CATALYTIC AND STRUCTURAL-PROPERTIES OF RUTHENIUM MONOMETALLIC AND BIMETALLIC CATALYSTS - CHARACTERIZATION BY EXAFS AND XRD

This work presents an extensive structural study of Ru monometallic (R u/Al2O3) and bimetallic (RuM/Al2O3, M = Ge, Sn, Pb) catalysts by means of extended X-ray absorption fine structure (EXAFS) at the Ru K-edge, and X-ray powder diffraction. Samples prepared by the controlled surf ace reaction (CSR) technique and by the classical impregnation method with different Ru loadings and different Ru/M weight ratios were studi ed. The results show that monometallic catalysts contain small Ru clus ters whose degree of dispersion, measured from the average Ru coordina tion numbers, decreases with the Ru loading. The clusters are formed b y metallic ruthenium. The Ru 1% weight sample, prepared by the control led surface reaction technique, is the most highly dispersed, comprisi ng small clusters of no more than 12 atoms. The samples prepared by th is latter technique are in general better dispersed than those prepare d by the impregnation method, Addition of germanium produces an increa se of Ru dispersion, and in the case of the highest Ge/Ru ratio, bimet allic clusters formed. The degree of dispersion is higher in some Sn-c ontaining catalysts while lead does not induce any structural change.