Active sites in Fe zeolite catalysts for reactions with nitrogen oxides

扩展项目旨在应用改进的铁分子筛结构分析方法，阐明铁分子筛催化环境催化重要反应的活性位点和机理细节。我们打算通过将这些分析与（57）Fe-ZSM-5样品的平行场依赖低温Moessbauer分析联系起来，建立这些物种在UV-Vis光谱中的消光系数的依赖性，这些样品可从先前的项目中获得或将新鲜制备。同时，我们打算通过低温Moessbauer分析来改善紫外-可见光谱的分配，这些样品是专门为含有高强度有争议的信号而制备的。通过对具有不同活性的样品进行死后低温Moessbauer分析来鉴定催化活性位点，这在上一个项目中已经开始，将通过补充研究来完成和支持。这项工作将集中在标准SCR上，其中已经有关于小的低聚铁（III）氧簇贡献的强烈暗示。通过检测分离位点和低聚位点之间不同比例的样品，我们还将尝试确定分离的Fe（III）氧位点与低聚位点的贡献如何比较。为了支持我们的结论，即标准SCR的活性位点在反应介质中是三价的，我们将对相关情况下Fe（II）物种的再氧化速率进行动力学分析，并将其与总标准SCR速率进行比较。除此之外，本文还将探讨新制备的铁沸石经氧化还原活化后NO氧化活性急剧提高的原因。在快速SCR方面，我们通过制备和研究一系列含有Fe的催化剂，在晶格中具有不同Al分布（因此具有不同丰度的Al对）的ZSM-5沸石中制备和研究了由两个附近的框架Al位点（Al对）稳定的Fe（II）位点。

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).