Regulating the content of Cu+ in Cu/CeO2 catalysts for the reverse water–gas shift reaction

Abstract

The prominence of Cu/CeO₂ catalysts in the RWGS reaction stems from Cu⁺ species and Cu–O–Ce solid solution (active toward both CO₂ and H₂). However, a reduction process is required for catalyst activation, which potentially causes excessive Cu⁺ reduction to Cu⁰ and damage to the Cu–O–Ce structure. Herein, the Cu⁺ content in Cu/CeO₂ is tuned by adjusting the H₂/Ar ratio during the reduction process, while ensuring the preservation of the Cu–O–Ce solid solution structure. The catalyst reduced in an atmosphere with a H₂ molar fraction of 0.25 exhibits the maximum content of oxygen vacancies and retains the highest surface Cu⁺ proportion (76.93%, as determined by Auger spectroscopy). This catalyst exhibits high CO₂ conversion (49.89% at 500 °C, H₂/CO₂ = 4 : 1) and low activation energy in the RWGS reaction. The Cu⁺ species and oxygen vacancies are essential to activating CO₂ and H₂, and the RWGS reaction follows the formate pathway with and HCOO* acting as intermediates. This study offers guidance for designing Cu-based catalysts for the RWGS reaction by exploring pretreatment conditions.