Bimetallic Cu-Fe(II) and Cu-Fe(III) systems supported on mordenite: A spectroscopic insight

Abstract

This paper details the actual composition and some properties of bimetallic Cu-Fe systems deposited on mordenite using sources of iron ions in both oxidation states – Fe²⁺ or Fe³⁺. By methods of Nuclear Magnetic Resonance, UV-Vis, and Mössbauer spectroscopy, details of the reciprocal influence of Cu and Fe ions on the formation of metallic centers/species are revealed, depending on the degree of oxidation of iron ions during simultaneous deposition of a mixture of Cu-Fe ions on mordenite under microwave irradiation. Fundamental differences in the behavior of Fe²⁺ and Fe³⁺ ions are shown. According to the simplest model, ion exchange in zeolites occurs because the role of cations is solely to neutralize the negative charge of the zeolite crystal framework associated with the presence of trivalent Al instead of tetravalent silicon in the tetrahedral environment. The relative decoupling of the cationic group from the zeolite crystal framework allows for its relatively independent modification, creating effective catalytic centers. However, with all the apparent simplicity of this process, a closer examination of the materials obtained through ion exchange process, in many cases allows one to notice certain effects associated with the peculiarities of the chemical properties of each of the elements, their potential interaction with the matrix, and the formation of admixed phases and nanoparticles based on the same elements supported on the zeolite.