PREPARATION OF SUPPORTED IRON CLUSTERS AND THEIR MÖSSBAUER EFFECT SPECTRA

Overview & Synopsis

A new method for the preparation of iron clusters on porous materials was developed. An aqueous ferric nitrate solution in the micropores of alumina was hydrolized with ammonium hydroxide to deposit ferric hydroxide on the wall of micropores. Then the precursor was reduced at 450 - 500°C with hydrogen to convert about half of the iron complex into metallic iron. The average size of the metallic iron clusters was determined from the amount of chemisorbed CO to be about 1 nm. Mössbauer effect spectra of reduced samples were composed of the six magnetically split peaks of metallic iron, a single peak of superparamagnetic iron metal and a ferrous doublet. The fractions of metallic iron in the reduced samples was determined from the spectra were and with that determined by dioxygen adsorption. The fraction of superparamagnetic iron metal in the total metallic iron was about 30% at room temperature, confirming that metallic particles were quite small.