Investigating the Low Temperature Formation of Cu II -(N,O) Species on Cu-CHA Zeolites for the Selective Catalytic Reduction of NO x .

Autor: Negri C; Department of Chemistry, INSTM Reference Center and NIS Center, University of Turin, Address Via Giuria 7, I-10135, Turin, Italy., Hammershøi PS; Umicore Denmark ApS, Nøjsomhedsvej 20, 2800, Kgs. Lyngby, Denmark.; Department of Chemical and Biochemical Engineering, Technical University of Denmark, Lyngby, Denmark., Janssens TVW; Umicore Denmark ApS, Nøjsomhedsvej 20, 2800, Kgs. Lyngby, Denmark., Beato P; Haldor Topsøe, Kgs. Lyngby, 2800, Denmark., Berlier G; Department of Chemistry, INSTM Reference Center and NIS Center, University of Turin, Address Via Giuria 7, I-10135, Turin, Italy., Bordiga S; Department of Chemistry, INSTM Reference Center and NIS Center, University of Turin, Address Via Giuria 7, I-10135, Turin, Italy.
Jazyk: angličtina
Zdroj: Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2018 Aug 14; Vol. 24 (46), pp. 12044-12053. Date of Electronic Publication: 2018 Jul 26.
DOI: 10.1002/chem.201802769
Abstrakt: In this work, we show the potentiality of operando FTIR spectroscopy to follow the formation of Cu II -(N,O) species on Cu exchanged chabazite zeolites (Cu-CHA), active for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). In particular, we investigated the reaction of NO and O 2 at low temperature (200 and 50 °C) on a series of Cu-CHA zeolites with different composition (Si/Al and Cu/Al ratios), to investigate the nature of the formed copper nitrates, which have been proposed to be key intermediates in the oxidation part of the SCR cycle. Our results show that chelating bidentate nitrates are the main structures formed at 200 °C. At lower temperature a mixture of chelating and monodentate nitrates are formed, together with the nitrosonium ion NO + , whose amount was found to be proportional to the zeolite Brønsted site concentration. Nitrates were found to mainly form with Cu II ions stabilized by one negative framework charge (Z), Z-[Cu(OH] I or Z-[Cu(O 2 ] I , without involvement of Z 2 -Cu II ones. This evidence, together with the absence of bridging nitrates in samples with high probability for Cu-Cu pairs, indicate that the nitrate ligands are not able to mobilize copper ions, at variance with what recently reported for NH 3 . Finally, water was found to replace preformed chelating copper nitrates and deplete NO + (though with different kinetics) at both temperatures, while favouring the presence of monodentate ones.
(© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)
Databáze: MEDLINE
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