Fabrication of hollow spheres of Co3O4 for catalytic oxidation of carbon monoxide

In this study, hollow Co3O4 spheres for the oxidation of carbon monoxide were fabricated using silica templates. The shells were formed by the precipitation of carbonate species on silica templates, and then leached in an aqueous sodium hydroxide solution for the removal of silica templates followed by calcination process. The effects of preparation conditions such as pH (=7-10) and calcination conditions were investigated. Homogeneous hollow Co3O4 spheres were obtained at pH value of 7.09, and high purity hollow Co3O4 spheres were obtained at calcination temperatures greater than 623 K. The samples calcined at temperatures less than 623 K included cobalt carbonate species, and the carbonate species converted into catalytically inactive cobalt oxyhydroxide after leaching in an aqueous sodium hydroxide solution. The samples calcined at temperatures greater than 623 K included pure Co3O4 phase even after leaching. In the samples calcined at temperatures greater than 623 K, the amount of surface Co3+ species decreased with calcination temperature, while those of surface Co2+ species increased with calcination temperature. The activity of the catalyst for the oxidation of carbon monoxide was found to depend on calcination temperature, and the highest activity was obtained over the hollow spheres calcined at 623 K. The results indicate that high purity of Co3O4 phase and the surface Co3+ species plays an important role for high activity. The hollow spheres also exhibited activity higher than those exhibited by Co3O4 coated on silica templates and Co3O4 nanoparticles, indicating that the hollow spheres are an effective catalyst compared with the supported catalyst and nanoparticle catalyst. (C) 2015 Elsevier B.V. All rights reserved.