Synergy of Cu(I) and oxygen vacancies in CO₂ hydrogenative coupling to ethanol on Cu/CeO_2−x catalysts

Hydrogenative coupling of CO₂ to ethanol presents a sustainable pathway for carbon neutralization, yet the fundamental active sites and reaction pathway/mechanism remain unclear. Here, we investigate CO₂ hydrogenative coupling over Cu/CeO_2−x catalysts, achieving an optimal CO₂ conversion of ~ 5% and ethanol selectivity of ~ 95% under 30 atm, H₂/CO₂ = 3, at 240 °C, and gas hourly space velocity (GHSV) = 120 mL·g_cat⁻¹·h⁻¹. We revealed that both Cu(I) and oxygen vacancies (O_v) serve as active sites, with turnover frequencies (TOFs) of 0.23 h⁻¹ per O_v site and 3.97 h⁻¹ per Cu(I) site, respectively. We also concluded that neither Cu(I) nor O_v can function independently; both Cu(I) and O_v are required for CO₂ activation and ethanol formation. Operando Fourier-transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations identify CH₂OH* and CH₂* as key intermediates in the C–C coupling step. These findings establish a mechanistic framework for CO₂ hydrogenative coupling and provide valuable insights for designing more efficient catalysts for ethanol synthesis from CO₂ conversion.