EXAFS wavelet transform analysis of Cu-MOR zeolites for the direct methane to methanol conversion

Abstract

An innovative approach in EXAFS analysis and fitting using wavelet transforms reveals local structure and nuclearity of Cu-species in zeolites.

Investigating the role of Cu-oxo species in Cu-nitrate formation over Cu-CHA catalysts

“…An intense peak located around k = 5.5–6.5 Å -1 and R = 2.5 Å is related to Si and Al framework atoms 16 that cannot be discriminated through the WT analysis due to similar atomic numbers. 65 At R values higher than 2.5 Å, the second lobe ridge extends within 7 and 8 Å −1 , confirming the existence of a Cu–Cu ef path as indicated by the FT-EXAFS fits reported in Section 3.2.1.…”

Identification of Kinetic and Spectroscopic Signatures of Copper Sites for Direct Oxidation of Methane to Methanol

“…[40][41][42]51,65] Thes econd peak comprises the superposition of contributions from aluminum and silicon of the zeolite framework (denoted as "A l/Si") and copper scatterers of extra-framework species,which comprise two and more copper atoms. [51,66] Fitting of the EXAFS spectra yields similar values for the Cu-O,Cu-Al/ Si and Cu-Cu distances in all oxygen-activated CuMOR samples (Table 2; Supporting Information, Figures S3-S10). Thef itted coordination numbers (CN) for copperoxygen, copper-Al/Si and coppercopper contribution in Cu-(4.3)MOR correspond to 4.0, 2.0 and 0.3, respectively,a nd change insignificantly when varying the copper loading.…”

Identification of Kinetic and Spectroscopic Signatures of Copper Sites for Direct Oxidation of Methane to Methanol

“…The first coordination sphere originates from oxygen atoms surrounding copper [40–42, 51, 65] . The second peak comprises the superposition of contributions from aluminum and silicon of the zeolite framework (denoted as “Al/Si”) and copper scatterers of extra‐framework species, which comprise two and more copper atoms [51, 66] . Fitting of the EXAFS spectra yields similar values for the Cu‐O, Cu‐Al/Si and Cu‐Cu distances in all oxygen‐activated CuMOR samples (Table 2; Supporting Information, Figures S3–S10).…”

“…[40][41][42]51,65] Thes econd peak comprises the superposition of contributions from aluminum and silicon of the zeolite framework (denoted as "Al/Si") and copper scatterers of extra-framework species,which comprise two and more copper atoms. [51,66] Fitting of the EXAFS spectra yields similar values for the Cu-O,Cu-Al/ Si and Cu-Cu distances in all oxygen-activated CuMOR samples ( copper loading. TheC u-Cu coordination number suggests that the copper oligomeric species are diluted with copper monomers,l eading to averaged Cu-Cu CN lower than unity.…”