Abstract

Surface properties and catalytic activity changes of Pd/SiO2 catalysts prepared by sol-gel processing have been investigated by means of evaluation of specific surface area, porosity, metal dispersion, surface acidity and surface composition. As comparison, Pd/SiO2 catalysts prepared by impregnation of SiO2 obtained by the sol gel method, were also studied. Both series of catalysts were tested in cycles of methane combustion. It has been found that the pH of gelation modifies strongly the porosity and surface area of the catalysts. However, no significant changes were observed in the metal dispersion. XPS results showed that for the catalysts obtained by the sol gel procedure, the Pd/Si surface atomic ratio does not change before and after the combustion cycle. However, in those catalysts prepared by the impregnation method, a significant decrease in the Pd/Si ratio was observed. The catalytic activity in the methane combustion under stoichiometric mixture of diluted CH4/O2 was studied at different temperatures from 473 K up to the temperature required for a total conversion for all catalysts in absence and presence of variable amount of water vapor. The poisoning effects of water is detected in all the catalysts and no effect of particle size was detected.