Active sites in Fe zeolite catalysts for reactions with nitrogen oxides

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The extension project aims at the elucidation of active sites and mechanistic details of important reactions of environmental catalysis catalyzed by Fe zeolites by the application of improved methods of structural analysis for such moieties. We intend to establish the dependence of extinction coefficients of such species in UV-Vis spectroscopy by relating such analyses to parallel field-dependent low-temperature Moessbauer analyses of (57)Fe-ZSM-5 samples, which are available from the previous project or will be freshly prepared. At the same time, we intend to improve assignments in UV-Vis spectra by low-temperature Moessbauer analyses of samples specially prepared to contain disputed signals in high intensities. Identification of catalytically active sites by post-mortem low-temperature Moessbauer analyses of samples with very different activities, which has been commenced in the previous project, will be completed and supported by complementary studies. This effort will be focused on standard SCR, where strong hints on a contribution of small oligomeric Fe(III) oxo cluster are already available. By examining samples with varying ratios between isolated and oligomeric sites, we will also try and establish how the contribution of isolated Fe(III) oxo sites compares with that of the oligomeric sites. To support our conclusion that the active sites of standard SCR atre trivalent in the reaction medium, we will perform kinetic analysis of reoxidation rates of Fe(II) species in relevant situations and compare them with total standard SCR rates. Beyond that, the reason for the drastic increase of NO oxidation activity of freshly prepared Fe zeolitsy by redox activation will be examined. With respect to fast SCR, we inted to support our assignment of activity to Fe(II) sites stabilized by two nearby framework Al sites (Al pairs) by preparing and investigating a series of catalysts containing Fe in ZSM-5 zeolites of different Al distribution in the lattice (and, hence, different abundance of Al pairs).