Dispersion of copper on ceria for the low-temperature water-gas shift reaction

Abstract Cu species in the forms of layers, clusters and particles were dispersed on a rod-shaped ceria by a deposition-precipitation method and the resulting Cu/CeO2 catalysts were tested for the low-temperature water-gas shift reaction. The structural, chemical and surface properties of the Cu/CeO2 catalysts were analyzed by spectroscopic and microscopic techniques. It was identified that dispersion of copper on the rod-shaped ceria strongly depended on the metal loading (1-28 mol%): lower contents resulted in copper monolayers and/or bilayers while higher loadings led to multi-layered clusters and faceted particles. The copper-ceria interface was constructed by an intimate bonding of positively-charged copper atoms with oxygen vacancies on ceria, in a form of Cu+-Ov-Ce3+, involving the electronic and geometric interactions between the copper atoms in the metal species and the oxygen vacancies on ceria. The overall activity increased linearly with the copper content in the range of 1-15 mol%, contributed mainly by copper monolayers and/or bilayers. Further increasing Cu loading up to 28 mol% only slightly enhanced the activity because of the presence of multilayered and crystalline Cu particles. This finding demonstrates that the dispersion of copper on the rod-shaped ceria depends on the loading of copper in the Cu/CeO2 catalysts, which is associated with the number and density of the active sites.