Copper Pairing in the Mordenite Framework as a Function of the Cu^I/Cu^II Speciation

Abstract

Aseries of gas-phase reactants is used to treat aCuexchanged mordenite zeolite with the aim of studying the influence of the reaction environment on the formation of Cu pairs.The rearrangement of Cu ions to form multimeric sites as af unction of their oxidation state was probed by X-ray absorption spectroscopy( XAS) and also by applying advanced analysis through wavelet transform, am ethod able to specifically locate Cu-Cu interactions also in the presence of overlapping contributions from other scattering paths.T he nature of the Cu-oxo species formed upon oxidation was further crosschecked by DFT-assisted fitting of the EXAFS data and by resonant Raman spectroscopy. Altogether,the Cu I / Cu II speciation clearly correlates with Cu proximity, with metal ion pairs quantitatively forming under an oxidative environment.

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“…S 0 2 factor was fixed to 1 for all the paths, on the basis of the EXAFS fit performed for the CoO reference (Hursán et al, 2023). In order to reduce the correlation between the coordination numbers and the Debye-Waller (DW) factors, the DW for the Co-Co path, was set to 0.008 Å 2 , a value already used for dispersed Cu sites in zeolites frameworks (Martini, Signorile, et al, 2020;Deplano et al, 2021;Martini et al, 2017). At the same time, it has been assumed that the N and C have the same DWs.…”