G. I. Lin

Fundamentals of Methanol Synthesis and Decomposition

Fundamental studies of methanol synthesis and decomposition (mainly over Cu-based catalysts) have been carried out. Various kinetic approaches, i.e. TPD study after various chemical treatments of catalyst, non-steady-state transformation of strongly adsorbed species, tracer technique, and steady-state kinetics, have been used. The macroscopic mechanism and detailed reaction scheme of methanol synthesis, as well as the kinetic description of the process have been established and proven. Methanol synthesis over Cu-based catalysts was found to occur by CO2 hydrogenation only, which was coupled with the water-gas shift reaction.Methanol decomposition and steam reforming over Cu-based catalysts have been studied. It was shown that methanol decomposed into a mixture of CO and H2 via methyl formate as an intermediate. Methanol transformation into the mixture of CO2 and H2 occurred by interaction of methanol and water. The reaction proceeded as the reverse methanol synthesis reaction, accompanied by the reverse water-gas shift reaction.

Synthesis of Gasoline from Syngas via Dimethyl Ether

Zeolite H-TsVM has been loaded with palladium by different methods. The properties of the resulting catalysts in gasoline synthesis from syngas via dimethyl ether depend on the way in which palladium was introduced. The catalysts have been characterized by ammonia temperature-programmed desorption (TPD), temperature-programmed reaction with hydrogen, and X-ray photoelectron spectroscopy. According to ammonia TPD data, use of a palladium ammine complex instead of palladium chloride reduces the concentration of strong acid sites and raises the concentration of medium-strength acid sites, thereby reducing the yield of C1–C4 hydrocarbons and increasing the yield of gasoline hydrocarbons. At T = 340°C, P = 100 atm, and GHSV = 2000 h−1, the dimethyl ether conversion is 98–99%, the gasoline selectivity is >60%, the isoparaffin content of the product is ∼61%, and the arene content is not higher than 29%.

Properties of surface compounds in methanol conversion on γ-Al2O3: Data of in situ IR spectroscopy

In situ IR spectroscopic studies show that a formate, an aldehyde-like complex, and bridging and linear methoxy groups exist on the alumina surface involved in methanol conversion. In the absence of methanol in the gas phase, the interaction between two bridging methoxy groups yields dimethyl ether in the gas phase. When methanol is present in the gas phase, it interacts with methoxy groups on the surface. This reaction makes the main contribution to the formation of dimethyl ether. The linear methoxy group undergoes conversion via several routes. The main route is desorption with methanol formation in the gas phase, and no more than 10% of the linear methoxy groups are converted into formate and aldehyde, which are CO2 sources in the gas phase. In the absence of methanol in the gas phase, the conversion rate of the methoxy groups is independent of the presence of water and oxygen. A scheme of the surface reactions is suggested to explain the conversion of the methoxy groups.

Laws of selective CO oxidation over a Ru/Al2O3 catalyst in the surface ignition regime: II. Transition states

The kinetics of selective CO oxidation (or individual CO or H2 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 gCat−1 h−1 and reagent percentages of ∼1 vol % CO, ∼1 vol % O2, ∼60 vol % H2, and N2 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 H2 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.

Spectroscopic study of the properties of surface compounds in methanol conversions on Cu/γ-Al2O3

The reactions of methanol on the (10% Cu)/γ-Al2O3 surface were studied by the spectrokinetic method (simultaneous measurements of the conversion rates of surface compounds and the product formation rates). Bridging and linear methoxy groups result from the interaction of methanol with surface hydroxyl groups. Formate and aldehyde-like complexes form by the oxidative conversion of the linear methoxy groups. Hydrogen forms via the recombination of hydrogen atoms on copper clusters, and the hydrogen atoms result from interconversions of surface compounds. The source of CO2 in the gas phase is the formate complex, and the source of CO is the aldehyde complex. In the absence of methanol in the gas phase, dimethyl ether forms by the interaction between two bridging methoxy groups. When present in the gas phase, methanol reacts with methoxy groups on the surface. The roles of oxygen and water vapor in the conversions of surface compounds are discussed.

Selective CO oxidation on a Ru/Al2O3 catalyst in the surface ignition regime: 1. Fine purification of hydrogen-containing gases

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.

The study of formation of supports and catalysts based upon Al2O3/Al cermets

The regularities of formation of porous metalloceramic supports and catalysts of a A/Al2O3/Al type via hydrothermal oxidation of powdered aluminum in mixture with various dispersed additives (A) have been investigated. The interrelation between the parameters of composites synthesis (temperature and time of processing, type of the aluminum powder and nature of additives) and their properties including phase composition, texture, mechanical and catalytic properties (CO and butane oxidation, methane steam reforming, Fischer-Tropsch synthesis) was analyzed.

Temperature-programmed surface reactions of methanol on commercial Cu-containing catalysts

Temperature-programmed reaction spectroscopic studies reveal two main transformation routes of methanol adsorbed on commercial Cu-containing catalysts. First the reverse methanol synthesis reaction (hydrolysis) CH3OH+H2O=CO3+3H2; a second route is not connected with CH3OH synthesis and it includes bimolecular interaction of methanol giving methyl formate. The conversion of the latter compound results in the formation of CO, and other intermediates often postulated in methanol synthesis.

Synthesis of methanol on Cu-based catalyst: Kinetic model

Kinetic experimental and theoretical studies of methanol synthesis on a copper-containing SNM-3 oxide catalyst have been carried out to discriminate between kinetic models. A kinetic model describing methanol synthesis from carbon oxides and hydrogen fairly well in a wide range of gas mixture compositions and temperatures at P=5–10 MPa, is defined.AbstractПроведено экспериментальное и теоретическое исследование кинетики синтеза метанола на окисном медьсодержащем катализаторе СНМ-3. Проведена дискриминация кинетических моделей. Определена кинетическая модель, удовлетворительно описывающая процесс синтеза метанола из оксидов углерода и водорода в широкой области составов газовой смеси при давлениях 5–10 МПа.

Surface reactions of dimethyl ether on γ-Al2O3: 1. Adsorption and thermal effects

Reactions of dimethyl ether (DME) over γ-Al2O3 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-Al2O3 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.