ON THE NATURE OF THE INTERACTION OF H2PDCL4 WITH THE SURFACE OF GRAPHITE-LIKE CARBON MATERIALS

Adsorption of H2PdCl4 from aqueous solutions on the surface of graphit e-like carbon materials proceeds through two competitive pathways: red uction, which gives rise to Pd-0 particles of 6-100 nm in size, and fo rmation of pi-complexes of PdCl2 with > C = C < fragments of the carbo n matrix: PdCl2/C + 2HCl <((2))under left arrow> H2PdCl4 + C (1) under right arrow Pd/C + 2Cl/C + 2HCl Process (1) is localized near the ext erior surface of the porous carbon particles. Process (2) takes place on the whole surface of these particles. The quantitative ratio of the adsorbed palladium species (Pd2+ and Pd-0) and also the dispersion an d morphology of the metallic particles depend on the mode of contact o f the H2PdCl4 solution with the carbon, the composition of the gas pha se, the size of the carbon particles, the chemical state of the carbon surface and the conditions of drying. The results obtained are explai ned in terms of the electrochemical theory of carbon reactivity. Copyr ight (C) 1997 Elsevier Science Ltd.