Ammonia-Containing Species Formed in Cu-Chabazite As Per In SituEPR, Solid-State NMR, and DFT Calculations

Nowadays, the most attractive technology for the elimination of nitric oxides from the exhaust gas of diesel vehicles is the selective catalytic reduction with ammonia (NH3-SCR-NOx) using Cu zeolite with the chabazite structure as the catalyst. Isolated copper species are the active sites, but the reaction intermediates and the overall reaction mechanism are still under debate. Here, we study the interaction of ammonia with zeolite Cu-SSZ-13 (CHA topology) with a uniform distribution of Cu2+ sites prepared in one pot and a conventional Cu-ZSM-5 (MFI topology) for comparison. In situ EPR and solid-state NMR spectroscopies combined with DFT calculations have allowed the identification of NH4+, [Cu(NH3)5]2+, [Cu(Of)2(NH3)2]2+, [Cu(Of)3NH3]2+, [Cu(NH3)2]+, and [CuOf(NH3)]+ (Of being framework oxygen) under different conditions. The results demonstrate that ammonia is able to reduce Cu2+ to Cu+ and provide new information on the species formed in Cu-SSZ-13, which have important implications for the elucidation of the SCR reaction mechanism.The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the Severo Ochoa program (SEV-2012-0267) and operating grants Consolider Ingenio Multicat CSD-2009-00050, MAT-2012-3856-C02-01, as well as Generalitat Valenciana through the PROMETEOII/2013/011 Project. Red Espanola de Super-computacion (RES) and Centre de Calcul de la Universitat de Valencia are gratefully acknowledged for computational facilities and technical assistance. M.M. and B.H. thank ITQ for grants.Moreno González, M.; Hueso Fuentes, B.; Boronat Zaragoza, M.; Blasco Lanzuela, T.; Corma Canós, A. (2015). Ammonia-Containing Species Formed in Cu-Chabazite As Per In SituEPR, Solid-State NMR, and DFT Calculations. Journal of Physical Chemistry Letters. 6(6):1011-1017. doi:10.1021/acs.jpclett.5b00069S101110176