Characterization of silica-supported bimetallic iron-nickel catalysts by EXAFS

FeNi/SiO₂ bimetallic catalysts with varying composition were prepared according to two procedures: alkoxide and impregnation methods. The size distribution of the metal clusters and the local structure around each kind of metal atom in the clusters are studied by TEM, XRD, and EXAFS. Fe and Ni atoms are concluded to be in small clusters with a fcc structure; that is, alloy is formed. The metal particles are not, however, uniform in composition and consist of an Ni-rich kernel covered with outer layers which contain more Fe. This tendency is more pronounced in the catalyst prepared by the alkoxide method. The reason for the evolution of such inhomogeneous clusters is examined by EXAFS through the local structure change during the preparation procedure.