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 durin g preparation (calcination and reduction), during catalysis (under a h ydrogen-hydrocarbon mixture), and during regeneration (simulated by cy cles 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 observ ed, bimetallic systems show significant differences compared with mono metallic systems with, in the case of Pt-Re, a reduction in the temper ature range over which carbon bonding is observed, and structural modi fications of the metallic particles. Under the same conditions, no car bon bonding is observed for the Pt-Sn system. In the case of Pt-Sn/Al2 O3, the EXAFS results, confirmed by transmission electron microscopy, demonstrate the high resistance to sintering of this bimetallic system compared to the monometallic system.