A comparison of activated hydrogen chemisorption on some supported metal catalysts

Abstract

Hydrogen chemisorption on 10% Fe Al 2O 3 , 10% Fe SiO 2 , 10% Ni Al 2O 3 , and 5% Rh TiO 2 reduced at 473 and 773 K was compared using temperature-programmed desorption and, for two of these, using chemisorption isobars. Adsorption into the strongest states was slow at 300 K for each catalyst previously reduced at 723 or 773 K. The similarity of the effect for each catalyst suggets that they share a common cause. Decoration by reduced titania species is known to influence chemisorption; however, reduced alumina and silica species are not expected after reduction at 723 K. Estimation of the surface charge density due to charge transfer with the support suggests that this will never be of importance, except near the metal-support interface. It is suggested that decoration may have resulted after small amounts of SiO x and AlO x originally dissolved in the impregnating solution accumulated at the metal surface.