Copper-containing zeolites are promising catalysts for the reaction of direct oxidation of methane to methanol. In this work, the structure of copper active centers in mordenite-type zeolites prepared by aqueous ion exchange was investigated using X-ray absorption near edge structure XANES and computer modelling. Calculations of theoretical Cu K-XANES spectra were performed for a set of models of active copper centers containing one, two, or three copper atoms. The main problem is the difficulty in defining the local atomic structure of copper centers, which are unevenly distributed in the zeolite framework and largely determine the catalytic properties of the material. In order to describe the experimental Cu K-XANES spectra corresponding to the oxygen activation stage at a temperature of 200°C, it is necessary to take into account the superposition of models of copper and copper oxide centers. The most probable local atomic environment of copper at the considered stage of the catalytic cycle in the studied material was determined. The results obtained are important for establishing the relationship between the structure and catalytic properties of mordenite-type zeolites, as well as for the development of new efficient catalysts.
Ermakova et al. (Wed,) studied this question.