STRUCTURAL CHARACTERIZATION OF CATALYTICALLY ACTIVE METAL-CLUSTERS INPOLYMER MEMBRANES

Metal clusters were generated and stabilized in pore free, mechanicall y stable poly(amide imide) (PAI) polymer membranes in high dispersion and high concentration of typically 15wt-%. These membranes have been successfully tested for catalytic applications. Pure Pd-loaded and bim etallic Pd/Ag, Pd/Cu, Pd/Co, Pd/Pb PAI films were investigated by mean s of x-ray absorption spectroscopy, small and wide angle x-ray scatter ing and transmission electron microscopy to characterize the structure of the metal clusters in the protective polymer. The measurements con sistently show a homogeneous distribution of metallic nanoclusters of 10-30 Angstrom size within the membranes. Also, a smaller amount of la rger aggregates up to 300 Angstrom is observed in most of the films. T he precise cluster size distribution critically depends on the solvent s used as well as on other preparation parameters such as the stirring time of the metal precursor/polymer solution. In case of Pd/Ag and Pd /Pb bimetallic films no clear evidence for the formation of bimetallic clusters in the membrane, i.e. alloying of both metal components, is found. In Pd/Cu and Pd/Co membranes, chlorine from CuCl2 and CoCl2 pre cursors reacts with Pd which may influence the Pd catalytic behavior. Reduction and oxidation of the metal nanoclusters is quantitatively st udied by means of x-ray absorption spectroscopy. Membrane properties a re discussed with respect to catalytic applications.