EXAFS STUDY OF MONOMETALLIC AND BIMETALLIC RUTHENIUM BASED CATALYSTS - GE K-EDGE ENVIRONMENT IN RUGE AL2O3 AND STRUCTURAL EFFECTS OF CO ADSORPTION/

We report on the study of the structural modifications induced in Ru/A l2O3 catalysts by Ge addition and on the changes in the Ru environment upon CO adsorption in monometallic (Ru/Al2O3) and bimetallic (RuMe/Al 2O3, Me = Ge, Sn, Pb) samples. Extended X-ray absorption fine structur e measurements were performed at the Ge and Ru K-edges, Samples prepar ed by the controlled surface reaction (CSR) technique and by the class ical impregnation method with different Ru loadings and different Ru/M e weight ratios were studied, The results show that germanium is prese nt as oxide even after reduction at high temperatures, Germanium modif ies the catalysts in two ways, (i) inducing a greater dispersion of th e catalysts and (ii) covering the surface of the ruthenium particles a s germanium oxide. The interplay of this two effects can explain the d ifferences in the catalytic properties, The EXAFS study of the catalys t after CO adsorption shows that the Ru-delta+ oxide species disappear from the surface of the metallic ruthenium particles explaining why C O adsorption is higher than H-2 adsorption.