Heterogenized palladium chitosan complexes as potential catalysts in oxidation reactions:: study of the structure

Complexes of palladium with chitosan were prepared by different methods such as coprecipitation and adsorption and studied by EXAFS, FTIR, and X-ray photoelectron spectroscopy (XPS). It was found in the case of the coprecipitation-type complex that a chelate structure is a likely state of palladium. In the case of the adsorption-type system, palladium is coordinated by two chitosan NH2 groups without chelatization. It is evident from the EXAFS and XPS data that the structure of the complexes changes in the course of palladium reduction. In the case of the complex prepared by coprecipitation, Pd(0) atoms presumably form trimers in a polymer matrix; the formation of dimeric structures seems to be most typical of the adsorption complex. XPS data show the possibility of reversible redox transformations of palladium immobilized on a chitosan matrix. The complexes prepared can be considered as potential oxidation catalysts. (C) 2003 Elsevier B.V. All rights reserved.