Bimetallic Reforming Catalysts: EXAFS Investigation of the Particle-Growing Process during the Reduction Step
Résumé
EXAFS has been used to study lhe reduction which Ieads to the active species of Pt-Rh and Pt-Re reforming catalysts. The first moments of the formation of the metallic cluster have been followed kimetically at the platinum absorplion edge for two catalysts, Pt-Rh/gAl2O3 and PtRe/g-Al2O3,. using two different modes for the EXAFS setup (different synchrotron stations). The experiments have been made in situ, the sample being under flowing hydrogen at high temperature. The main result is the appearance of long metal-metal distances. of the same range order as that of the bond Iengths existing in the alumina network. They occur solely for a very low number of metal atoms and are probably due lo an intergrowth process with the carrier. The phenomenon seems to be general and disappears with the growth of the particle. © 1990 Academic Press. Inc.