Copper pairing in the mordenite framework as a function of the Cu(I)/Cu(II) speciation

Gabriele Deplano, Andrea Martini, Matteo Signorile, Elisa Borfecchia, Valentina Crocellà, Stian Svelle and Silvia Bordiga.

A series of gas-phase reactants is used to treat a Cu-exchanged 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 a function of their oxidation state was probed by X-ray Absorption Spectroscopy (XAS), also by applying advanced analysis through Wavelet Transform, a method able to specifically locate Cu-Cu interactions also in the presence of overlapping contributions from other scattering paths. The 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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