EXAFS determination of the size of Co clusters on silica

The metallic Co catalyst for the Fischer-Tropsch reaction is prepared by reduction of Co salts impregnating microporous silica. The average size of the metallic Co clusters is determined from the average number of neighbours deduced from Co K-edge EXAFS of catalyst samples. A model EXAFS signal constructed from the scattering paths of Co metal fcc lattice with lengths up to 5 Å is calibrated on a reference spectrum of Co metal foil. Catalyst spectra are interpreted with the same model expanded with variable neighbour fractions of the four nearest shells. Cluster size is obtained from comparison with the neighbour fractions of consecutive fcc magic-number clusters.