Synergistic Cu+/Cu0 optimization via reduction-induced activation for water-gas shift reaction over Cu/Fe3O4 catalyst

Cu/Fe₃O₄ catalysts have excellent water-gas shift (WGS) reaction activity, which served as a replacement for toxic Fe-Cr HTS catalysts. In this study, a reduction-induced activation strategy was applied to synthesize Cu/Fe₃O₄ catalysts with controlled generation of Cu⁺ and Cu⁰ species. Systematic investigations demonstrated that increasing the reduction temperature from 250 to 400 °C not only raised the Cu⁺/(Cu⁰+Cu⁺) ratio but also reduced Cu nanoparticle size highly, thereby synergistically enhancing CO and H₂O adsorption-activation kinetics. The optimized Cu/Fe₃O₄ catalyst, reduced at 300 °C, exhibited outstanding WGS reaction activity, gaining a CO conversion of 93.9 % at 340 °C, which outperformed the reported commercial Fe-Cr catalysts. This superior performance can be attributed to a well-balanced Cu⁺/(Cu⁰+Cu⁺) ratio (45.0 %) and a refined nanostructure, characterized by ultrasmall Cu (9.29 nm) and Cu₂O (6.16 nm) nanoparticles. It was clarified that the optimal adsorption activation sites for CO and H₂O were at the Cu⁺ and Cu⁰ sites, respectively. What's more, synergistic effect of Cu⁺-Cu⁰ sites significantly accelerated the process of WGS reaction.