Promoting Effect of Potassium and Calcium Additives to Cerium-Zirconium Oxide Catalysts for the Complete Oxidation of Carbon Monoxide

The effect of potassium and calcium additives on the catalytic activity of the Ce0.8Zr0.2O2 system in the reaction of CO oxidation was studied. With the use of X-ray diffraction analysis, it was found that the Ce0.8Zr0.2O2 and Ce0.8Zr0.2O2-Ca,K samples contained a mixed oxide of cerium and zirconium; the presence of the independent phases of potassium and calcium compounds in the modified system was not detected. With the use of the low-temperature adsorption-desorption of nitrogen, X-ray photoelectron spectroscopy, and temperature-programmed reduction, it was established that the Ce0.8Zr0.2O2-Ca,K system (in spite of the fact that its specific surface area was lower than that of Ce0.8Zr0.2O2) contained more active oxygen on the surface; peroxide and superoxide complexes formed upon the chemisorption of O-2 can act as active oxygen species. This can be the reason for a higher efficiency of the Ce0.8Zr0.2O2-Ca,K system in comparison with that of the unmodified oxide. The results obtained indicate that the ash impurities of Ca and K can increase the catalytic activity of the biomorphic mixed oxides Ce0.8Zr0.2O2 prepared with the use of sawdust as a template.