ИСТИНА

Catalysts were received by annealing of mixed nitrates Bi, Со, К; Bi, Са, K and Bi, Mg, K in air at 500-520°C. The crystal phase of as-prepared catalysts was identified by XRD, SEM, XPS methods. XRD data showed that the catalyst based on Bi-Co-K consists of phases Bi2O3, KBiO3, KCoO2; based on of Bi-Ca-K - of phases Bi2O3, Bi6K4O13, K0.75Ca0.25BiO3 and based on of Bi-Mg-K - of phases KBiO2 and MgO. With the help of SEM it is revealed that received catalytic systems crystallize in the form of aggregates. The surface of aggregates for Bi-Co-K catalyst is smooth. The sizes of formed aggregates are in the range 0-4.4µm (dominant size - 0.8µm). If the Bi-Cа-K system’ surface is smooth, the size of the aggregates is bigger and is in the range of 0-15µm (dominant size - 3.2µm). At identity of surface texture, the size of aggregates of the Bi-Mg-K catalytic system significantly differs from two previous and corresponds to 200-800nm (dominant size - 250 nm.). XPS was used to determine the chemical state of synthesized catalysts and soot/catalyst mixtures surfaces before and after oxidation. As a result, in the process of soot oxidation in presence of Bi – Mg – K and Bi- Co - K was detected that Bi4f 7/2 binding energy is about 158.8eV, the Co2p 3/2 - about 780.1eV, Mg 2p – about 49.6eV, K2p 3/2 - about 292.5eV. This corresponds to Bi3+, Mg2+, Co3+ and K+ oxidation levels. This gives evidence that in the process of soot catalytic oxidation the change of oxidation level of the elements forming catalytic system is not observed. At soot oxidation by oxygen in conditions of tight contact of soot with the catalyst all systems demonstrate high catalytic activity in the studied temperatures range. At non-tight contact observed is considerable drop of catalytic activity for systems Bi-Ca-K (Fig. A) and Bi-Mg-K (Fig. C). The Bi-Co-K (Fig. B) system shows high catalytic activity regardless of the type of contact with soot. As a result of soot oxidation in presence of the studied systems the changing of oxidation level of Bi, Co, Mg, K is not observed and realization of soot oxidation via carbothermal mechanism (redox catalysis) does not run. Most likely the catalytic action of these systems can be associated with formation and disintegration of oxygen-containing functional groups of soot surface to CO and CO2. Hypothetically, the key role in this process is assigned to potassium which presence is capable to strongly influence on the initiation of soot oxidation process and its further acceleration due to migration of potassium ion from the catalyst in the soot layer.