XANES investigations of Pd-doped polyaniline

Polyaniline doped with palladium (PANI–Pd) demonstrated a particular catalytic activity and selectivity in reaction of the hydrogenation of the triple C-C bond. Pd K-edge X-ray absorption near edge structure (XANES) studies were performed for PANI–Pd and several palladium compounds like PdCl2, (NH4)2PdCl4, Pd(NH3)4Cl2, (NH4)2PdCl6, K2PdCl4, [(C3H5)PdCl] 2, PdCl2(CH3CN)2 and PdO. The measurements were carried out in transmission mode at the station X1 in HASYLAB. Chemical shifts of Pd K edge for PANI–Pd and other palladium compounds were evaluated. The experimental XANES spectra were compared with the theoretical XANES spectrum calculated for PdCl2 by applying the FEFF8 program. It was found that the Pd K edge XANES spectrum for PANI–Pd was similar to that for ammonium tetrachloropalladate (NH4)2PdCl4. Our results indicated that in the PANI–Pd catalyst the tetrachloropalladate ion [PdCl4]?2 is coordinated to the amine part of the polymer chain and is responsible for specific catalytic properties.