Preparation of Nano-Sized γ-Al 2O 3 Supported Iron Catalyst for Fischer-Tropsch Synthesis by Solvated Metal Atom Impregnation Methods

Abstract

Two types of small iron clusters supported on γ-Al 2O 3-RT(dehydroxylated at room temperature) and γ-Al 2O 3-800 (dehydroxylated at 800 °C) 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 γ-Al 2O 3 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 TEM, Mossbauer, and chemisorption measurements, and the results show that higher concentration of surface hydroxyl groups of γ-Al 2O 3-RT favors the formation of more positively charged supported iron cluster Fe n /γ-Al 2O 3-RT, and the lower concentration of surface hydroxyl groups of γ-Al 2O 3-800 favors the formation of basically neutral supported iron cluster Fe n /γ-Al 2O 3-800. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the rapid decomposition of precursor complex, bis(toluene)iron(0), and favors the formation of relatively large iron cluster. Consequently, these two types of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fe n /γ-Al 2O 3-RT in F-T reaction is similar to that of the unreduced α-Fe 2O 3 and that of Fe n /γ-Al 2O 3-800 is similar to that of the reduced α-Fe 2O 3.