Catalytic performance of transition metals (Co, Ni, Zn, Mo) doped CuO-Ce0.8Zr0.2O2 based catalysts for CO preferential oxidation in H2-rich streams

CuO-Ce0.8Zr0.2O2 composites (CuCZ) doped by transition metals (Co, Ni, Zn, Mo) as well as Co-doped CuCZ with different molar ratios of Co/Cu were prepared by a facile urea grind combustion (UGC) method and applied for CO preferential oxidation (CO-PROX) reaction in the hydrogen-rich gas mixtures. The characterizations of XRD, N-2 adsorption-desorption, SEM, TEM, XPS and H-2-TPR were used to investigate the difference in the catalytic behavior. Activity results found that the modification of Co had a positive influence on the catalytic activity of CuCZ and the optimal ratio of Co/Cu was 1/10, while the addition of Ni, Zn and Mo resulted in the decrease in the catalytic activities. XRD, SEM, H-2-TPR and XPS results proved that the catalytic behavior of CuCZ based catalysts largely depended on the properties and types of transition metals. The addition of Co into CuCZ led to the isomorphous substitution of Cu2+ and Ce3+ species via Co2+ and Co3+, and the redispersion of Cu species over CeO2 support promoted the generation of the highly dispersed Cu oxides. As a result, large amount of active Cu+ sites and the surface active oxygen were available. The negative effects caused by Ni, Zn and Mo species were originated from the decreased amount of highly dispersed Cu oxides, possibly due to the differences in the oxidation-reduction property, the ion radius, the metal-support interaction as well as the nucleation rate and the size growth of particles during the preparation process. Consequently, the structure-property relationship was established, and the catalytic activity was suggested to be correlated with the amount of highly dispersed Cu oxides. Furthermore, 1/10Co-CuCZ showed excellent stability in terms of both CO conversion and CO2 selectivity during 120 h time-on-stream test. (C) 2019 Elsevier B.V. All rights reserved.