Revisiting the nature of Cu sites in the activated Cu-SSZ-13 catalyst for SCR reaction

E Borfecchia; K A Lomachenko; F Giordanino; H Falsig; P Beato; A V Soldatov; S Bordiga; C Lamberti

doi:10.1039/c4sc02907k

Revisiting the nature of Cu sites in the activated Cu-SSZ-13 catalyst for SCR reaction

Chem Sci. 2015 Jan 1;6(1):548-563. doi: 10.1039/c4sc02907k. Epub 2014 Oct 13.

Authors

E Borfecchia^{1

2}, K A Lomachenko^{1

3}, F Giordanino^{1

2}, H Falsig⁴, P Beato⁴, A V Soldatov³, S Bordiga^{1

2}, C Lamberti^{1

5

3}

Affiliations

¹ Department of Chemistry and INSTM Reference Center , University of Turin , via P. Giuria 7 , 10125 Turin , Italy . Email: carlo.lamberti@unito.it.
² NIS Centre of Excellence , University of Turin , Italy.
³ Southern Federal University , Zorge street 5 , 344090 Rostov-on-Don , Russia.
⁴ Haldor Topsøe A/S , Nymøllevej 55, 2800 Kgs. , Lyngby , Denmark.
⁵ CrisDI Center of Crystallography , University of Turin , Italy.

Abstract

Cu-SSZ-13 is a highly active NH₃-SCR catalyst for the abatement of harmful nitrogen oxides (NO _x , x = 1, 2) from the exhausts of lean-burn engines. The study of Cu-speciation occurring upon thermal dehydration is a key step for the understanding of the enhanced catalytic properties of this material and for identifying the SCR active sites and their redox capability. Herein, we combined FTIR, X-ray absorption (XAS) and emission (XES) spectroscopies with DFT computational analysis to elucidate the nature and location of the most abundant Cu sites in the activated catalyst. Different Cu species have been found to be dominant as a function of the dehydration temperature and conditions. Data analysis revealed that the dehydration process of Cu cations is essentially completed at 250 °C, with the formation of dehydrated [CuOH]⁺ species hosted in close proximity to 1-Al sites in both d6r and 8r units of the SSZ-13 matrix. These species persist at higher temperatures only if a certain amount of O₂ is present in the gas feed, while under inert conditions they undergo virtually total "self-reduction" as a consequence of an OH extra-ligand loss, resulting in bi-coordinated bare Cu⁺ cations. Synchrotron characterization supported by computational analysis allowed an unprecedented quantitative refinement of the local environment and structural parameters of these Cu(ii) and Cu(i) species.