Effect of Co/Cu Ratio and Na Promotion on CO2Hydrogenation to Alcohols over CoCu/MgAl2O4Catalysts

Abstract

CO2 is one of the primary greenhouse gases, and its catalytic hydrogenation to ethanol represents a promising strategy for both CO2 mitigation and the production of value-added chemicals. However, the high thermodynamic stability of CO2, along with the challenges of C–C coupling and selectivity control, makes this transformation particularly demanding. In this work, we investigate a series of Co10-xCux/MgAl2O4 catalysts (x = 0, 1, 5, 9, and 10, with total metal loading of 10 wt %) as catalysts for CO2 hydrogenation to alcohols, exploring the impact of chemical composition and metal–oxide interfacial properties. Insights from related reactions, such as ethanol steam reforming (ESR) and the reverse water gas shift (RWGS) reaction at ambient pressure, were used to support the understanding of Co and Cu site roles in CO2 hydrogenation. Among the tested catalysts, prereduced Co5Cu5 exhibited the highest performance under high-pressure conditions, achieving productivities of 29 mg MeOH gCoCu–1 h–1 and 6 mg EtOH gCoCu–1 h–1. A prereduction step led to the formation of a CoCu alloy and modifications in the Co/Cu surface ratio, which contributed to enhanced catalytic activity. Co5Cu5 displayed the best balance between activity and selectivity, while Na promotion enabled C2+ alcohol formation, demonstrating the tandem action of Cu0 and CoCu alloy sites. These findings highlight the synergistic effects of Co–Cu interactions and alkali metal promotion in tuning catalyst reducibility and improving selectivity toward higher alcohols.