A NEW METHOD FOR THE DETERMINATION OF THE MONOLAYER CAPACITY FOR HYDROGEN ON A METAL SUPPORTED CATALYST BASED ON THERMODYNAMIC CRITERIA APPLIED TO THE EUROPT-1 REFERENCE CATALYST

The different methods used for the determination of the monolayer capa city from isotherm adsorption measurements have been applied to the H- 2 adsorption results on the EUROPt-1 reference catalyst. These are ana lysed to show how some of these methods are dependent upon experimenta l features such as the evacuation rate at the catalyst surface, the si ze of the catalyst sample. It is shown that isochore measurements, in contrast to isothermal measurements, allow determination of variations in the isosteric heat of adsorption Q(iso) over a large coverage rang e, and up to the monolayer saturation. The variations of Q(iso) with t he adsorbed amount allows us to propose a new way of determining the v alue of the monolayer capacity. The values determined by isothermal me asurements are discussed at the light of this new method.