EFFECT OF METAL-SUPPORT REACTION ON CARBURIZATION OF SUPPORTED CATALYSTS .2. PALLADIUM ON SILICA

The effect of high-temperature reduction (HTR) in hydrogen on the carburization of palladium in a commercial 5% palladium/silica catalyst was studied by X-ray powder diffraction. It was found that at 970 K an extensive reaction between the palladium and silica occurred with the formation of well-developed, crystalline palladium silicide (most probably Pd4Si). During subsequent annealing in acetylene at 550 K the palladium silicide remained inert, whereas non-reacted palladium formed a supersaturated palladium-carbon solid solution. Regeneration of the HTR palladium/silica catalyst by oxidation (770 K) - reduction (720 K) treatment transformed silicide back into palladium, but without its redispersion. The behavior of the palladium/silica catalyst is compared with that reported earlier for palladium/alumina.