ADDUCT FORMATION AND FURTHER REACTIVITY OF IRON CARBONYL-COMPLEXES INTRODUCED INTO A ZEOLITE MATRIX

Fe(CO)5, Fe2(CO)9 and Fe3(CO)12 have been introduced into a dehydrated HY type zeolite. The iron content in the samples ranged from 1 to 4 wt %. During adsorption the iron complexes retain a molecular structure as shown by IR spectroscopy. For Fe(CO)5 and Fe2(CO)9, a vacuum treatment leads to the evolution of CO and the formation of Fe(CO)4 bonded to the zeolite while in the case of Fe3(CO)12 no CO is evolved. Treating Fe3(CO)12/zeolite under CO atmosphere restores the IR spectra of the Fe(CO)5 or Fe2(CO)9/zeolite system. Thereafter the zeolite acts both as an oxygen-containing ligand leading to L-Fe(CO)4 species and as a Lewis acid able to form adducts with Fe3(CO)12 units via the oxygens of the bridging carbonyls. Heating the loaded zeolite (100-200°C) produces a dehydroxylation of the support which is promoted by the iron carbonyls. The subsequent formation of CO2 and hydrogen is explained by the water-gas shift reaction. Some CO2 remains chemisorbed on the surface as evidenced by the presence of carbonate species. These species can be desorbed by hydrogen treatments with concomitant formation of CH4. Heating up to 250°C leads to total decarbonylation of the iron carbonyl/HY systems and subsequent oxidation of Fe(0) to Fe(II) as evidenced by complexes formed with NO and CO. The oxidation process involves the protons of the zeolite. The Fe2+ ions are mainly located in the supercage in contrast to a conventional Fe2+/Y sample. © 1979, American Chemical Society. All rights reserved.