IN-SITU EXAFS STUDIES OF MODIFICATIONS TO SUPPORTED METALLIC CATALYSTS UNDER REACTIVE ATMOSPHERES

Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the structural evolution of monometallic (Pt/Al2O3) and bimetallic (Pt-Re/Al2O3) catalysts with metal loadings representative of those used industrially under conditions close to those seen during preparation (calcination and reduction), during catalysis (under a hydrogen-hydrocarbon mixture), and during regeneration (simulated by cycles of reduction and oxidation). During the catalytic reforming of n-heptane, the formation of bonds to carbon species is observed directly by EXAFS. Despite the fact that only platinum-carbon bonds are observed, bimetallic systems show significant differences compared with monometallic systems with, in the case of Pt-Re, a reduction in the temperature range over which carbon bonding is observed, and structural modifications of the metallic particles. Under the same conditions, no carbon bonding is observed for the Pt-Sn system. In the case of Pt-Sn/Al2O3, the EXAFS results, confirmed by transmission electron microscopy, demonstrate the high resistance to sintering of this bimetallic system compared to the monometallic system.