Carbon-supported palladiunçm catalysts for liquid-phase hydrodechlorination of carbon tetrachloride to chloroform

L.M. GÓMEZ-SAINERO; J.M. GRAU; A. ARCOYA ; X.L. SEOANE

STUDIES IN SURFACE SCIENCE AND CATALYSIS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2000 vol. 130 p. 2009 - 2014

0039-3037

Several catalysts containing 1 wt% Pd on carbon were prepared by incipient wetness impregnation of the support with H2PdCl4 (CPd series) or Pd(NO3)2 (NPd series) aqueous solutions. Catalysts of the CPd series were reduced at 393, 523, 623 and 723 K, whereas two NPd samples (one calcined and the other uncalcined) were reduced at 523 K. The TPR results indicate that reduction of Pd precursor in CPd is more difficult than in NPd samples, which are reduced at sub-ambient temperature. As shown by CO chemisorption, metal dispersion in NPd is lower than in CPd catalysts, in which dispersion decreases as the reduction temperature increases. Analysis by XPS shows that Pd0 and Pdn+ species are present on the catalysts surface and that their proportion depends on the reduction temperature and the nature of the palladium precursor. All the catalysts were active in the hydrodechlorination of carbon tetrachloride to chloroform, the CPd samples being mare selective than the NPd ones. The activity is related to the Pdn+/Pd0 ratio, and a maximum was found for the value  1. The results are explained assuming that the active site is dual in nature [Pdn+-Pd0]. Carbon tetrachloride is adsorbed and activated on Pdn+ and H2 is adsorbed and dissociated on Pd0.Iteraction between these two adsorbed species gives CHCl3 and HCl.