The thermal reduction of both oxidised palladium foil and SiO2/Si(100)
supported palladium oxide particles, ranging in size from 3.5 to 13 n
m, was investigated with XPS. Equations were derived for the XPS inten
sities, measured at normal emission angles, of the particles which con
sisted of a metallic core and an oxidic skin. By applying these equati
ons on the spectra measured after each reduction step, the particle si
ze and the size of the metallic core were calculated. Measurements on
palladium foil showed that the oxide layer thickness decreases linearl
y with the reduction time up to the last monolayer oxide. The reductio
n rate of the surface oxide is about eight times lower than the reduct
ion rate of the bulk oxide. The growth of the metallic core in palladi
um oxide particles appeared to be linearly proportional to the surface
area. The reduction rate of the smallest particles was comparable to
the reduction rate of the surface oxide of the palladium foil. The lar
ger particles behave identical to the palladium foil.