Vol 65, No 3 (2024): Специальный номер посвящен памяти Олега Наумовича Темкина

Approaches to revealing the mechanisms of catalytic reactions and, in particular, the mechanism of the catalytic action of catalysts for the processes of partial oxidation of light alkanes – oxidative coupling of methane (OCM) and oxidative dehydrogenation (OD) of C₂₊ alkanes – are considered. The development of ideas about the functioning of the group of the most effective catalysts for OCM and OD processes – supported mixed oxides containing tungsten, manganese and alkali elements – is analyzed. Arguments are given in favor of the hypothesis about the mechanism of the catalytic action of these systems that includes a reversible redox Mn²⁺ ⇌ Mn³⁺ transition, occurring with the participation of a melt based on alkali metal compounds – tungstate in the oxidized state and a mixed oxide containing manganese ions in the reduced state. The effectiveness of this transition, i.e. the reactivity of the oxidized form of the supported component with respect to the alkane molecule and of the reduced form with respect to the oxidizing agent (oxygen), and, accordingly, the catalytic process is determined by the intensity of the interaction (adhesion) between the melt and the support. The proposed mechanism explains the observed patterns of the catalytic process, including the dependence of the activity and selectivity of catalysts on the properties of the support and the composition of the supported component, and is confirmed by the available data obtained using physicochemical methods.

The work is directed to identifying the effect of copper or manganese oxide additives on the catalytic properties of the CeO₂–SiO₂ (CeSi) system containing silicon dioxide as a textural promoter in the preferential oxidation of carbon monoxide in excess hydrogen (PROX-CO). The CeSi catalyst was prepared by precipitation from salts in the presence of cetyltrimethylammonium bromide template, 5 wt % MnO_x/CeSi and 5 wt % CuO_х/CeSi were obtained by precipitation of modifiers from salts in the presence of potassium carbonate. The catalytic efficiency in PROX-CO increases in the series CeSi > Mn/CeSi > Cu/CeSi (at 200°C the time-averaged CO conversion values are 5, 19 and 78%, CO₂ selectivity values are 100, 65 and 59%). Characterization by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption-desorption, Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction with hydrogen demonstrated, that the presence of SiO₂ promotes the formation of highly dispersed and easily reduced CuOx clusters in close contact with CeO₂ particles, uniformly distributed over CeSi, and containing Cu⁺ adsorption centers. The Mn/CeSi system is characterized by an uneven distribution of manganese on the surface, a low number of MnO_x-CeO₂ contacts, and a low reduction ability of MnO_x in the low-temperature range (50–100°C).

The kinetics of reactions of liquid-phase hydrogenation of sodium acrylate on catalysts has been studied. Ni/SiO₂ with different amounts of deposited nickel were used as a catalyst, as well as samples with controlled partial deactivation of the surface by sulfide ion. Approaches to determining the amount of reduced metal on the catalyst surface and the amount of catalytic poison required to deactivate active centers are shown. Hydrogenation reaction rates and activity were measured. Kinetics were modeled, and rate constants of hydrogenation, adsorption, and desorption of hydrogen were obtained. The number of active centers and their ratio to metal atoms located on the catalyst surface were estimated.

The problem of selection and determining the values of descriptors for the properties of chemical reactions components in mathematical models for chemical processes is one of the essential ones when creating machine learning (ML) models used to describe and predict the functioning patterns of chemical systems. Current practice in the field mainly involves the use as the descriptors physical and chemical characteristics of the components of reaction systems (ionic radii, bond lengths, energies, and other parameters related to the structure and properties of specific molecules or particles) determined experimentally or by calculation. This work presents the results of the predicting of the integral kinetic dependences, as well as approaches to determine the values of descriptors for characterizing the properties of a set of simple palladium catalyst precursors when used in the Suzuki–Miyaura reaction. The problem stated has been solved by creating the ML models that take into account experimental kinetic data. The descriptors obtained as a result of training the models make it possible to satisfactorily describe the kinetic patterns of the Suzuki–Miyaura reaction with aryl chlorides under the so-called “ligand-free” catalytic conditions possessing higher sensitivity of the reaction to small changes in the conditions.