Abstract: Two kinds of small iron clusters supported on SiO₂-200 (dehydroxylated at 200℃ and SiO₂-600 (de-hydroxylated at 600℃) were prepared by Solvated Metal Atom Impregnation (SMAI) techniques. The iron atom precursor complex, bis (toluene) iron(0) formed in the metal atom reactor, was impregnated into SiO₂ having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by THM, Mosbauer and chemisorption measurements, and the resules show that higher concentration of surface hydroxyl groups of SiO₂-200 favours the formation of more positively charged support iron cluster Fe₂/SiO₂-200 and the lower concentration of surface hydroxyl groups of SiO₂-600 favours the formation of basically neutral supported iron cluster Fe₂/SiO₂-600. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the precursor complex,bis(toluene) fron(0), to decompose more rapidly, and favours the formation of relatively large iron cluster. As a consequence, these two kinds of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fe/SiO₂-200 in F-Treaction is similar to that of the unreduced a-Fe₂O₂, while Fe₂/SiO₂-600 is similar to that of reduced α-Fe₂O₂.

Key words: Iron clusters, Solvated metal atom impregnation. Iron atom precursor complex