Vol 64, No 5 (2023)

Biocatalysis, both in homogeneous and heterogeneous modes, is an independent interdisciplinary direction of scientific and practical research of predominantly one-stage processes of conversion of initial reagents (substrates) into valuable products that are in demand on the market, with the participation, as a rule, of one enzyme as a catalyst. Biocatalytic single-enzyme processes, which have all the specific features of enzymatic catalysis, are alternative and quite competitive compared to traditional chemical production. This review provides information on the investigations and success of Russian research groups/laboratories that have been actively and productively working in the field of the biocatalysis over the past decades and have practical developments protected by Russian patents, which, under favorable circumstances, can be offered to commercial enterprises/companies for testing and use on a laboratory and/or semi-industrial scale with the prospect of industrial scale-up. In the review, special attention is paid to targeted systematic studies of lipolytic enzymes (lipases), which have a unique ability to catalyze reactions in organic solvents, including esterification and transesterification, which result in the production of valuable products of organic synthesis such as various esters. Lipases are active components of heterogeneous biocatalysts (BCs) prepared by attachment (immobilization) of these enzymes on the surface of solid supports and adsorbents. The review briefly describes the results of study by domestic research teams, provides a complete bibliography of their works, which contains information about the methods for preparing BCs, their catalytic properties (enzymatic activity, substrate specificity, operational stability), as well as the conditions for carrying out biocatalytic processes involving developed BCs such as the synthesis of acrylamide and various esters. Taking into account the average activity (A), close to the activity measured at the half-inactivation time (t_1/2), and operational stability, characterized by the value t_1/2, a rather rough assessment of the productivity of the BCs was carried out based on the amount of produced valuable product (in tons) per 1 kg of developed biocatalyst.

Synthesis gas is the cornerstone of many chemical processes for manufacturing a broad range of petrochemical products. In this work, a mathematical model was developed for investigation of the CO₂ reforming of methane in a catalytic packed bed reactor. To simulate the reformer, a pseudo homogenous two-dimensional mathematical model was developed and the resulting nonlinear second order partial differential equations were solved using the finite difference method. It was assumed that equilibrium reverse water gas shift reaction always takes place in the reactor to adjust H₂/CO ratio (≤1). The effect of operating conditions, including bulk density, porosity, inlet gas and wall temperature, reactor diameter, total molar flow of gas and inlet CH₄/CO₂ ratio on the reactor performance were investigated. Finally, the study investigated the effect of H₂/CO ratio on the outlet synthesis gas product at the range of 0.7–1. The validity of the model was investigated and the deviation between the model results and the experimental data was acceptable.

ZnO and CoFe₂O₄ nanoparticles were synthesized via co-precipitation route and the composites ZnO/CoFe₂O₄ (ZC1 (3 : 2), ZC2 (2 : 3), ZC3 (1 : 4)) were obtained by the sonochemical process. X-ray diffraction (XRD) study reveals the existence of two phases in the material: a hexagonal wurtzite structure of ZnO and a cubic lattice structure of CoFe₂O₄. The flower-shaped rod-like structure of ZnO nanoparticles and agglomeration of CoFe₂O₄ nanoparticles are observed using field emission scanning electron microscopy (FESEM). The elemental composition of the synthesized material is confirmed through energy dispersive spectroscopy (EDS). Light absorbance performance of the material is determined by using UV-visible spectroscopy. Further, the band gap of pure and composite materials is calculated by employing a Tauc plot. Fourier transform infrared spectroscopy (FTIR) reveals the creation of cationic and anionic bonding at different interstitial sites. The magnetic properties of the material were studied using vibrating sample magnetometer (VSM). Various magnetic parameters, for instance M_s, M_r, H_c, n_B, and M_r/M_s ratio were traced from M–H loops. The photocatalytic performance of the materials under UV irradiation is examined through degradation of methylene blue (MB) dye. The efficiency of composite ZC1 is found to be better than that of pure ZnO, CoFe₂O₄ and composites ZC2 and ZC3.

Bimetallic heterogeneous catalysts based on SBA-15 containing molybdenum and iron oxides were studied in the oxidation reactions of model mixtures of organosulfur compounds. Iron additive (in the form of iron(III) oxide) in the amount of 0.05 wt % to the catalyst 5%Mo/SBA-15 turns out to be the most effective. The catalysts were confirmed by a complex of physicochemical methods: low-temperature adsorption-desorption of nitrogen, X-ray phase analysis, transmission electron microscopy, X-ray photoelectron spectroscopy. The influence of the main oxidation parameters (reaction time, temperature, composition and amount of catalyst, amount of oxidizer) on the conversion of dibenzothiophene as a component of the model mixture weas investigated. Optimal oxidation conditions that allow to achieve total transformation of the substrate were selected: H₂O₂ : S = 2 : 1, 0.5 wt % of the catalyst FeMo/SBA-15, 60 min, 60°C; catalysts can be used for at least 5 cycles without loss of activity during their intermediate washing from oxidation products.

The catalytic properties of nCrO_x/Al₂O₃ nanoparticles (n = 4.8 ± 0.05 wt %) tested in the isobutane dehydrogenation reaction which were obtained by laser synthesis in various gases are studied in detail for the first time. Laser synthesis of 4.8% CrO_x/Al₂O₃ nanopowders was carried out by the vaporization of 5.0% Cr : α-Al₂O₃ ceramic targets using cw CO₂ laser irradiation in an inert, oxidizing and reducing gaseous environment in a vaporization chamber: in an Ar medium; Ar with addition of O₂, H₂ and CH₄ at concentrations of 20, 30, and 13 vol. %, respectively. The role of the gas medium during the synthesis of 4.8% CrO_x/Al₂O₃ nanopowders in their catalytic properties (activity, selectivity, conversion, and stability in the reaction) was determined. A comprehensive study of the physicochemical properties of the obtained nanocatalysts was carried out using XRD, TEM, UV-Vis DRS, and Raman techniques. According to XRD data the phase composition is predominantly consists of γ-Al₂O₃ with the beginning of the transition to δ-Al₂O₃. According to the TEM results, the shape of nanoparticles is spherically symmetric with an average particle size d_m = 15 nm. Using the UV-Vis DRS method, charge states of Cr^q+ (q = 3, 6) in different coordination (Cr⁶⁺(T_d) and Cr³⁺(O_h)) and its different ratios depending on the gas atmosphere used in the process of laser vaporization were revealed in the obtained 4.8% CrO_x/Al₂O₃ nanopowders. Nanosized 4.8% CrO_x/Al₂O₃ catalyst prepared in an atmosphere (Ar + H₂) demonstrated the highest values of isobutane conversion (39%) and isobutylene selectivity (90.7%); the lowest corresponding values of conversion (18.8%) and selectivity (85.6%) were typical for the sample obtained in the atmosphere (Ar + CH₄). Thus, the most active and selective in the isobutane dehydrogenation reaction was the 4.8% CrO_x/Al₂O₃ nanocatalyst synthesized in the (Ar + H₂) medium, and the presence of methane during vaporization led to the initial surface carbonization, which prevents the access of reacting molecules to it.

Nickel-based Ni–Ce_{1 – x}Zr_xO₂ catalysts were prepared by Pechini method and their catalytic performance towards CO₂ methanation reaction was studied. It was shown that the catalysts exhibit high catalytic activity comparable to the activity of industrial methanation catalyst NIAP-07-05. The catalysts were characterized using a complex of X-ray diffraction methods with experiments on synchrotron radiation, high-resolution electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It is shown that the preparation method makes it possible to achieve a high dispersion of nickel-containing particles formed during the decomposition of the Ni–Ce–Zr–O substitutional solid solution obtained during the synthesis. However, due to the decorating effect, the surface of nickel-containing particles is poorly accessible to reagents. For this reason, the Ni–Ce_{1 – x}Zr_xO₂ catalysts obtained by the Pechini method are less active than the supported Ni/Ce_{1 – x}Zr_xO₂ catalysts.