ІЧ-СПЕКТРОСКОПІЧНИЙ АНАЛІЗ СКЛАДНИХ ОКСИДНИХ КАТАЛІЗАТОРІВ ТИПУ хCrРО4уNi3(РО4)2

Анотація

The results of the IR spectroscopic method for the analysis of synthesized individual chromium and nickel phosphates and binary complex catalytic systems of the type xСrPO₄´yNi₃(PO₄)₂ on their basis made it possible to identify the composition of catalysts and to identify a number of features and patterns. It is established that the studied air-dry orthophosphates in the process of synthesis from solutions crystallize in the form of hydrates. In this case, the water molecules that are part of the crystalline hydrates are not neutral structural elements in the lattice of hydrate, but participate in various interactions with cationic and anionic salt sublattices. The state of water in crystalline hydrates and the method of placement and the nature of the connection of its molecules with other elements of the crystalline lattices significantly influences the process of thermal hydration of formed compounds. It was established that in the process of thermal processing of synthesized complex chromium-nickel-phosphate systems there is a gradual decrease in the intensity of absorption bands in the region of valence and deformation vibrations of water molecules up to their complete disappearance at temperatures of 973 K and above. In this case, infrared spectra are formed, typical for anhydrous phosphates. The complex character of the spectra of all synthesized chromium-nickel-phosphate catalysts and the presence of several absorption maxima corresponding to valent degenerate oscillations of the orthophosphate ion is due to the distortion of the structure itself of the tetrahedron due to strong hydrogen bonds. Such a complication of the phosphate ion spectrum, due to the distortion of the tetrahedron in real crystals and the decrease of its symmetry, is possible due to the low symmetry of the environment; permeation of phosphate ion by water molecules due to the formation of intermolecular hydrogen bonds; appropriate coordination of phosphate ion with cations of metals. At the same time, the energy of the hydrogen bond formed between the water molecule and the anion of salt increases with the growth of the proton-acceptor capacity of the anion itself. The frequency, intensity, assignment and shape of oscillations in IR absorption spectra are determined and their connection with phase transformations is established. The process of hydration and coordination of cations in the structure of samples has been investigated, the structure of anions has been analyzed, and the peculiarities of their configuration have been analyzed.