Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl2 aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl2 solutions of lower acidity PPyOH was oxidatively doped and Pd-0 and Pd2+ were incorporated into the polymer matrix. Pd2+ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd-N bond). Additionally, deprotonation of PPyOH occurred in the PdCl2 solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl3(H2O)](-) on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)-palladium systems prepared in similar PdCl2 solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process. PPyOH was less reactive towards palladium species in the PdCl2 solutions of higher acidity where [PdCl4](2-) was the dominant complex. PPy-palladium. systems containing exclusively Pd2+ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid-base reaction or coordination of palladium ions by the polymer chain (Pd-N bond formation). Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts. (C) 2003 Elsevier Ltd. All rights reserved.