Alexander P. Ilyin

A series of oxide catalysts modified with potassium cations, 1–5% K₂О/CoFe₂O₄, with a spinel structure were obtained via mechanochemical synthesis. The obtained samples were studied via X-ray powder diffraction, nitrogen adsorption–desorption, temperature-programmed reduction with hydrogen, and temperature-programmed desorption of oxygen. It was shown that an increase in the potassium content leads to a significant decrease in the crystallinity of the oxide, an increase in the specific surface area, and the formation of weakly bound oxygen species; this favors an increase in the catalytic activity of the samples in the decomposition of nitrous oxide at 150–400°C. The most active catalyst was 5% K₂О/CoFe₂O₄, which had the maximum content of weakly bound oxygen species. It was determined that the presence of oxygen or water in the rection mixture decreases the activity in the low-temperature catalytic decomposition of N₂O.

The acidity characteristics of zeolite are highly significant, and understanding the acidic properties is essential for developing new types of zeolite catalysts. Zeolite membranes were synthesized using metakaolin, sodium hydroxide, and alumina with a molar ratio of 6Al₂Si₂O₇:12NaOH:2Al₂O₃ as the starting ingredients. X-ray diffraction, scanning electron microscopy, and infrared spectroscopy were used for this study. N₂ adsorption measurements determined the surface areas of the SOD zeolite membrane (115 m²/g) and the LTA membrane (150 m²/g). The units of absorbed water vapor were 40 and 60 wt% for the SOD membrane and the LTA membrane, respectively. The strength and number of acid sites of the synthesized LTA and SOD zeolite membranes were determined by temperature-programmed desorption of ammonia. As a result, the value of the total acidity of the LTA zeolite membrane is in the range of 0.08 × 10¹⁹ units/m² while that of the sodalite membrane is an order of magnitude lower and is 0.006 × 10¹⁹ units/m². The apparent activation energy values for desorption of ammonia from LTA and SOD zeolite membranes were calculated using data on the kinetics of desorption of ammonia at different heating rates. It was found that at temperatures below 250 °C, the degree of conversion of the activation energy values is no more than 35 kJ/mol, which corresponds to the desorption of physically bound ammonia. An increase in the activation values up to 70 kJ/mol (for SOD) and up to 80 kJ/mol (for LTA) is associated with the desorption of chemically bound ammonia from the samples.

The paper defines the conditions for the synthesis of hydrogen sulfide adsorbent based on zinc oxide from basic zinc carbonate in order to produce strong, porous and non-dusting pellets of a sulfur-adsorbing mass. It is proposed to prepare the adsorbent by mixing nanocrystalline and coarsely dispersed ZnO. It was proven that the introduction of solutions of carboxymethyl cellulose and hydroxypropyl cellulose into the extraction paste makes it possible to reduce the fraction of plastic deformations in the ZnO suspension from 79.8 to 56.1%. In this paper the rheological properties of zinc oxide are investigated. According to the Maxwell–Shvedov and Kelvin model, all the studied systems belong to the fourth structural-mechanical type. Tests of a sulfur adsorbent based on zinc oxide suspensions showed that in the temperature range of 300–400°C in the reaction gas mixture H₂S 10%, N₂ 90%, there are completely no sulfur compounds at the outlet. It has been established that the formability of the ZnO-based paste is possible at an optimum moisture content of 33.4%.

A study is performed of the procedure for preparing a catalyst of the decomposition of nitrogen(I) oxide. Decomposition catalysts were prepared through the mechanochemical synthesis of cobalt ferrite from a mixture of iron and cobalt oxalates. It is established that preliminary mechanochemical activation of the initial components in a roller ring vibration mill allows the temperature of cobalt ferrite synthesis to be reduced to 300°C, yielding a product with a more developed specific surface area and porous structure. The catalytic properties of cobalt ferrite with different ratios of the main components (CoO : Fe₂O₃ = 0.7–1.3) are studied in the temperature range of 100–500°C. It is shown that raising the content of CoO in the composition of cobalt ferrite to a ratio of 1.3 lowers the temperature of the 50% decomposition of N₂O from 420 to 370°C. The effect water vapor, O₂, and H₂ have on the reaction is revealed. The effect pressure and temperature have on the activity of a catalyst based on cobalt ferrite is established for the decomposition of N₂O.

This work discusses the optical systems with brightness amplification based on two copper bromide brightness amplifiers for studying the combustion of aluminum-based nanopowders. It is proposed to use a system with brightness amplification and independent illumination–bistatic laser monitor to increase the brightness and sharpness of images. Independent illumination is realized using a second copper bromide laser and makes it possible to increase the exposure of the object under investigation in comparison with the conventional laser monitor with one brightness amplifier. In addition to independent illumination, a two-channel laser monitor is proposed to examine the surface of burning materials with different magnifications in one area of the sample, as well as simultaneously in two areas of the sample. The delay between the lasing pulses of the brightness amplifiers can be adjusted with high accuracy so that the radiation from one amplifier does not affect the images of the other. The proposed experimental technique makes it possible to investigate the surface of powder materials during high-temperature combustion, accompanied by intense glowing and scattering of combustion products. This article presents the results of real-time visualization of the surface of burning metal nanopowders and mixtures using bistatic and two-channel laser monitors.

The article analyzes the work of the department for the conversion of carbon monoxide with water vapor to hydrogen as part of the ammonia synthesis unit. The effect of temperature and duration of operation of the medium-temperature conversion catalyst on the technical and technological parameters of the process is shown. The catalytic conversion of carbon monoxide is an important component of the hydrogen production process in the industrial technology of deep processing of natural gas. In modern ammonia synthesis units, the conversion process takes place in two stages: first, at a temperature of 360 - 430 degrees C on iron-chromium, and then at 190 - 260 degrees C on a copper-containing catalyst. It was found that along with the main products (H-2, CO2), the presence of undesirable impurities of ammonia, amines, alcohols, acetates and formates was detected in the synthesis gas. It is shown that the main by-product at the stage of medium-temperature conversion is ammonia, the content of which in the condensate reaches 80-85%. Methanol is formed as a by-product both at the stage of medium-temperature (9-13%) and low-temperature conversion (87-91%). Most of the methanol generated during the conversion process is condensed with water in separators, while the rest goes to the CO2 removal system. In the separator, where the temperature is 160-162 degrees C, on average 68% of methanol remains in the gas phase, and in the separator, where deeper gas cooling is applied to 72 degrees C, about 81% of methanol remains in the condensate. To decrease the methanol content, it is necessary to lower the conversion temperature and increase the gas space velocity. Under the conditions of ammonia production from methanol and ammonia, a mixture of amines of varying degrees of substitution is formed, predominantly methylamine (CH3)NH2 and demytylamine (CH3)(2)NH2. Moreover, about 35-40% of the formed amines goes into condensate, and most of it remains in the gas phase and goes to the stage of cleaning from CO2. In the production of ammonia, solutions based on potash - K2CO3 are used to clean the converted gas from CO2, which absorb organic impurities, which are formed mainly at the stage of low-temperature conversion. Impurities impair the operation of the purification stage and cause foaming of solutions. One of the reasons for foaming is the presence of organic matter degradation products in the solution.

The acid-base properties of cobalt ferrite synthesized by the mechanochemical method with different ratios of the main components Fe₂O₃ : Co₃O₄ have been investigated using the temperature-programmed desorption of ammonia, IR spectroscopy using adsorbed pyridine with ammonia, and the Hammett indicator method. A comparison of the results for the total content of Lewis and Brønsted acid sites by three methods has shown that all three samples were quite similar, with a probability of 0.5%. The introduction of cobalt oxide into the composition of cobalt ferrite leads to an increase in the concentration of Brønsted and Lewis centers with a simultaneous increase in the number of strong basic centers determined by the temperature-programmed desorption of ammonia. The indicator method is the most informative method for a quantitative study of the acid-base properties of the cobalt ferrite surface, since it allows one to assess the concentration and strength of Lewis and Brønsted acid sites and basic sites.

The physicochemical characteristics of modern catalysts for the medium-temperature conversion of carbon monoxide to hydrogen in the production of ammonia were studied by X-ray diffraction, scanning electron microscopy, gas chromatography, and thermogravimetric and laser dispersion analyses. It was shown that, along with iron oxide, the catalysts contained promoter additives of Cr, Cu, Ca, and Mn compounds in a total concentration of 1–9 wt%. The investigated commercial catalysts have a monodisperse porous structure with a pore size of up to 10 nm and a large surface area from 70 to 120 m²/g. The catalytic activity of the samples was estimated by the conversion of CO in a flow-type plant. At 2.2 MPa and 340 °C it was 89–91%. The drawback of the catalysts was that the condensate contained rather much ammonia (27.6–45.6 mg/L). It was established that using calcium and copper ferrites and nickel oxide as promoters makes it possible to obtain a catalyst that is not inferior in activity to commercial analogs but has a higher selectivity by reducing the ammonia content of the condensate by 20–30%.

Relationship between the amount of acidic and basic sites of cobalt ferrite and its catalytic properties in the decomposition of nitrogen(I) oxide has been established. The Hammett’s indicators method and thermal desorption of ammonia have revealed the distribution of acid-base sites depending on the ratio of the Fe₂O₃–Co₃O₄ components. It has been shown that the increase in the amount of the basic sites reduces the temperature of N₂O decomposition by 122°С. The nature of the acidic and basic sites at the CoFe₂O₄ surface has been identified using IR spectroscopy.