Structure-reactivity studies of the methane partial oxidation by nitrous oxide-activated iron clusters in various zeolite topologies

Knops-Gerrits, PPHJM
(2003) Symposium on Utilization of Greenhouse Gases held at the 223rd National Meeting of the American-Chemical-Society — Location: ORLANDO(Florida)

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  • Knops-Gerrits, PPHJM
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Abstract
The introduction of iron in the lattice of zeolites with topologies such as CFI, MOR, FER, MFI and CHA, is performed via direct synthesis. Similar materials with high iron loading are made by post-synthetic sublimation of iron by mixing zeolites with Fe-III(acac)(2) and an oxygen calcination procedure. XRD, EXAFS, Mossbauer, DRS, magnetic measurements and EPR resolve and attribute presence of lattice iron and extra-framework clusters. XRD for as made and calcined materials reveals alpha-Fe2O3 particles are absent ( no alpha-Fe2O3 reflection, d(104) = 2.70 Angstrom). From EXAFS structural parameters obtained in the k(3) weighted optimization give 1.7, 2.7 and 3.4Angstrom distances for Fe ((III))-oxygen, Fe((III))- Fe((III)) and Fe ((III))-silicon bonds. In the EPR spectra the ratio of octahedral/tetrahedral iron can be assumed from the presence of lines at g= 2 and 4.3. In mononuclear iron complexes the Fe-O bond distances of 1.86Angstrom (2+, O-h) 6 coordinated and 1.90Angstrom (3+, T-d) 4 coordinated. The bond distances of 1.65 for Si-O and 1.90 A for Fe-O are seen in the direction of the Fe-O-Si bridgeand the Fe-O-Si angles are close to 131.2degrees. Iron oxide clusters in appropriate zeolites realize oxidation of methane into methanol at room temperature after N2O activation. In these experiments we work at 0.1 - 0.5 % level of the adsorption capacity of the zeolite. Fe-5.0-ZSM5 is optimally pretreated in a vacuum at various temperatures around 900degreesC, then the catalyst is allowed to cool and activation with N2O occurs at 250degreesC. The reaction of alpha-oxygen with CH4 occurs at 20degreesC followed by extraction with H2O or D2O.
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Knops-Gerrits, P. (2003). Structure-reactivity studies of the methane partial oxidation by nitrous oxide-activated iron clusters in various zeolite topologies. ACS Symposium Series, 852, 260-279. https://doi.org/10.1021/bk-2003-0852.ch017 (Original work published 2003)