TM oxo-cluster

Figure 31.4 Schematic representation of the (a) charge transfer and (b) hydrogen-bonding interactions between hydrophilic PEO groups of surfactants and TM oxo-clusters.

The catalytic decomposition of N20 is regulated by the cycle Fc"/Fcm. N20 interacts with reduced Fe[[ site (Eq.16.1) to yield an extra-lattice oxygen Fe[[[-0 species, the so-called a-oxygen by Panov et al. (29). Most of studies have concluded that the removal of a-oxygen (Eq. 16.2) exhibits the lowest rate constant. The remarkable behavior of Fe exchanged in some zeolites could be ascribed to the occurrence of easily reduced and completely reversible Fe oxo-cation sites (28). TPR experiments by H2 and CO of N20-treated Fe-MFI (27) and Fe-BEA (33) have shown that such Fem-0 sites are much more reductible than those formed by 02 treatment. The influence of the zeolite on the reductibility of Fe species could be understand from quantum chemical calculations (DFT method) on model clusters of FAU and BEA containing Cu", Co" and Fe" cations (36). The calculations indicate that a charge transfer from zeolite to TM ion occurs of ca. one electron, and that the TM-zeolite system behaves like a supermolecule. Obviously, the addition of a reductant such as hydrocarbons (25, 26, 37, 38), CO (39, 40) or NH3 (41) boosts the N20 decomposition by a faster reduction of Fem-0 species. 

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