Pecularities of XANES Simulations for Cu(II) Sites in Square-Planar Coordination in Cu-Exchanged Zeolites

Understanding the relationship between the active sites structure of the catalysts based on Cu-exchange zeolites and their productivity is an important step towards obtaining catalysts with optimized properties. One of the main experimental techniques employed for characterization of metal sites in Cu-exchanged zeolites is XANES spectroscopy, which provides information on changes in the charge and structure of catalyst's active sites during activation and under reaction conditions. The peculiarities of XANES simulations for model Cu(II) sites in the square-planar coordination are considered. It is shown that, in order to reproduce the shape of the experimental curves, it is important to take into account the contributions of two competitive adsorption channels due to so-called "shake-down" effects, in which Cu ions have the 3d(10)L and 3d(9) electron configurations in the excited state. This method allows obtaining the most representative XANES spectra and can be used to analyze the structure of copper centers in Cu-exchange zeolites of various topologies.