| Autor: |
Negri C; Department of Chemistry and NIS Centre, University of Turin, Via Giuria 7, Turin, 10125 (I), Italy. elisa.borfecchia@unito.it gloria.berlier@unito.it., Martini A, Deplano G, Lomachenko KA, Janssens TVW, Borfecchia E, Berlier G, Bordiga S |
| Jazyk: |
angličtina |
| Zdroj: |
Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2021 Sep 14; Vol. 23 (34), pp. 18322-18337. Date of Electronic Publication: 2021 Aug 17. |
| DOI: |
10.1039/d1cp01754c |
| Abstrakt: |
The speciation of framework-interacting Cu II sites in Cu-chabazite zeolite catalysts active in the selective catalytic reduction of NO x with NH 3 is studied, to investigate the influence of the Al content on the copper structure and their reactivity towards a NO/O 2 mixture. To this aim, three samples with similar Cu densities and different Si/Al ratios (5, 15 and 29) were studied using in situ X-ray absorption spectroscopy (XAS), FTIR and diffuse reflectance UV-Vis during pretreatment in O 2 followed by the reaction. XAS and UV-Vis data clearly show the main presence of Z 2 Cu II sites (with Z representing a framework negative charge) at a low Si/Al ratio, as predicted. EXAFS wavelet transform analysis showed a non-negligible fraction of proximal Z 2 Cu II monomers, possibly stabilized into two 6-membered rings within the same cage. These sites are not able to form Cu-nitrates by interaction with NO/O 2 . By contrast, framework-anchored Z[Cu II (NO 3 )] complexes with a chelating bidentate structure are formed in samples with a higher Si/Al ratio, by reaction of NO/O 2 with Z[Cu II (OH)] sites or structurally similar mono- or multi-copper Z x [Cu II x O y ] sites. Linear combination fit (LCF) analysis of the XAS data showed good agreement between the fraction of Z[Cu II (OH)]/Z x [Cu II x O y ] sites formed during activation in O 2 and that of Z[Cu II (NO 3 )] complexes formed by reaction with NO/O 2 , further confirming the chemical inertia of Z 2 Cu II towards these reactants in the absence of solvating NH 3 molecules. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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