Microcalorimetric Study of the Absorption of Hydrogen by Palladium Powders and Carbon-Supported Palladium Particles

The adsorption and absorption of hydrogen on and in various forms of supported and unsupported palladium were studied using heat-flow calorimetry. The supports were found to have a tremendous effect on the nature of the hydrogen-palladium system. For palladium supported on silica or alumina, irreversible chemisorption was found to take place and be followed by bulk hydride formation. In contrast, it was found for carbon-supported particles that chemisorption does not take place and that the observed behavior could be explained by a model using only bulk hydride formation. It was further found that the heat of formation and equilibrium for β-hydride formation are functions of particle size. It was not clear if surface adsorption takes place on unsupported palladium.