Methane partial oxidation in iron zeolites: theory versus experiment

The conversion of methane to methanol over zeolitic cr-oxygen sites has been demonstrated using Fe-ZSM-5. To discriminate between mono- and poly-nuclear active sites, we prepared the [Fe]-ZEO with iron in the ZEOlite lattice via direct synthesis and Fe, -ZEO, by dispersion of x wt.% iron on the ZEOlite. Shape-selective formation of nano-clusters of iron oxides with various sizes is realized inside the pore-sizes varying from 10.0 to 8.0 and 6.3 to 4.3 Angstrom of the CFI, MOR, MFI, and CHA zeolites. The Fe-K edge X-ray absorption data were obtained for the Fe-CIT-5, Fe-ZSM-5, Fe-MOR and Fe-CHA zeolites containing iron clusters. In Mossbauer spectroscopy the absence and presence of a hyperfine magnetic field (HMF) for [Fe]-CIT-5 and Fe-CIT-5 are seen. The quantum mechanics calculations analyze the different environments of iron, e,g, the tetrahedral lattice occluded species, the di-nuclear sites attached to the zeolite, the nano-phase hematite sites. The molecular mechanics calculations involve a new molecular mechanics force field, the universal force field (UFF). alpha -Oxygen can be formed on di-nuclear iron rites in zeolites by N2O decomposition at elevated temperatures and is dependent on the zeolite structure utilized. Fe-chabazite (CHA), Fe-mordenite (MOR) and Fe-CIT-5 (CFI) were found to be less active than Fe-ZSM-5. A range of preparative and activation conditions were studied preceding methane conversion. Proper activation is essential to maximize catalyst actvity, e.g. pretreatment under vacuum at 800-900 degreesC, activation with N2O at 250 degreesC and reaction with methane at 20 degreesC, Extraction of methanol from the catalyst is performed with H2O Structure-activity effects are discussed. (C) 2001 Elsevier Science B.V, All rights reserved

Reactivity of methane mono-oxygenase, insights from quantum mechanic studies on synthetic iron model complexes

Methane mono-oxygenase (MMO) and deoxyhemerythrin (DHr) are examples of di-iron enzymes that catalyze the dissociative and non-dissociative binding of molecular oxygen. To mimic the MMO active site with a finite cluster, we chose to study the binuclear heptapodate coordinated iron(III)-complexes of N,N,N,N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diamino-propane (HPTB) and N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diamino-propane (HPTP). These have active sites of the form [Fez (HPTP)(mu -OH)](4+) (1) and [Fe-2(HPTB)(mu -OH)](4+) (1) and [Fe-2(HPTB)(mu -OH)(4+) (2). Quantum mechanics structures are compared with the experimental data obtained from the EXAFS analysis. For the O-2 binding on the reduced active site. the mu-eta (1):eta (1)-O-2 mode seems the slightly more stable precursor to the O=Fe-O-Fe=O bis-ferryl (re)active site. The nature of the ferryl groups are these of a reactive two center three electron bond. (C) 2001 Elsevier Science B.V. All rights reserved

Carbon monoxide electrooxidation on Pt and PtRu modified zeolite X

Zeolite NaX was modified by Pt and Pt/Ru nanodispersed metallic clusters. This modification was achieved by zeolite impregnation with acetylacetonate salt/acetone solution, followed by acetone evaporation and thermal decomposition of organometallic complex. Samples characterization was performed by X-ray diffraction analysis, nitrogen adsorption-desorption measurements and Raman spectroscopy. The incorporation of metal into zeolite cavities induced the amorphisation of the zeolite framework on the local level. The mixture of modified zeolite and 10 wt% of carbon black, in a form of thin layer, was pasted to a glassy carbon surface by Nafion. Electrocatalytic properties of metal-modified zeolites were tested in CO electrooxidation reaction. The mutual influence between Pt and Ru atoms enhanced electroactivity of Pt/Ru-modified zeolite toward carbon monoxide electrooxidation. The behavior of untreated 13X zeolite was investigated under the same condition in order to asses the influence of the support. Gradual deactivation of 13X electrode occurred