CO2 Conversion to Alcohols over Cu/ZnO Catalysts: Prospective Synergies between Electrocatalytic and Thermocatalytic Routes

The development of efficient catalysts is one of the main challenges in CO2 conversion to valuable chemicals and fuels. Herein, inspired by the knowledge of the thermocatalytic (TC) processes, Cu/ZnO and bare Cu catalysts enriched with Cu+1 were studied to convert CO2 via the electrocatalytic (EC) pathway. Integrating Cu with ZnO (a CO-generation catalyst) is a strategy explored in the EC CO, reduction to reduce the kinetic barrier and enhance C-C coupling to obtain C2+ chemicals and energy carriers. Herein, ethanol was produced with the Cu/ZnO catalyst, reaching a productivity of about 5.27 mmol.g(cat)(-1).h(-1) in a liquid-phase configuration at ambient conditions. In contrast, bare copper preferentially produced C-1 products like formate and methanol. During CO2 hydrogenation, a methanol selectivity close to 100% was achieved with the Cu/ZnO catalysts at 200 degrees C, a value that decreased at higher temperatures (i.e., 23% at 300 degrees C) because of thermodynamic limitations. The methanol productivity increased to approximately 1.4 mmol.g(cat)(-1).h(-1) at 300 degrees C. Ex situ characterizations after testing confirmed the potential of adding ZnO in Cu-based materials to stabilize the Cu1+/Cu-0 interface at the electrocatalyst surface because of Zn and O enrichment by an amorphous zinc oxide matrix; while in the TC process, Cu1+ and crystalline ZnO prevailed under CO, hydrogenation conditions. It is envisioned that the lower *CO binding energy at the Cu-0 catalyst surface in the TC process than in the Cu1+ present in the EC one leads to preferential CO and methanol production in the TC system. Instead, our EC results revealed that an optimum local CO production at the ZnO surface in tandem with a high amount of superficial Cu1+ + Cu-0 species induces ethanol formation by ensuring an appropriate local amount of *CO intermediates and their further dimerization to generate C2+ products. Optimizing the ZnO loading on Cu is proposed to tune the catalyst surface properties and the formation of more reduced CO2 conversion products.