ADSORPTION AND TEMPERATURE-PROGRAMMED DESORPTION OF HYDROGEN WITH DISPERSED PLATINUM AND PLATINUM-GOLD CATALYSTS

Hydrogen adsorption has been studied by temperature-programmed desorption (TPD) and by static volumetric measurement (SVM) on a range of supported dispersed platinum and platinum-gold catalysts. For compositions in the range Pt 98, Au 2 to Pt 15, Au 85 mole%, a comparison of hydrogen adsorption data with predictions from surface enrichment theory combined with electron microscopic particle size measurement, led to the conclusion that after suitable thermal treatment, equilibrium surface enrichment by gold was achieved, although equilibrium was most difficult to achieve for the Pt 15, Au 85 composition. It was concluded from the nature of the hydrogen adsorption isotherms that, at higher pressures, some hydrogen could be adsorbed on surface gold atoms, probably as a result of spillover from the platinum component. The general shape of the TPD profiles on platinum-gold was independent of gold content; to a first approximation the gold acted as an inert diluent. The implications of this result for the mode of hydrogen chemisorptive bonding are discussed. With gold-free platinum catalysts there was a trend towards an extension of the high temperature tail of the TPD profile with decreasing d ̄Pt in the range ≤4 nm, due to the presence of hydrogen binding states of higher energy. Possible reasons for this are discussed. Illustrations are given of the technique of TPD-profile dissection using increased starting temperatures. A TPD peak with a maximum in the region 700-750 K has been assigned to desorption from the support, this binding state being populated via hydrogen spillover from the platinum. © 1979.