Construction of highly dispersed mononuclear iron-oxo species in the supercages of Y zeolite by use of surface organometallic chemistry

Y zeolite containing well-dispersed iron (Fe/Y–G) was prepared by grafting reaction of the ferrocene molecule (Cp2Fe) on the acidic sites of HY zeolite followed by thermal treatment in oxygen. In situ FTIR and chemical analysis revealed that Cp2Fe molecule adsorbed on the zeolite surface lost one cyclopentadienyl group leading under vacuum at 423 K to the formation of a surface iron-cyclopentadienyl complex. Fe/Y–G was then obtained by calcination at 773 K in flowing oxygen. This solid was characterized by XPS, XAFS, CO adsorption FTIR, UV–vis DRS, and catalytic oxidation reaction of CO with oxygen. The characteristic oxygen-to-metal charge-transfer transition bands at ca. 215 nm and 250 nm showed existence of Fe3+ of Fe/Y–G in isolated tetrahedral sites. Both the 2P3/2 and 2P1/2 electron binding energies of iron and the Fe K edge energy were higher than those of Fe2O3, suggesting that the iron ions contained in Fe/Y–G were highly dispersed and had higher spin-orbital splitting, due to the hybridization of iron 4p atomic orbitals with partly 3d molecular orbitals. The Fe/Y–G showed only one ν(CO) infrared adsorption band at 2194 cm−1, very different from a Fe/Y–I sample prepared by impregnation with FeCl3. The Fe/Y–G zeolite showed a higher catalytic activity in the oxidation of carbon monoxide with molecular oxygen than the Fe/Y–I sample. This behavior was ascribed to the special coordination geometry and electronic structure of the iron atom in the zeolite.