Catalysis and the Adsorption of Hydrogen on Metal Catalysts

Abstract

Publisher Summary This chapter discusses the catalysis and the adsorption of hydrogen on metal catalysts. The adsorption (chemisorption) of hydrogen on clean metal surfaces is almost always accompanied by absorption of hydrogen into the interior of the structure. This absorption is a slow activated process, and has in the past been mistaken for activated adsorption of hydrogen on the surface. The heat of absorption of hydrogen is considerably lower than the heat of chemisorption. The heats of chemisorption of hydrogen on nickel and iron are nearly identical and decrease from about 30,000 calories for the sparsely covered surface to about 18,000 calories for the completely covered surface. The heat of chemisorption on tungsten decreases from 45,000 calories to about 13,000 calories as a function of surface coverage. The heat of adsorption of hydrogen on metals has been found to be constant over wide temperature ranges. The activation energy for the chemisorption of hydrogen on all metals studied is extremely low. The decrease of heat of adsorption as a function of surface coverage can be explained satisfactorily by interaction of the adsorbed atoms with each other.