Surface properties and catalytic activity changes of Pd/SiO2 catalysts prep
ared by set-gel processing have been investigated by means of evaluation of
specific surface area, porosity, metal dispersion, surface acidity and sur
face 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 th
at the pH of gelation modifies strongly the porosity and surface area of th
e catalysts. However, no significant changes were observed in the metal dis
persion. 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 impregnat
ion method, a significant decrease in the Pd/Si ratio was observed.
The catalytic activity in the methane combustion under stoichiometric mixtu
re of diluted CH4/O-2 was studied at different temperatures from 473 K up t
o the temperature required for a total conversion for all catalysts in abse
nce and presence of variable amount of water vapor. The poisoning effects o
f water is detected in all the catalysts and no effect of particle size was
detected.