The direct oxidation of toluene to cresols with nitrous oxide as the oxidant was carried out over a ZSM-5 zeolite catalyst under gaseous and supercritical conditions (395 degrees C and 0.5, 7, 12 MPa; 420 degrees C and 15 MPa). The supercritical oxidation is characterized by a significantly greater productivity as compared to the gas-phase process. Successful in situ regeneration of the deactivated catalyst during the transition from the gas-phase to the supercritical process has been demonstrated.

The influence of the ratio of active components (Fe and Cr) on the catalytic activity of FeCr/C catalysts in the oxidative dehydrogenation of ethane with CO2 was analyzed. The best results were achieved on the 2Fe3.7Cr/C catalyst, in which the Fe : Cr ratio corresponded to the stoichiometry of iron(II) chromite FeCr2O4. The physicochemical characteristics of the prepared catalysts were determined and analyzed (XRD, XPS, magnetometry). Based on the totality of the data obtained, it is possible to assume the presence of the iron(II) chromite phase.

The influence of alkaline and acid pretreatments of Sibunit carbon support on the catalytic properties of Fe–Cr/С oxide systems was studied for the process of oxidative dehydrogenation of ethane with CO2 in a temperature range of 650–750°C. It has been established that alkaline treatment promotes the active occurrence of the Boudoir–Bell reaction, while acid treatment slightly increases ethane conversion with greater carbonization of the catalyst surface.

The catalytic oxidation of benzene with nitrous oxide (N2O) over ZSM-5 zeolite has been carried out in a continuous-flow reactor under supercritical conditions and compared with the results of the gas-phase reaction. Aromatic substrates and nitrous oxide under the conditions of supercritical experiments (300-435 degrees C, 6.0-18.0 MPa) are both reagents and the supercritical medium. It has been established that the productivity of the supercritical oxidation of benzene into phenol significantly exceeds the productivity of the gas-phase process owing to the limited reversible deactivation of the catalyst under supercritical conditions and the in situ removal of the coke precursors by the dense reaction medium. In addition, it has been demonstrated that a successful in situ regeneration of the deactivated oxidation catalyst can be carried out during the transition from gas-phase reaction conditions to supercritical conditions in one experiment.

Hydrolysed lignin has been depolymerized in sub- and supercritical water–ethanol medium (340–700 K) with various ethanol concentration (7, 51, 95 wt%). The structure of solutions obtained has been investigated by dynamic light scattering, IR-spectroscopy, SEC, HPLS and 2D-NMR. The concentration of depolymerized lignin is 1.4–6.2 g/L depending on the temperature and ethanol concentration. Solutions of depolymerized lignin are structurally heterogeneous, they contain particles of different sizes: small (up to 4 nm), medium (7–14 nm) and large (100–130 nm). It has been found that, for a moderate ethanol concentration (51 wt%), the transition to the supercritical region occurs at 570 K. The maximum number of particles of 1–4 nm are formed up to the critical point. Under the supercritical conditions, the depolymerization is more pronounced leading to the formation of both particles smaller than 1 nm and large particles. Increasing the ethanol concentration favors the increase in the dissolved lignin concentration, but large particles are preferably formed. Molecular dynamics simulation has been performed to clarify the structure of small particles. The model for simulation includes lignin monomers (coniferyl alcohol molecules and radicals) in the water–ethanol medium at 570 K. The lignol–water–alcohol near-critical mixture is heterogeneous, as it contains aqueous, alcoholic and mixed water–alcoholic clusters, both with and without lignol involvement, as well as lignol agglomerates. The inclusion of radical species in the model improves the description of lignol aggregation.

CO2 conversion via hydrogenation over iron-based catalysts on non-carbon supports produces mainly CO or methane by the Sabatier reaction, while the formation of C2+ hydrocarbons is of greatest interest. CxHy production from CO2 may be considered as a two-step process with the initial formation of carbon monoxide by the reverse water gas shift reaction followed by the Fischer-Tropsch synthesis (FTS). In the present work CO2 hydrogenation over iron-based catalysts (Fe, FeCr, FeK) deposited on a carbon carrier has been studied. The catalyst structure has been investigated by XRD, TEM, XPS, Mössbauer spectroscopy and in situ magnetometry. Spinel-type oxide phases (magnetite Fe3O4; maggemite γ-Fe2O3, and, in the case of FeCr/C catalyst, iron chromite Fe1+xCr2-xO4) are formed on the catalysts, and they contribute exclusively to the CO production. Iron carbides, active in FTS, are formed on Fe- and FeK-catalysts during pre-activation in reducing environment and then during the reaction. The reaction over the 20Fe1K/C catalyst in supercritical high-density CO2/H2 substrate (400 °C, 8.5 MPa) leads to 72 % selectivity for C1-C12+ hydrocarbons (alkanes and alkenes). Under the same conditions, iron carbides do not form on the FeCr/C catalysts, and CO2 hydrogenation results in the CO formation with the selectivity of 90-100 %.

The paper describes the pyrolytic transformation of hydrolysis lignin in 1,4-dioxane at a temperature of 250°C and a pressure of 13.0 MPa and the subsequent Ru/C-catalyzed hydrogenation of the products at a temperature of 250°C and a pressure of 10.0 MPa in an autoclave. It has been found that the thermal pyrolysis of hydrolysis lignin with 1,4-dioxane and the catalytic hydrogenation of pyrolysis products are accompanied by C−O and C−C bond cleavage and formation of a products mixture consisting of soluble oligomer and monomer phenol derivatives, products of their hydrogenolysis and hydrogenation, and also mixtures of C1−C5 gas hydrocarbons and C2−C5 alcohols, and ethers formed mainly during the destruction of the solvent (1,4-dioxane) under the reaction conditions.

The oxidative dehydrogenation of ethane into ethylene using CO2 as an oxidant at temperatures of 650–750 °C was carried out over Fe/C, Cr/C and Fe–Cr/C catalysts deposited on a carbon support. Before and after the reaction the catalysts were investigated by X-ray powder diffraction (XRD), in situ magnetometry and transmission electron microscopy methods. The correlation between activity of Fe/C, Cr/C and Fe–Cr/C catalytic systems and their phase composition was established.

Hydrolysis lignin was treated with sub-and supercritical water (523-723 K and 10 MPa). As a result, depoly-merization of lignin to mono-and oligolignols occurs. SEC data show water-soluble particles up to 4 nm after treatment of lignin by subcritical water (523 K and 10 MPa). After further treatment with supercritical water (723 K and 10 MPa), the concentration of water-soluble particles decreases by 2-3 times; and their size increased up to 10 nm. Molecular dynamics simulation of a model lignin particle in aqueous medium under standard (298 K, p = 0.997 g/cm3) and supercritical (673 K, p = 0.133 g/cm3) conditions was performed. Based on modeling, lignol monomers surrounded by solvate shells and water-soluble particles of lignin oligomers with a gel-like structure were identified as the structural units of the solutions. Under supercritical conditions, it causes the different ways of transformation of the system: further destruction of individual lignol molecules or condensation of lignols with the formation of insoluble precipitate.

The transformation of hydrolysis lignin in water under sub- and supercritical conditions (320–800 °C, 10.0 MPa) in the presence of iron(iii) ions was studied. At temperatures above 400 °C, two processes are most significant: deep depolymerization of lignin to phenolic monomers and condensation of aromatic moieties of lignin into carbonaceous deposits. In the presence of Fe3+ ions, the content of monomeric phenols increases 3–4-fold, which is indicative of the catalytic effect of iron in lignin depolymerization. When the reaction temperature increases from 400 to 660 °C, the content of monomeric products (mainly, phenol and guaiacol) increases from 1.8 to 7.5 wt.

Aqueous solutions of depolymerized lignin with a concentration of 12 to 15 g/L are obtained by treating an aqueous suspension of hydrolysis lignin (LG-PP) for 4 hours at 250°C and 10 MPa. The transformation of lignin in the resulting solution is studied at sub- (320°C, 30 MPa) and supercritical (400–650°C, 30 MPa) parameters in a flow-type reactor. It is shown that the degree of depolymerization of lignin increases with increasing temperature and reaches its maximum value at 650°C; the process results in the formation of hydrocarbons of various groups including derivatives of benzene and phenol. Intensive gasification of lignin with the production of gas mixtures containing up to 40 vol

Исследован процесс окислительного дегидрирования этана (ОДЭ) при повышенном давлении на смешанном оксидном катализаторе MoVNbTeO*. Установлено, что при проведении реакции при 280 °С с ростом давления от 0,1 до 10,0 МПа доля от общего количества прореагировавшего кислорода, расходуемого на образование этилена, снижается со 100 до 68 %, что может свидетельствовать о возрастании роли хемосорбированного кислорода в процессе ОДЭ при высоком давлении. При этом производительность по этилену при 280 °С и 10,0 МПа оказывается выше по сравнению со значением, полученным при 360 °С и 0,1 МПа. The process of oxidative dehydrogenation of ethane (ODE) at elevated pressure on mixed oxide catalyst MoVNbTeO* has been investigated. It was found that when the reaction is carried out at 280 °C with an increase in pressure from 0,1 to 10,0 MPa, the proportion of the total amount of reacted oxygen consumed for the formation of ethylene decreases from 100 to 68 %, which may indicate an increase in the role of chemisorbed oxygen in the ODE process at high pressure. In this case, the productivity for ethylene at 280 °C and 10,0 MPa higher compared to the value obtained at 360 °C and 0,1 MPa.

Обработкой водной суспензии гидролизного лигнина (ЛГ-ПФ) при 250 °С и 10 МПа в течение 4 ч получены водные растворы деполимеризованного лигнина с концентрацией 12-15 г/л. Превращение лигнина в полученном растворе изучено при суб- (320 °С, 30 МПа) и сверхкритических (400-650 °С, 30 МПа) параметрах в реакторе проточного типа. Показано, что степень деполимеризации лигнина повышается с ростом температуры и достигает максимального значения при 650 °С; процесс протекает с образованием углеводородов различных групп, включая производные бензола и фенола. При температурах выше 600 °С происходит интенсивная газификация лигнина с получением газовых смесей, содержащих до 40 об. % водорода. Aqueous solutions of depolymerized lignin with a concentration of 12-15 g/l were obtained by treating an aqueous suspension for 4 hours at 250 °C and 10 MPa. The transformation of lignin in the resulting solution was studied at sub- (320 °C, 30 MPa) and supercritical (400-650 °C, 30 MPa) parameters in a continuous flow reactor. It is shown that the degree of lignin depolymerization increases with increasing temperature and reaches its maximum value at 650 °C; the process results in the formation of hydrocarbons of various groups, including derivatives of benzene and phenol. At temperatures above 600 °C, intense gasification of lignin occurs with the production of gas mixtures containing up to 40 vol. % hydrogen.

Hydrogenation of phenol in aqueous solutions on Pt-Ni/SiO2, Pt-Ni-Cr/Al2O3, Pt/C, and Ru/C catalysts was studied at temperatures of 150–250 °C and pressures of 40–80 bar. The possibility of hydrogenation of hydrolysis lignin in an aqueous medium in the presence of a Ru/C catalyst is shown. The conversion of hydrolysis lignin and water-soluble sodium lignosulfonate occurs with the formation of a complex mixture of monomeric products: a number of phenols, products of their catalytic hydrogenation (cyclohexanol and cyclohexanone), and hydrogenolysis products (cyclic and aliphatic C2–C7 hydrocarbons).

Highly selective and active phases in the ethane dehydrogenation were formed on the inner wall of stainless-steel reactor after its long-term using in the process at 650-750 degrees C. The conversion of ethane at 650 degrees C reached up to 40% with ethylene selectivity closed to 90%. Fe-Cr-Ni and Fe-Cr oxides catalysts supported on carbon were created for CO2-mediated oxidative dehydrogenation of ethane (ODE) based on SR-XRD analysis of the inner wall of the steel reactor. In the case of Fe-Cr-Ni/C catalyst, the ethylene selectivity decreased and the catalyst was rapidly deactivated by coke deposits. On Fe-Cr/C catalyst, the ethylene selectivity was 82% and ethane conversion was above 20% at 700 degrees C. It was found that phase FeCr2O4 forms on the surface of Fe-Cr/C catalyst, which, as we assume, is responsible for high stability of the catalyst and its high selectivity of ODE with CO2.

The successful use of a palladium membrane to enhance the yield of benzene–toluene–xylene (BTX) fraction in n-butane aromatization at 530°C and 95atm on a Ga/H-ZSM-5 catalyst has been shown. Removal of hydrogen from the reaction zone through the palladium membrane led to an increase in both the n-butane conversion and the selectivity of the BTX fraction formation.

The problem of hydrogen storage in liquid organic hydrogen carriers is not only the choice of an appropriate organic substrate, but the development of a selective and active catalyst containing as low as possible noble metals. A synergistic effect of increasing conversion and selectivity in bicyclohexyl dehydrogenation to biphenyl on trimetallic Pt-Ni-Cr/C catalysts with an extremely low Pt loading (0.1 wt %), compared with bimetallic Ni-Cr/C and Pt/Ni/C systems, due to the supporting of platinum on nickel-chromium nanoparticles was established for the first time. The TOF values (mmol (H-2)/gPt min) for hydrogen evolution under conditions of the reaction of bicyclohexyl dehydrogenation (320 degrees C, 0.1 MPa) on Pt supported onto a Ni-Cr/C composite exceed by two orders of magnitude the values found for the two-component catalysts. The maximum amount of the evolved hydrogen correlates to the selectivity of the complete dehydrogenation of bicyclohexyl into biphenyl on the Pt-Ni-Cr/C catalyst. The formation of a Ni-Cr solid substitution solution in a Ni-Cr composite deposited on a carbon carrier is shown by magnetometry, XRD, and TEM methods. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Catalyst FeCrOx/C in the course of oxidative dehydrogenation of ethane with carbon dioxide to ethylene at temperatures of 600–700 °C was found to undergo in situ regeneration with CO2 to give a stoichiometric amount of CO by the Boudoir–Bell reaction with the surface carbonized material.

Dedicated the memory of Akademician Valery Vasilievich Lunin, a friend, colleague, teacher, founder and leader of the research into application of supercritical fluids in chemistry. This review analyzes the rapidly developing applications of supercritical fluids, mainly supercritical carbon dioxide, in catalysis, chemistry of high-molecular-weight compounds, and medicinal chemistry in Russia and abroad. It considers the methods of catalyst preparation based on impregnation of inorganic and organic supports with metal-containing compounds, immobilization of organometallic and metal complex reagents in matrices of oxide and polymer supports, and deposition processes employing supercritical fluids. An analysis is presented of the prospects for applying CO 2 and some organic compounds, such as aliphatic alcohols, in sub- and supercritical states as reactants and (or) solvents for catalytic reactions of hydrocarbon isomerization and cracking, hydrogenation, dehydrogenation, oxidation, etc., including the asymmetric reactions. The review discusses processes of synthesizing and modifying polymer materials for various purposes, including aerogels, foams, and composites impregnated with photochromes, in a supercritical fluid medium. Special attention is paid to supercritical one-pot processes, which make the techniques of obtaining new materials simpler, less expensive, and more efficient. The work investigates the effect of supercritical CO 2 on the morphology, gas separation characteristics, and dielectric properties of polymers. One of the promising applications of supercritical fluids in medicine is the use in transplantology and pharmacology, for example, for the preparation of drug polymorphs with higher bioavailability. The review also provides an overview of the recent data on the use of EPR spectroscopy for studying the properties of supercritical fluids, including those exhibited in the vicinity of the critical point and identifying the intermediates of chemical reactions in such media.