditions of 250 °C and 3.0 MPa. In-depth characterizations indicated that the electronic state of Cu could be modulated by engineering the interfacial structures of the Cu/ZnO series catalysts, and the Cu cation sites (Cuδ+ and Cu+) are the active centers for methanol synthesis reaction rather than the Cu0 sites. Mechanistic analysis demonstrated that HCO3* and CO3* were slowly transformed to HCOO* and further hydrogenated to methanol following the formate-methoxy intermediate route. This work provides an improved understanding of the origin of the methanol synthesis active centers and emphasizes the potential for fabricating next-generation Cu-based catalysts via ALD.