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

CuOx/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 degrees 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 CuOx/SiO(2)reduction temperatures. The results ofin situDRIFTS 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 degrees 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+.