THE EFFECT OF PD PRECURSOR AND PRETREATMENT ON THE ADSORPTION AND ABSORPTION BEHAVIOR OF SUPPORTED PD CATALYSTS

The behavior of carbon- and silica-supported Pd catalysts made from Pd acetylacetonate was compared to each other and also to carbon-support ed Pd prepared from PdCl2. Suppressed chemisorption and hydride format ion was observed after standard hydrogen reduction pretreatments at 57 3 K which was attributed to carbon contamination of the Pd bulk and su rface. Different treatments with oxygen in addition to pretreatment se quences with and without hydrogen reduction followed by hydrogen, oxyg en and carbon monoxide chemisorption or hydrogen and oxygen titration measurements were used to clarify the source of the carbon contaminant . Initial contamination due to the Pd(AcAc)(2) precursor was observed but it could be removed by calcination at 573 K in 4% oxygen; however, subsequent recontamination during reduction in hydrogen indicated tha t carbon atoms from the support could also be involved. Protecting the Pd surface with chemisorbed oxygen by cooling in oxygen prevented thi s carbon contamination. (C) 1998 Elsevier Science B.V. All rights rese rved.