The physicochemical and catalytic (CO2 hydrogenation) characteristics of Mo-containing catalysts were studied. The catalysts containing 8 and 15 wt

The physicochemical and catalytic (CO₂ hydrogenation) characteristics of Mo-containing catalysts have been studied. Catalysts with an oxide content of Mo 8 and 15 wt% were prepared by impregnation with ammonium paramolybdate γ-Al₂O₃ followed by drying and calcining at 500°C. The introduction of Mo oxide reduces the pore volume of the support and increases their average size, which indicates the distribution of the deposited molybdenum oxide in the pores of the support. According to X-ray diffraction data, the calcined catalyst contains practically no crystalline MoO₃ phase. According to the Raman spectra, oxygen-containing formations are present on the catalyst surface, in which Mo atoms are tetrahedrally and octahedrally coordinated with respect to oxygen atoms. The impregnated MoO₃ oxide is partially reduced by hydrogen during linear heating starting from 320°C. Hydrogenation of CO₂ (gas of composition, vol.%: 30.7 CO₂, 68 H₂, rest. N2, sample 0.5 g) was studied in the mode of linear heating up to 400°C. The main reaction is the reverse reaction of CO steam reforming. The contribution of the methanation reaction to CO₂ hydrogenation is small. An increase in temperature and pressure has a positive effect on CO₂ conversion. With an increase in pressure from 1 to 5 MPa, the CO content increases approximately twofold. In the hydrogenation of CO₂, γ-Al₂O₃, preheated in a flow of H₂ to 400°C, also exhibits noticeable activity, although significantly lower compared to Mo-containing catalysts. With increasing pressure, the activity of aluminium oxide and Mo-containing catalysts, increases.

A ZnO/Al2O3 catalyst synthesized by impregnating gamma-alumina from a zinc nitrate solution and calcination at 400°C is studied in the hydrogenation of carbon oxides. During heating in a stream of a 2.4% H2/N2 mixture to 400°С, ZnO undergoes partial reduction. The activity of the reduced catalyst is studied in a range of 300–400°С at 5 MPa and a space velocity of 6000 NL $${\text{kg}}_{{{\text{cat}}}}^{{ - 1}}$$ h−1. The main product of CO hydrogenation is methanol. In addition, the methanol dehydration and CO methanation reactions occur. Water formed during methanol dehydration provides the formation of CO2 via the CO steam reforming reaction. With an increase in temperature from 300 to 400°C, the selectivity for oxygenates (methanol and dimethyl ether, in terms of methanol) decreases from ~74 to 56%, while the selectivity for hydrocarbons (methane, ethane, ethylene, propane) increases from 1 to 14%. The main products of CO2 hydrogenation are CO and H2O. The formation of oxygenates and a small amount of methane, in addition to CO, is observed. Water formed in a significant amount during CO2 hydrogenation adversely affects the dehydration of methanol. In methanol synthesis at 240°C, the catalyst exhibits an insignificant activity in the case of using H2/CO and almost no activity in the case of H2/CO2. Data on CO and CO2 hydrogenation in the presence of ZnO/Al2O3 are consistent with the results for precipitated ZnO. In addition, at a pressure of 3 or 5 MPa and a temperature of 344 or 364°C, the content of oxygenates in the case of CO hydrogenation is 4–5 times higher than that in the case of CO2 hydrogenation. Analysis of the dependence of the relative selectivity for oxygenates on the contact time leads to the conclusion that, in the presence of zinc oxide, methanol is formed from both CO and CO2.

In the context of utilization of carbon dioxide emissions, a study of the CO2 conversion to methanol and dimethyl ether (DME) under flowcirculation conditions, when a part of converted gas returns to the reactor, was carried out. Experimental data on the synthesis of methanol (commercial catalyst Megamax 507) and direct synthesis of DME (Megamax 507/commercial zeolite ZVM, weight ratio 1/1) are reported. In the methanol synthesis from syngas, vol.%: H2 – 76.6, CO2 – 19.8, N2 – 3.6 performed at 240–260 °C and pressure 5.3 MPa, a high conversion of CO2 was reached: 84–99.6% at a low selectivity of the side reaction (CO synthesis, not higher than 4.7 %). The maximum specific yield of methanol at 260 °C was 1.24 kg(kgcat·h)–1. Special-purpose experiments demonstrated that the methanol synthesis is accompanied by a small heating (up to 10 °C) at the catalyst bed inlet, which testifies to polytropicity of the reactor. In the synthesis of DME, the DME yield referred to bifunctional catalyst was within 0.16–0.33 kg(kgcat·h)–1 depending on the conditions. Therewith, the conversion of methanol to DME was not lower than 42 %, the conversion of CO2 was within 79–96 %, and the DME synthesis proceeded under nearly isothermal conditions.

We developed an original gas chromatographic procedure for determining the products and reagents for the catalytic synthesis of dimethyl ether (DME) from synthesis gas, which enables the simultaneous detection of СН 3 ОН, DME, СО, СО 2 , Н 2 , Н 2 О, N 2 , and hydrocarbons to С 6 . The gas circuit includes four detectors, three packed columns, two precolumns (to prevent water and organic compounds from entering molecular sieve columns) in combination with two relief valves and two pressure regulators for the implementation of the back purging of precolumns. The system is assembled based on a Khromatek-Kristall 5000 chromatograph. The determination is carried out at a constant temperature of 140°C. The duration of analysis is not more than 12 min. Because of the presence of a flame ionization detector, it is possible to detect trace amounts of hydrocarbons, as well as ethane in the presence of large amounts of CO 2 .

The kinetics of the direct synthesis of dimethyl ether (DME) from synthesis gas (21.8 vol % CO, 5.2 vol % CO 2 , 5.3 vol % N 2 , and 67.7 vol % H 2 ) is studied under laboratory flow reactors in a pressure range of 0.2–5 MPa in the presence of a bifunctional catalyst. The bifunctional catalyst is synthesized by pelletizing a mixture of appropriate fractions of the following milled commercial components: a Megamax 507 methanol catalyst and γ -alumina with a graphite additive. Data on the activation of the bifunctional catalyst are consistent with the TPR data for the original Megamax 507 sample, suggesting that the synthesis conditions for the bifunctional catalyst do not affect the state of copper oxide. At temperatures of up to 280°C, a space velocity of about 4000–10000 L/(kg cat h), and a pressure of 3–5 MPa, the productivity with respect to oxygenates (DME and methanol) grows linearly along with the load. An increase in load results in a limiting value that can be used to determine the maximum oxygenate productivity of the catalyst as a function of temperature and pressure. A set of experimental data on the effect of space velocity, temperature, and pressure on the composition of the converted gas and the DME/methanol ratio is derived.

A laboratory flow setup loaded with a bifunctional catalyst was used for kinetic studies of the direct synthesis of dimethyl ether (DME) from synthesis gas (21.8 vol % CO, 5.2 vol % CO 2 , 5.3 vol % N 2 , rest H 2 ) at the pressure range of 0.2–5 MPa. The bifunctional catalyst was prepared by tabletting a mixture of milled fractions of industrial components: methanol catalyst Megamax 507 and γ-alumina with a graphite additive. The data on the activation of the bifunctional catalyst agree with the TPR data of the initial Megamas 507 that indicates no influence of the catalyst preparation conditions on the copper oxide state. The oxygenate (DME and methanol) production rate increases linearly with increasing load at temperature up to 280 °C and flow rate up to 4000–10000 L/(kgcat·h) at pressure of 3 to 5 MPa. An increase in load leads to reaching the limit value that allows the estimation of the maximal oxygenate production rate of the catalyst depending on temperature and pressure. A series of experimental data on the influence of flow rate, temperature, and pressure on the composition of the converted gas and on the DME/methanol ratio are reported.

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al2O3) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.

Reactions of dimethyl ether (DME) over γ-Al 2 O 3 at 250°C have been investigated in a flow catalytic reactor. The main products of the interaction between DME and alumina are methanol and water. Heat evolution is observed as DME is passed over alumina, and replacing DME with nitrogen gives way to heat absorption. Calcination of alumina before the reaction considerably strengthens the exotherm, which is due to DME adsorption, while the endotherm is due to the desorption of weakly bound DME. The role of the hydroxyl groups of γ-Al 2 O 3 in methanol and water formation has been elucidated. Treating alumina with water vapor after bringing it into contact with DME completely restores the hydroxyl cover and replaces strongly adsorbed DME with hydroxyl groups.

A procedure was developed for evaluating the adsorption of hydrocarbons on solids by monitoring the temperature of the gas over the sample layer and inside it, the heat conductivity of the gas at the inlet and outlet of the flow reactor, and the composition of the gas after the sample. The adsorption-desorption of isobutane accompanied by heat liberation or absorption (recorded as a temperature change in the zeolite layer) was studied using the H-TsVM zeolite as an example. The temperature effects during isobutane adsorption and desorption were compared. It was concluded that below ∼90°C, some part of isobutane is significantly chemisorbed on H-TsVM. The highly adsorbed isobutane can be removed by keeping the sample in a nitrogen flow for a long time or by heating it above 90°C. Time dependence of isobutane desorption at constant temperature can be described by first order kinetic equation, making possible to estimate the activation energy of desorption of highly chemisorbed isobutane using the data on thermodesorption at linear temperature increase.

Разработана методика оценки адсорбции углеводородов на твердых образцах, основанная на мониторинге температуры газа над слоем и в слое образца, теплопроводности газа на входе и выходе из проточного реактора, состава газа после образца. На примере цеолита Н-ЦВМ изучена адсорбция – десорбция изобутана, сопровождающаяся выделением – поглощением тепла, что фиксируется по изменению температуры в слое цеолита. На основании сопоставления данных по величине температурного эффекта при адсорбции и десорбции изобутана сделан вывод о том, что при температурах адсорбции ниже 90° часть изобутана прочно хемосорбируется на цеолите Н-ЦВМ. Установлено, что удаление прочно адсорбированного изобутана может быть проведено только при длительной выдержке в токе азота или при нагреве выше 90°С. Временная зависимость десорбции изобутана при постоянной температуре описывается кинетикой первого порядка по величине покрытия, что позволило оценить энергию активации десорбции прочно хемосорбированного изобутана по данным термодесорбции в линейном нагреве. Временная зависимость десорбции изобутана при постоянной температуре описывается кинетикой первого порядка по величине покрытия, что позволило оценить энергию активации десорбции прочно хемосорбированного изобутана по данным термодесорбции в линейном нагреве.

The specifics of CO hydrogenation over a 5%Ru/Al2O3 catalyst in a flow reactor at a pressure of 1.5 MPa has been considered. The feed gas mixture has been composed of (vol %) 30.5 CO, 2.3 CO2, 65 H2, and N2 as the rest. The CO methanation reaction readily passes to the external-diffusion regime—catalyst surface ignition (CSI) mode—either by heating the catalyst in the reaction medium or by replacing H2 with the reactant gas having a temperature above the critical ignition temperature. On passing to the CSI mode, the temperature at the entrance to the catalyst bed and the methane content at the reactor outlet abruptly increase, the yield of CO2 produced via the water-gas shift reaction increases, and the CO content drops to zero. Under the CSI regime, temperature oscillations with a period of 3–5 min and an amplitude of ∼3°C are observed, which are sustained during catalyst cooling until the extinction of the reaction. A comparison of the product compositions at the reactor outlet in the cases of the “thick” (20 mm) and “thin”(3 mm) catalyst bed has shown that the reverse water-gas shift, an endothermic reaction, occurs in lower, colder layers of the thick bed. As a result, the extinction of the reaction is faster in the thick than in the thin bed. Methanation of CO is accompanied by the Fischer-Tropsch reaction: a variety of carbon compounds are formed with their yield being decreased on passing to the CSI mode.

The vapor phase dehydration of methanol to dimethyl ether using catalytic membrane reactor was studied for the first time. The catalytic membranes were prepared by the deposition of a solid-acid catalyst, namely, F-4SF resin (the Russian analog of Nafion™), onto the internal surface of the ceramic ultrafiltration tubular membrane. The catalytic membrane reactor was used in three different configurations of feed supply and product withdrawal. Among these three configurations, the flow through catalytic membrane reactor demonstrates the maximum methanol conversion of 36.4% and 100% selectivity toward DME.

The peculiarities of methanol transformation on the surface of perfluorinated copolymer, fluoroplastic, containing sulfo groups were studied. At temperatures of 70–120°C, the polymer was established to have high initial activity during the conversion of methanol into dimethyl ether; this reaction was, however, accompanied by strong water sorption that leads to a rapid drop in the activity. The sorption/desorption processes were characterized by temperature effects such as heating during sorption and cooling during desorption. The structure of the polymer in the salt (sodium cations) and acid (hydrolyzed polymer) forms was studied by IR spectroscopy. H 3 O + SO 3 − ionic pairs were found to be present in the acid form.

The kinetics of selective CO oxidation (or individual CO or H 2 oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 g Cat −1 h −1 and reagent percentages of ∼1 vol % CO, ∼1 vol % O 2 , ∼60 vol % H 2 , and N 2 to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H 2 oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.

Selective CO oxidation in a mixture simulating the methanol steam reforming product with an air admixture was studied over Ru/Al2O3 catalysts in a quasi-adiabatic reactor. On-line monitoring of the gas temperature in the catalyst bed and of the residual CO concentration at different reaction conditions made it possible to observe the ignition and quenching of the catalyst surface, including transitional regimes. A sharp decrease in the residual CO concentration takes place when the reaction passes to the ignition regime. The evolution of the temperature distribution in the catalyst bed in the ignition regime and the specific features of the steady-state and transitional regimes are considered, including the effect of the sample history. In selective CO oxidation and in H2 oxidation in the absence of CO, the catalyst is deactivated slowly because of ruthenium oxidation. In both reactions, the deactivated catalyst can be reactivated by short-term treatment with hydrogen. A 0.1% Ru/Al2O3 catalyst is suggested. In the surface ignition regime, this catalyst can reduce the residual CO concentration from 0.8 vol % to 10–15 ppm at O2/CO = 1 even in the presence of H2O and CO2 (up to ∼20 vol %) at a volumetric flow rate of ∼100 1 (g Cat)−1 h−1, which is one magnitude higher than the flow rates reported for this process in the literature.