Thermovapour treatment (TVT) of SnO 2 and CaO oxides in an autoclave at 673 K leads to the formation of isometric CaSnO 3 perovskite-type crystals. TVT at 623 K leads to a previously unknown CaSn 2 O 4 (OH) 2 phase with lamellar crystals. The structure of the new compound CaSn 2 O 4 (OH) 2 was determined using powder X-ray diffraction and characterized with scanning electron microscopy, thermogravimetry–differential scanning calorimetry (TG-DSC) analysis, and IR spectroscopy. CaSn 2 O 4 (OH) 2 crystallizes in space group Aba 2 with Z = 4. The crystal structure consists of double layers formed from [SnO 6 ] octahedra alternating with layers formed from [CaO 8 ] tetragonal antiprisms. The TG-DSC study shows that the new compound CaSn 2 O 4 (OH) 2 is stable up to 973 K. The thermodynamic parameters of CaSn 2 O 4 (OH) 2 analysized using DFT in comparison with CaSn(OH) 6 and CaSnO 3 . The synthesized lamellar CaSn 2 O 4 (OH) 2 exhibits high catalytic activity and selectivity to C 6+ products in the aldol condensation of acetone at 673 K and 12.0 MPa.

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 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.

Ethanol over calcium stannate (CaSnO 3 ) catalyst under supercritical conditions (400 degrees C, 120 atm) is trans formed mainly into ethanal, ethyl acetate and 2-buten-1-ol. The process is accompanied by crystallization of the amorphous catalyst.

Переработку гидролизного лигнина в среде сверхкритического н-гексана осуществляли в две стадии: 1) термическая обработка лигнина в автоклаве при 250°С и 15 MПa в среде аргона; 2) гидрирование раствора полученных на первой стадии продуктов при 250°С и 9,0 MПa в присутствии катализатора Ru/C. Полученные на первой и второй стадиях продукты анализировали методами высокоэффективной жидкостной хроматографии, гель-проникающей хроматографии и газовой хроматографии, хромато-масс-спектрометрии и элементного анализа. На первой стадии степень деполимеризации составила 17 %; перешедшие в раствор в результате деполимеризации моно- и олигомерные фрагменты лигнина имеют молекулярномассовое распределение (ММР) в пределах от 65 Да до 270 кДа. Определен состав мономеров в продуктах деполимеризации первой стадии: моно-, ди, три- и тетраалкилпроизводные бензола (2,8 мас. %), гваякол и его 4-алкилпроизводные (0,6 мас. %), в том числе конифериловый спирт (0,06 мас. %). На второй стадии происходят следующие процессы: 1) деполимеризация олигомеров до мономеров; 2) гидрирование мономерных фенолов в оксо- и алкилпроизводные циклогексана; 3) образование газовых продуктов (преимущественно метана, 95 об. %) вследствие каталитического гидрокрекинга растворителя. Depolymerization of hydrolysis lignin in supercritical n-hexane medium was carried out in two stages: 1) lignin treatment in an autoclave at 250°C and 15 MPa; 2) hydrogenation of the solution obtained in the first stage at 250°C and 9 MPa on a Ru/C catalyst. The products of the first and second stages were analyzed by HPLC, GPC, gas chromatography, chromatography-mass spectrometry, and elemental analysis. At the first stage, the degree of depolymerization was 17 %, the mono- and oligomeric fragments of lignin that passed into solution as a result of depolymerization have an MMD from 65 Da to 270 kDa. Monomer composition of the solution: mono-, di-, tri- and tetraalkyl derivatives of benzene (2.8 wt. %), guaiacol and its alkyl derivatives (0.6 wt. %), including coniferyl alcohol (0.06 wt. %). At the second stage of transformation the following processes occur: 1) depolymerization of oligomers to monomers; 2) hydrogenation of monomeric phenols to derivatives of cyclohexane and its oxo derivatives; 3) formation of gas products, mainly methane (95 vol. %), as a result of hydrocracking of the solvent.

Conversion of isopropanol under supercritical conditions (400 °C, 11.0 MPa) on calcium and magnesium stannates MSnO3 (M = Ca, Mg) was studied. The main direction of the process is dehydrogenation of isopropanol to acetone, which then enters into the aldol condensation with selective formation of isomeric mesityl oxides. Products of hydrogenation of the C=C and C=0 bonds in mesityl oxide as well as products of isopropanol dehydration were also obtained. Under the experimental conditions, isopropanol is both a supercritical solvent and a source of hydrogen for hydrogenation of the multiple bonds. According to the results of diffuse reflectance infrared Fourier transform spectroscopy study using deuterated chloroform as a probe molecule, basic oxygen sites of the catalysts are of medium strength. During the conversion of isopropanol the more active catalyst MgSnO3 completely decomposes into the oxides MgO and SnO2 and the latter is then reduced to metallic tin, while the less active catalyst CaSnO3 is reduced slightly.

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 results of a study of tandem reactions - aldol-crotonic condensation and hydrogenation by the mechanism of hydride transfer in acetone-isopropanol mixtures on a МgSnО3 catalyst at 300–400°C and 12.0 MРa are presented. In these conditions the mixture of reactants (acetone and isopropanol) and reaction products is in supercritical state. The temperature dependences of the reactants conversion and the selectivity for condensation and hydrogenation products are considered. It has been established that the hydrogenation of acetone aldol-crotonic condensation products proceeds by the addition of hydrogen from isopropanol molecule to C=O-bonds of isomeric mesityl and phorone oxides and is accompanied by dehydration of alcohols and isomerization of double C=C-bonds. The optimal conditions for the formation of the carbonyl group hydrogenation products are 350°C and the ratio acetone : isopropanol = 7 : 3. At the acetone to isopropanol ratio 1 : 1, methylpentadienes dominate in the products of mesityl oxide conversion. The hydrogenation reaction also proceeds with the participation of isophorones, the condensation products of three acetone molecules.

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 aldol condensation of acetone under supercritical conditions at 300–400°C and 11.0 MPa was carried out on BaSnO3-450 and BaSnO3-750 catalysts prepared by calcination of BaSn(OH)6 at 450 and 750°C, respectively. Conducting the reaction under these conditions makes it possible to overcome the problem of catalyst deactivation by coking and to obtain valuable chemicals with high selectivity. At 300°C, both catalysts provide selectivity of 85–87

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 reduction of carbon dioxide with molecular hydrogen in the presence of Fe,Cr-containing catalysts supported on a Sibunit carbon material at 400°C and pressures of 0.1 and 8.5 MPa is studied. Carbon monoxide can selectively form over the catalysts with an Fe : Cr ratio of 1 : 5. C1–C4 hydrocarbons with a predominance of methane are produced together with CO upon a decrease in the content of chromium (5Fe–0.25Cr/C sample). Transmission electron microscopy shows that the 5Fe–5Cr/C catalyst contains iron chromite FeCr2O4 (spinel structural type) as the main phase preventing the reduction of iron and the formation of iron carbides, which, in turn, provide the formation of hydrocarbons in the reaction of CO2 and H2.

Представлены результаты исследования тандемных реакций - альдольно-крото­новой конденсации и гидрирования по механизму гидридного переноса в смеси ацетон-изопропанол на катализаторе МgSnО3 при 300-400 °С и 12,0 МПа. При этих условиях смесь субстратов и продуктов реакции находится в сверхкритиче­ском состоянии. Рассмотрены зависимости от температуры степени превращения реагентов (ацетона и изопропанола) и селективности по продуктам конденсации и гидрирования. Установлено, что гидрирование продуктов альдольно-кротоновой конденсации ацетона протекает путем присоединения водорода от молекул изопропанола по С=О-связям изомерных оксидов мезитила и форонов и сопровож­дается реакциями дегидратации спиртов и изомеризации двойной С=С-связи. Оптимальные условия образования продуктов гидрирования карбонильной груп­пы - 350 °С и соотношение ацетон: изопропанол = 7 : 3. При соотношении ацетон: изопропанол = 1 : 1 в продуктах превращения оксида мезитила преоблада­ют метилпентадиены. Реакция гидрирования протекает также с участием изофо­ронов - продуктов конденсации трех молекул ацетона. The results of a study of tandem reactions - aldol-crotonic condensation and hydrogenation by the mechanism of hydride transfer in acetone-isopropanol mixtures on a МgSnО3 catalyst at 300-400 °C and 12.0 MРa are presented. In these conditions the mixture ofreactants (acetone and isopropanol) and reaction products is in the supercritical state. The temperature dependences of the reactants conversion and the selectivity for condensation and hydrogenation products are considered. It has been established that the hydrogenation of the acetone aldol-crotonic condensation products proceeds by the addition of hydrogen from isopropanol molecule to the C=O-bonds of isomeric mesityl and phorone oxides and is accompanied by the dehydration of alcohols and the isomeriza­tion of double C=C-bonds. The optimal conditions for the formation of the carbonyl group hydrogenation products are 350°C and the ratio acetone : isopropanol = 7 : 3. At the acetone to isopropanol ratio 1 : 1, methylpentadienes dominate in the products of mesityl oxide conversion.The hydrogenation reaction also proceeds with the participation of isophorones, the condensation products of three acetone molecules.

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.

The activity of Pt/C, Pt/Ni/C, Pt/Cr/C, and Pt-Ni-Cr/C catalysts in the dehydrogenation reaction of bicyclohexyl, a step of hydrogen release in chemical hydrogen storage systems, was studied. The catalyst surface structure was investigated by transmission electron microscopy. The charge state of platinum was assessed by XPS. The role of nickel and chromium promoters in the formation of electron-deficient (Pt δ+ ) and zero-valent (Pt 0 ) platinum was analyzed. The activity of catalysts in the dehydrogenation reaction of bicyclohexyl was affected by the Pt δ+ /Pt 0 ratio. The highest conversion and yield of biphenyl, the product of the complete dehydrogenation of bicyclohexyl, were achieved at aPt δ+ /Pt 0 ratio close to 1–2.

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

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.

Изучена альдольная конденсация ацетона на станнате стронция при температуре 250-400 °С и давлении 2,5 и 12,5 МПа, где основными продуктами являлись оксид мезитила и изофорон. Показана высокая стабильность, а также производительность катализатора SrSnO в сверхкритических условиях, которая по изомерам оксида мезитила при 350 °С и 12,5 МПа достигала более высоких значений по сравнению с газовой фазой и составляла 9 г • ч • г. Aldol condensation of acetone on strontium stannate isstudied at a temperature of 250- 400 °C and a pressure of 2.5 and 12.5 MPa. The main reaction products are mesityl oxide and isophorone. It is shown that the SrSnO catalyst is stable under supercritical conditions and its productivity with respect to mesityl oxide isomers at 350 °C and 12.5 MPa equals 9 g • hgcat which is higher than in the gas phase.