Structure and electronic state of PdCl2-CuCl2 catalysts supported on activated carbon

The structure and electronic state of PdCl2-CuCl2 catalysts supported on activated carbon (AC) were characterized using XAFS techniques. On the basis of XANES of the Cu K-edge, a majority of CuCl2 supported on the activated carbon was found, to be reduced to Cu+ species, probably by the reduction sites on the support surface. The Cu K-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 Pd K-edge showed the formation of Pd metal particles as weld 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 PdCl2 or CuCl2 on 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. (C) 1996 Academic, Press, Inc.