Abatement of harmful emissions from incineration processes is especially important in highly populated areas. This results in tight legislation on the emission of NOx from both mobile and stationary sources.  Copper substituted zeolites are active catalysts in the NH3-SCR reaction with high selectivity towards N2. Among them especially the small-pore zeolite chabazite is under investigation due to the high hydrothermal stability.  In a fresh catalyst in equilibrium with the atmosphere the copper centers are fully oxidized and fully hydrated copper(II) ions with a high degree of freedom in the zeolite structure. During heating to the operation temperature above 350 degres the zeolite materials go through dehydration and the nature of the copper sites change gradually. The catalytically active sites are generated in-situ based upon the internal structure of the zeolite material and the dehydration conditions.  Electron Paramagnetic Resonance (EPR) spectroscopy is sensitive to the dynamics, the geometry and the coordination number of the paramagnetic copper(II) sites and can be applied both ex- and in situ.  In this work we will present the results of an EPR spectroscopic investigation of the copper sites in different zeolites and correlate the results with evidence from other characterization methods and activity measurements. By using the same activation protocol and the same aluminum and copper content the investigation reveals fundamental differences in the copper coordination patterns present depending on the structure of the zeolite material: The spectroscopic signature of some of the copper sites generated by gentle dehydration in copper substituted chabazite (SSZ-13) persists to high temperatures whereas the signature of the copper species generated by the same gentle treatment in copper substituted ZSM-5 and Beta disappear and are replaced by new features at high activation temperatures.

EPR studies of copper substituted zeolites: In situ generation of active sites for NH3-SCR deNOx catalysts by dehydration

247th National Meeting (2014)

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