| Autor: |
Negri C; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy., Selleri T; Dipartimento di Energia, Laboratorio di Catalisi e Processi Catalitici, Politecnico di Milano, Via La Masa 34, I-20156 Milano, Italy., Borfecchia E; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy., Martini A; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy.; Smart Materials Research Institute, Southern Federal University, Sladkova Street 174/28, 344090 Rostov-on-Don, Russia., Lomachenko KA; European Synchrotron Radiation Facility, 71 Avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France., Janssens TVW; Umicore Denmark ApS, Kogle Allé 1, 2970 Hørsholm, Denmark., Cutini M; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy., Bordiga S; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy., Berlier G; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, I-10125 Turin, Italy. |
| Abstrakt: |
The NH 3 -mediated selective catalytic reduction (NH 3 -SCR) of NOx over Cu-ion-exchanged chabazite (Cu-CHA) catalysts is the basis of the technology for abatement of NOx from diesel vehicles. A crucial step in this reaction is the activation of oxygen. Under conditions for low-temperature NH 3 -SCR, oxygen only reacts with Cu I ions, which are present as mobile Cu I diamine complexes [Cu I (NH 3 ) 2 ] + . To determine the structure and reactivity of the species formed by oxidation of these Cu I diamine complexes with oxygen at 200 °C, we have followed this reaction, using a Cu-CHA catalyst with a Si/Al ratio of 15 and 2.6 wt% Cu, by X-ray absorption spectroscopies (XANES and EXAFS) and diffuse reflectance UV-Vis spectroscopy, with the support of DFT calculations and advanced EXAFS wavelet transform analysis. The results provide unprecedented direct evidence for the formation of a [Cu 2 (NH 3 ) 4 O 2 ] 2+ mobile complex with a side-on μ-η 2 ,η 2 -peroxo diamino dicopper(II) structure, accounting for 80-90% of the total Cu content. These [Cu 2 (NH 3 ) 4 O 2 ] 2+ are completely reduced to [Cu I (NH 3 ) 2 ] + at 200 °C in a mixture of NO and NH 3 . Some N 2 is formed as well, which suggests the role of the dimeric complexes in the low-temperature NH 3 -SCR reaction. The reaction of [Cu 2 (NH 3 ) 4 O 2 ] 2+ complexes with NH 3 leads to a partial reduction of the Cu without any formation of N 2 . The reaction with NO results in an almost complete reduction to Cu I , under the formation of N 2 . This indicates that the low-temperature NH 3 -SCR reaction proceeds via a reaction of these complexes with NO. |
