Unraveling the Role of Cu⁰ and Cu⁺ Sites in Cu/SiO₂ Catalysts for Water‐Gas Shift Reaction

Abstract

Abstract CuO x /SiO 2 precursor was successfully fabricated by an ammonia evaporation hydrothermal method. Upon reduction in 5 vol % H 2 /N 2 at 250, 300, 350, 400, or 450 °C, CuO and copper phyllosilicate species in the precursor bring about the formation of highly dispersed Cu 0 and Cu + species, respectively. The Cu + /Cu 0 ratios were studied by XAES technique, while the particle sizes were estimated on the basis of HRTEM images. It is disclosed that the ratios and particle sizes varied with CuO x /SiO 2 reduction temperatures. The results of in situ DRIFTS and XAES characterization reveal that both Cu 0 and Cu + are active for CO adsorption and water dissociation, especially so with Cu 0 and Cu + particles of small sizes. It was also observed that the adsorption of CO on Cu + is stronger than that on Cu 0 , and Cu 0 is more active than Cu + for water dissociation. Among the prepared Cu/SiO 2 catalysts, the one resulted from precursor reduction at 300 °C shows the highest CO conversion in WGS reaction, which is attributed to the small size of Cu 0 (2.45 nm) and the large amount of Cu + .