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|Type:||Artigo de periódico|
|Title:||Structural characterization of catalytically active metal nanoclusters in poly(amide imide) films with high metal loading|
|Abstract:||Noble metal clusters were generated and stabilized in poly(amide imide) (PAI) polymers in high dispersion and high concentration of typically 15 wt %. The loaded polymers were prepared as pore-free, mechanically stable membranes, which have been successfully tested for catalytic activity in membrane reactors. Pure Pd- and Ag-loaded as well as bimetallic Pd/Ag, Pd/Cu, Pd/Co, and Pd/Pb PAI films were investigated by means of X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to characterize the structure and morphology of the metal clusters in the protective polymer. The measurements consistently show a homogeneous distribution of metallic nanoclusters of 1-3 nm size with a smaller amount of larger aggregates up to 30 nm in some of the films. The precise cluster size and distribution critically depend on the solvents used (N-methyl-2-pyrrolidone, tetrahydrofuran) as well as on other preparation parameters such as the stirring time of the metal precursor/polymer solution. In the 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 the CuCl2 and CoCl2 precursors reacts with Pd, which may influence the Pd catalytic behavior. Reduction of the oxidized metal nanoclusters by H-2 at 300 K is quantitatively studied by means of XAFS and gas permeation. Optimum membrane preparation conditions are discussed with respect to the cluster formation mechanism.|
|Editor:||Amer Chemical Soc|
|Citation:||Journal Of Physical Chemistry B. Amer Chemical Soc, v. 101, n. 8, n. 1279, n. 1291, 1997.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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