A. Bensaddik et al., IN-SITU STUDY BY XAS OF THE SULFIDATION OF INDUSTRIAL CATALYSTS - THEPT AND PTRE AL2O3 SYSTEMS/, Applied catalysis. A, General, 162(1-2), 1997, pp. 171-180
Extended X-ray absorption fine structure (EXAFS) spectroscopy has been
used to follow the structural evolution of the monometallic Pt/Al2O3
and the bimetallic Pt-Re/Al2O3 systems during reduction and sulfidatio
n treatments. After sulfidation a second reduction has been performed
in order to study the elimination of reversibly adsorbed sulfur. For t
he monometallic system, starting from the reduced state, the number of
platinum-platinum bonds decreases significantly from 4.5 to 1.5 after
sulfidation and a second reduction. In addition, a significant amount
of sulfur is measured around platinum atoms (3 sulfur atoms per plati
num atom). On the contrary, for the bimetallic platinum-rhenium system
, the number of sulfur atoms in the vicinity of platinum atoms is smal
ler (1 sulfur atom per platinum atom) with no major change for the num
ber of platinum-platinum bonds. Simultaneous measurements at the rheni
um absorption edge show that the sulfur atoms are preferentially fixed
by the rhenium atoms (2 sulfur atoms per rhenium atom). From these qu
antitative results, a structural model for both the monometallic and t
he bimetallic systems is proposed to describe the different behaviors.
(C) 1997 Elsevier Science B.V.