Wavelet analysis of a Cu-oxo zeolite EXAFS simulated spectrum

Structure of copper sites in zeolites examined by Fourier and wavelet transform analysis of EXAFS

“…12,14,24,32,33 Previous investigations of theoretically modeled EXAFS spectra showed the principal possibility to resolve Cu-Cu scattering pathways in the second coordination shell using WT. 44,48 In this respect, our wavelet analysis provides unambiguous evidence, which enables the discrimination of the different scatters contributing to the peak at about 2.3Å in FT EXAFS. The presence of two separate lobes at about (7.0Å À1 ; 2.4Å) and (11.0Å À1 ; 2.5Å) in WT EXAFS for Cu(3.4)MOR (10) and Cu(4.0)MFI (12) indicates the existence of both Cu-Al/Si and Table 2 Best-fit parameters optimized by EXAFS fits of the k 3 -weighted spectrum of activated copper-exchanged zeolites of different topologies employing two DFT-optimized geometries for dicopper mono-m-oxo sites and copper clusters as the starting guess.…”

“…Wavelet transform (WT) analysis is a powerful technique, coming from the signal processing eld, which has attracted signicant attention in the eld of X-ray absorption spectroscopy. [44][45][46][47][48] This is due to the possibility that arises from this approach to resolve overlapping contributions coming from different neighbor atoms. If two or more groups of different atoms are localized at close distances around the absorbing atom, their contributions in the direct R space overlap, making the classical FT analysis of the EXAFS spectrum rather challenging.…”

“…We employed a Morlet wavelet mother function for the WT transform of all spectra within the k-range of 1-16Å À1 . 48 The selection of this wavelet was governed by the fast oscillatory part localized in a Gaussian envelope, making its real and imaginary parts similar to an EXAFS spectrum. Continuous wavelet transform was carried out for 128 data points using a built-in function in Mathematica soware, 50 with subsequent visualization as 2D counterplot projection of a 3D graph.…”

Structure and Reactivity of Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-Ion-Exchanged Chabazite Catalyst for NH3-Mediated Selective Catalytic Reduction

“…It is clear that signals produced by heavier atoms, such as Cu, are localized at higher k values with respect to lighter atoms. On this background, a WT analysis allows for a better discrimination of the nature of the scattering contributions around the absorber, compared to the classical FT analysis. ,− The WT analysis results in a 2D representation of the EXAFS, simultaneously revealing the signal features in both R - and k -space. Then, one can visually resolve the scattering contributions originating from atomic neighbors having enough Z -contrast in their F ( k ) functions.…”

Activity Descriptors Derived from Comparison of Mo and Fe as Active Metal for Methane Conversion to Aromatics

“…Multivariate curve resolution (MCR) analysis is used for decomposition of the measured X-ray absorption near edge spectra (XANES), that represent an average over all absorbing atoms, into the individual spectra of the different phases present. [44][45][46] Herewith, the fractional contribution of each phase can be determined. This paper aims at understanding the differences in activity of Mo/HZSM-5 and Fe/HZSM-5 building on previous results obtained for Mo/HZSM-5.…”