DIFFERENTIAL AND THERMAL ANALYSIS OF COMPLEX CATALYTIC SYSTEM OF TYPE хСо3(РО4)2уNi3(РО4)2

Abstract

Individual phosphates of cobalt and nickel and seven new complex oxide catalytic systems based on cobalt phosphate were synthesized by modifying it with ions of Nі 2+ type xCo 3 (PO 4 ) 2 ×yNi 3 (PO 4 ) 2 with different content of both phosphates having acidic surface properties. The modern methods of analysis have studied the composition, structure and some physical and chemical parameters of all synthesized samples. The influence of the synthesis conditions on the nature of the formation of their structure and the corresponding physico-chemical and catalytic properties was studied with the help of differential-thermal analysis. It is established that for synthesized binary samples, various forms of water that are part of their composition are characteristic: adsorbed, structural, crystallization, constitutional, etc. Allocating them from the structure of catalysts in the process of heat treatment is accompanied by various effects and corresponding endo-effects. In this case, the kinetics of water thermosorption from the surface and from the volume of internal pores depends on the nature of the interaction between the molecules in the adsorption layers and water molecules on the surface. In the allocation of adsorbed water from phosphate catalysts, the change in the type of anion is not observed. However, the elimination of crystallization, and especially constitutional water, is accompanied by a rupture of chemical bonds, intense diffusion of water vapor from the lattice and rearrangement of phosphate anion. All synthesized phosphates have different curves of DTA and DTG, which are different from individual phosphates of cobalt and nickel, and with each other. It is established that on all DTG curves of K-1-K-4 samples quite significant peaks of endo-effects are observed in the region T = 473-763 K. They indicate the presence of various interactions of adsorbed aqueous layers on the surface of samples of phosphates: the layers of condensed water (I) (in the region T = 450-550 K), water in mesopores (II) (in the region T = 620-670 K), and adsorption layers of water directly on the surface of phosphates (III) (in the region T = 730-770 K). After calcining at T = 973 K and at higher temperatures, all synthesized complex catalytic phosphate systems exist in the form of anhydrous salts, which is confirmed by the data of X-ray diffraction, IR spectroscopic and chemical analyzes.