Abstract

Crosslinked poly(4-vinylpyridine-co-styrene) was synthesized by radical polymerization. Catalysts having 1 wt% Pd were obtained by impregnation of a copolymer, poly(4-vinylpyridine-co-styrene) with a Pd colloidal dispersion. We modified metal particle sizes by changing the aging period of the colloidal dispersion, with the average size in the range of 2.5-4.3 nm. The most probable structure of the metal cluster attached to the polymers is described. X-ray diffraction, transmission electron microscopy (TEM), and H2-O2 titrations were used as characterization techniques. The H2 consumption during titration was extremely low, and the calculated metal dispersion was between 15 and 25 times lower than those estimated from TEM. This suggests that the Pd crystals were almost completely covered by the polymer. The vapor-phase hydrogenation of toluene on resins supported Pd catalysts were studied. The catalysts in the hydrogenation of toluene exhibited low activity, and the obtention of significant selectivities to partial hydrogenation products (close to 60 mol%) was remarkable. The results are explained in terms of a significant decrease in the hydrogenation capacity due to the coverage of metal particles by the resin.