2 7 I H I G H L I G H T S 2 0 2 2
CuII progressively develop, supporting the formation of [Cu2(NH3)4O2]2+ complexes , yet with subtle spectral differences for 0.1_5. XANES linear combination fitting (LCF) indicated that the residual [CuI(NH3)2]+ fraction increases as the Si/Al ratio increases, even at constant Cu density, as it is the case for 0.1_5 and 0.6_29. Considering the NOx conversion from fixed-bed tests (Figure 16d), a clear correlation was observed between residual CuI fraction and Turn Over Frequency (TOF) at 200°C.
Extended X-ray absorption fine structure (EXAFS) analysis allowed to correlate the [Cu2(NH3)4O2]2+ local structure with the observed trends in oxidation efficiency. Wavelet Transforms (WT) (Figures 17a and b) were exploited to unambiguously identify Cu-Cu scattering contributions through a characteristic lobe at ca. 7 Å-1 . WT proved the presence of dicopper(II) species in all catalysts after oxidation, while the two local maxima observed along the R direction (LR and HR, Figure 17b) pointed to an EXAFS-
resolvable bimodal distribution of Cu-Cu interatomic distances.
Thanks to a novel machine learning (ML)-assisted EXAFS analysis approach  (Figures 17c,d), a fitting model was implemented, accounting for a minor presence of [CuI(NH3)2]+ and for a bimodal distribution of the Cu-Cu distances in μ-h2,h2-peroxo diamino dicopper(II). The fit confirmed that two distinct coordination motifs are required to fully model the EXAFS of 0.5_15 and 0.6_29, corresponding to different Cu-Cu distance for a bent and planar dicopper(II) complex. The latter component is instead largely dominant in 0.1_5.
This study reveals how the Si/Al ratio of the zeolite host affects the structure of mobile dicopper(II) complexes formed during the oxidation of the [CuI(NH3)2]+ complexes by O2, impacting the oxidation efficiency at a given volumetric Cu density and the NH3-SCR performance at 200°C.
Fig. 17: EXAFS-WT maps after reduction (a) and oxidation (b) steps in the 2 4 Å range. c) Example of ML-assisted EXAFS fitting for 0.5_15, with molecular models of the included structural components and (d) their percentages determined for the three catalysts after the oxidation step.
PRINCIPAL PUBLICATION AND AUTHORS
Assessing the Influence of Zeolite Composition on Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-CHA DeNOx Catalysts by Machine Learning-Assisted X-ray Absorption Spectroscopy, A. Martini (a), C. Negri (a), L. Bugarin (a, b), G. Deplano (a), R.K. Abasabadi (a), K.A. Lomachenko (b), T.V.W. Janssens (c), S. Bordiga (a), G. Berlier (a), E. Borfecchia (a), J. Phys. Chem. Lett., 13, 6164-6170 (2022); https:/doi.org/10.1021/acs.jpclett.2c01107 (a) Department of Chemistry and NIS Centre, University of Turin, Turin (Italy) (b) ESRF (c) Umicore Denmark ApS, Hørsholm (Denmark)
 C. Paolucci et al., Science 357, 898-903 (2017).  C. Negri et al., J. Am. Chem. Soc. 142, 15884-15896 (2021).  A. Martini et al., J. Phys. Chem. A 125, 7080-7091 (2021).