Mechanistic insights into the structure of CoCu bimetallic catalysts for CO2 hydrogenation into formate†

Abstract

Direct hydrogenation of CO₂ to valuable chemicals and fuels is a promising pathway for the valorization of detrimental CO₂. This study delves into the mechanistic insights of CO₂ hydrogenation into formate over bimetallic cobalt–copper on silica support catalysts (Co_xCu/SiO₂, x: 0–2). CoCu/SiO₂ with a Co and Cu molar ratio of 1 : 1 showed the best activity for CO₂ hydrogenation into formate with a maximum yield of 2.3 mmol g⁻¹ h⁻¹, and it exhibited 100% selectivity for formate and a turnover frequency (TOF) of 625.2 h⁻¹ in NaOH media. The formate formation rate over CoCu/SiO₂ was 2.5 times higher than the sum of those over monometallic Cu and Co catalysts. Combining X-ray absorption spectroscopy and transmission electron microscopy results provided insights into the active sites at the interface between cobalt and copper in CO₂ hydrogenation into formate. Theoretical calculations clarified and highlighted that the rate determining step was the formation of a carbonate intermediate on the CoCu bimetallic composite during the CO₂ conversion into formate. This work provides a theoretical reference for designing an efficient and cost-effective CoCu bimetallic catalyst for producing formate from CO₂.