Structure of the Grafted Polyethylene-Based Palladium Catalysts: WAXS and ASAXS Study

Abstract

Wide and anomalous small-angle X-ray scattering (WAXS, ASAXS) methods were used to study the structure of the grafted polyethylene-based palladium catalysts and to find out how the grafting material, polystyrene, poly(acrylic acid), or poly(4-vinylpyridine), affects the structure of the catalyst. The Pd content of the samples was about 5% and Pd(II) was reduced to Pd(0) using the same reducing agent, HCHO. The starting polyethylene fiber was semicrystalline and this structure was not destroyed in the different preparation processes. Pd salts did not crystallize in the samples and the smallest Pd(II) particles were formed in the poly(4-vinylpyridine) grafted sample. Pd(0) crystallites with the average sizes of 35 and 60 Å were formed in the poly(acrylic acid)- and polystyrene-grafted samples, respectively, after reduction of Pd(II) to Pd(0). The poly(4-vinylpyridine)-grafted reduced sample did not contain Pd(0) crystallites. Pd(0) particles showed a tendency to be smaller than Pd(II) particles. The volume distribution of Pd(0) particles of the polystyrene-grafted sample was heterogeneous and indicated a large population of particles with the radii of 60−250 Å. For the poly(acrylic acid)-grafted sample the volume distribution was bimodal, containing maxima at 17 and 58 Å. The smallest Pd(0) particles were formed in the poly(4-vinyl pyridine)-grafted sample and the maxima of the distribution were at 9 and 20 Å.