Etude des systèmes à trois phases par diffusion centrale des rayons X

A theory for small-angle X-ray scattering by metallic supported catalysts is proposed. The expression leading to the determination of the solid granulometry is calculated in a way similar to the case of a two-phase system. As the Porod law must be followed, one can obtain from a study of both the support and the catalyst the specific area of the metallic phase. Experimental measurements have been performed on four metallic supported catalysts containing various amounts of platinum deposited on non-porous silica. In the case of low concentration, the dispersion of the metal is good and the X-ray results are in good agreement with those of electron microscopy. For high values of the concentration, the metallic area, measured by small-angle scattering, is the only parameter which characterizes the platinum dispersion.