INFRARED SPECTROSCOPIC ANALYSIS OF COMPLEX OXIDE CATALYST 50%Cu3(PO4)2•50%Ni3(PO4)2

Abstract

It is established that the frequencies and intensities of the absorption bands of the infrared spectra of the obtained air-dried sample 50%Cu3(PO4)2∙50%Ni3(PO4)2 and calcined at the optimum heat treatment temperature of 600оС are characterized by significant absorption in the valence (3460-3020 cm-1) and strain (2360-1400 сm-1) vibrations of hydroxyl OH-groups of water molecules. Valence vibrations of phosphate ion are most manifested in dehydration products in the form of clear bands in the absorption frequency range 1110-410 сm-1. For the investigated sample, three absorption bands were observed in the region: 3188,72 сm-1, 1621,84 сm-1 та 1434,78 сm-1. They confirm the existence of two types of crystalline hydrate water molecules, which are characterized by different hydrogen bonding energies. In the process of heat treatment of the synthesized sample in the temperature range of 120-700оС , the process of dehydration occurs. In this case, the intensity of the absorption bands in the region of valence and strain vibrations of water molecules gradually decreases in the obtained IR spectra. The phenomenon of complication of the spectrum of orthophosphate ion by additional absorption bands is obviously associated with the distortion of the tetrahedron structure in real crystals and the reduction of its symmetry. It can be a consequence of both low symmetry of the environment and perturbation of the orthophosphate anion РО43– by water molecules when intermolecular hydrogen bonds occur. It may also be due to possible additional coordination of orthophosphate anion with metal cations Сu2+ and Ni2+. Calcination of the sample at the final heat treatment temperature of 700оС leads to an anhydrous orthophosphate system. This will lead to a decrease in the value of surface acidity and catalytic inertness of the sample.
 Keywords: catalysts; heterogeneous catalysis; phosphates; complex oxides; oxidation; n-alkanes; hydrocarbons; ethane; ethylene; IR spectroscopy.