Comparative study of the activities of supported Pd catalysts in decomposition of ozone and oxidation of methane

The catalysts activities in ozone decomposition and complete oxidation of methane were compared. The content and macrodistribution of palladium on the spheres were varied by using different concentration of free chloride in the impregnation solution and by varying time of impregnation. The number of exposed atoms was obtained by selective chemisorption of CO at room temperature. For the samples with the eggshell distribution, increasing of Pd content is followed with the decrease of Pd dispersion, and at the same time with the increase of Pd layer thickness. Also, the observed Pd dispersion drop is not in accordance with the increase of Pd content. In the sample with uniform Pd macrodistribution almost atomic dispersion is obtained. The Pd mean crystallite size or Pd-dispersion is affected both by palladium content and thickness of Pd layer. It should be assumed that the number of participating palladium atoms would depend on the thickness of the deposited noble metal layer, and there would be an optimum thickness. Therefore, effective use of the noble metal will be realized when during the synthesis an optimum correlation between the Pd content, the active surface area and the layer thickness is achieved.