Structure and Electronic State of PdCl2–CuCl2Catalysts Supported on Activated Carbon

Abstract

The structure and electronic state of PdCl2–CuCl2catalysts supported on activated carbon (AC) were characterized using XAFS techniques. On the basis of XANES of the CuK-edge, a majority of CuCl2supported on the activated carbon was found to be reduced to Cu+species, probably by the reduction sites on the support surface. The CuK-edge EXAFS and XANES results suggest that the Cu+species are coordinated with three Cl−anions irrespective of the presence of PdCl2. The EXAFS analysis of the PdK-edge showed the formation of Pd metal particles as well as Pd chloride species coordinated with three Cl−anions. These results are in conformity with the chemical analysis of the catalyst that indicates a considerable loss of Cl−on the adsorption of PdCl2or CuCl2on the activated carbon. It was found that the formation of Pd metal was strongly suppressed by the presence of CuCl2. The PdCl2/AC, PdCl2–CuCl2/AC, and CuCl2/AC catalysts showed CO oxidation activities at >400 K, >500 K, and >570 K, respectively. The addition of H2O promoted the reactions over PdCl2–CuCl2/AC. Comparing the catalytic properties with the XAFS results, it is considered that the Pd metal particles are responsible for the low-temperature activities at >400 K. It is suggested that Cu+chloride species shows the activity only at >570 K.