EXAFS determination of the size of Co clusters on silica

The metallic Co catalyst for the Fischer-Tropsch reaction is prepared by re duction of Co salts impregnating microporous silica. The average size of th e metallic Co clusters is determined from the average number of neighbours deduced from Co K-edge EXAFS of catalyst samples. A model EXAFS signal cons tructed from the scattering paths of Co metal fcc lattice with lengths up t o 5 Angstrom is calibrated on a reference spectrum of Co metal foil. Cataly st spectra are interpreted with the same model expanded with variable neigh bour fractions of the four nearest shells. Cluster size is obtained from co mparison with the neighbour fractions of consecutive fcc magic-number clust ers.