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Colloidal Cu, Ni, and CuNi nanoparticles obtained through chemical reduction were impregnated onto γ‐Al2O3 to prepare supported catalysts. Conventional catalysts were also prepared for comparison through support impregnation with metal salt solutions. A combination of TEM and STEM, thermogravimetric analysis, powder X‐ray diffraction, X‐ray photoelectron spectroscopy, and N2 adsorption analysis was used to characterize the alumina‐supported nanoparticle catalysts. Monodisperse Cu and Ni nanoparticles were uniformly distributed on γ‐Al2O3 as observed by STEM equipped with a high‐angle annular dark field (HAADF) detector. The powder XRD and HAADF–STEM provided evidence supporting the formation of CuNi particles containing the Cu core and the CuNi alloy shell. The resulting supported Cu and Ni nanoparticle catalysts were found to be 2.5 times more active in the water–gas shift (WGS) reaction per unit mass of the active metal as compared with catalysts prepared by means of the conventional impregnation method. Supported Cu catalysts showed promising activity at low temperatures (125–250 °C), whereas supported Ni catalysts showed high activity at high temperatures (275–400 °C). The presence of a surfactant during the preparation of supported Cu nanoparticles resulted in a higher degree of Cu dispersion and thus enhanced WGS activity. Stabilized Ni/Ni(OH)2 nanoparticles were also synthesized to prepare well‐dispersed supported Ni catalysts. In the case of bimetallic catalysts, Cu5Ni5 catalysts showed a higher specific reaction rate per unit surface area of the active metal than did monometallic catalysts. These findings strongly suggested that supported Cu, Ni, and CuNi nanoparticle catalysts prepared from metal colloids are promising, highly active WGS catalysts.

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