IN-SITU STUDY BY XAS OF THE SULFIDATION OF INDUSTRIAL CATALYSTS - THEPT AND PTRE AL2O3 SYSTEMS/

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.