Cu-zeolites are very efficient catalyts for the selective reduction of nitrogen oxides using ammonia (NH3-SCR-NOx) or hydrocarbon (HC-SCR-NOx) as reducing agents.1 It is generally assumed that the active sites for NH3-SCR-NOx are isolated Cu2+ cations,2 whereas more controversy exists on those working for HC-SCR-NOx.1Also the reaction mechanism is still under debate because of the high complexity of these two catalytic systems.Here, we compare the interaction of ammonia and propane with medium pore Cu-ZSM-5 and Cu-TNU-9 zeolites, and with large pore zeolite CuY, with similar chemical composition (Si/Al=11-13; 90-130 % Cu2+ exchange) using in situ EPR and NMR spectroscopies and DFT theoretical calculations. EPR allows the detection of isolated Cu2+sites and their interaction with adsorbed molecules, while NMR allows the direct observation of the adsorbate, thus providing complementary information.NMR and EPR spectra reveal that there is a weak but significant interaction of propane with Cu2+ sites in Cu-zeolites active for HC-SCR-NOx reaction, while ammonia is able to coordinate isolated Cu2+. The adsorption of NH3 and 15N-enriched 15NH3 on Cu-zeolites at room temperature and the subsequent heating at increasing temperatures has allowed the identification of three [Cu(NH3)x]2+ complexes with varying stability by EPR. Similar experiments were carried out using 15NH3 to record the 15N MAS NMR spectra, and have shown the formation of NH4+ on Br�nsted acid sites, and the appearence of two new signals of [Cu(NH3)x]+ complexes, more stable than [Cu(NH3)x]2+. The nature of the complexes formed is discussed on the basis of DFT calculations.References1. U. Deka, I. Lezcano-Gonzalez, B. M. Weckhuisen, A. M. Beale, ACS Catal. 2013 , 3,4132. B. Moden, J. M. Donohye, W. E. Cormier and H-X. Li. Topics Catal. 2010  , 53, 1367.

Interaction of reducing agents with Cu-zeolite catalysts for the selective reduction of nitrogen oxide

248th National Meeting (2014)

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