Copper Promoted Cobalt and Nickel Catalysts Supported on Ceria-Alumina Mixed Oxide: Structural Characterization and CO Oxidation Activity

Catalytic activity of CoO, NiO, CuO-CoO, and CuO-NiO nanocrystalline mono- and bimetallic catalysts over a thermally stable and high surface area ceria-alumina mixed oxide Support was evaluated for oxidation of carbon monoxide at normal atmospheric pressure and lower temperatures. The content of Co or Ni in the respective monometallic catalysts was 10 wt % and the Cu-promoted samples contained 5 wt % each. These catalysts were prepared by a wet impregnation procedure and the CeO2-Al2O3 Support was obtained by a deposition precipitation method. The synthesized catalysts were characterized by BET Surface area, X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns of 773 K calcined samples revealed the presence of metal oxide phases, namely, CeO2, CuO, NiO, and Co3O4 in the respective catalysts. However, after calcination at 1073 K, the XRD lines corresponding to CuO and NiO were absent. EDX results confirmed the actual amount of metal loadings in the respective catalysts. The H-2-TPR results suggested that Cu-doping accelerates and decreases the onset reduction temperature of monometallic samples. Raman results of 773 K calcined samples showed a prominent broad peak at 461 cm(-1) corresponding to the F-2g Raman active mode of CeO2. The TEM studies confirmed the presence of nanosized composite oxides with narrow size distribution of metal oxide particles. The XPS results disclosed the presence of Cu1+ species along with Cu2+ and the promotional effect of Cu in Co-containing samples to suppress the formation of the CoAl2O4 phase. Among different catalysts, the copper promoted CuC-NiC/CeO2-Al2O3 sample exhibited better activity for CO oxidation at lower temperatures, The better activity of the catalyst is attributed to the formation of well-dispersed and highly reducible metal oxide species over the mixed oxide support.