Kme. Attyia et Ne. Fouad, THERMOANALYTICAL AND SPECTROSCOPIC STUDIES OF THE SYNTHESIS OF SUPPORTED PALLADIUM CATALYST IN A H2 PDCL2/SIO2 PARENT SYSTEM/, Journal of thermal analysis, 42(6), 1994, pp. 1207-1219
A 5 wt% Pd/SiO2 catalyst was synthesized by heating PdCl2-impregnated
SiO2 in H2 at 300-degrees-C for 2 h. It was found that the metal parti
cle dispersion is improved when the reduction step is preceded by calc
ination at 300-degrees-C for 2 h. Thermogravimetry of the impregnated
support in air, N2 and H2 atmospheres was used to monitor the interact
ions occurring during the various preparative steps (i.e. drying, calc
ination and reduction) of the catalyst. The solid product of each prep
arative step was characterized by X-ray diffractometry and UV/Vis diff
use reflectance spectroscopy. The results indicate that following the
drying step (at 110-degrees-C in air) the palladium occurs in two dete
ctable forms: PdCl2 particles and Si-O-Pd(n+) surface species. The cal
cination appears to transform the PdCl2 particles into the latter surf
ace species. The H2-reduction eventually converts the surface species
into finely-dispersed Pd-degrees metal particles (average size = 8-14
nm). No other reduction products, such as PdySix, were detected.