A. Ya. Rozovskii

Monolith perovskite catalysts of honeycomb structure for fuel combustion

New method of dispersed perovskites synthesis based upon mechanochemical activation of the solid starting compounds is elaborated. The influence of defect structure of these compounds as well as surface segregation on their catalytic properties is discussed. Basic stages of the monolith perovskite catalysts preparation are optimized. The experimental samples of monolith catalysts of various shapes are obtained, possessing high activity, thermal stability and resistance to catalytic poisons.

A role of surface nitrite and nitrate complexes in NOx selective catalytic reduction by hydrocarbons under oxygen excess

NO adsorption over three types of catalytic systems, such as cation-exchanged zeolites, transition metal oxides supported on γ-Al2O3, and partially stabilised tetragonal ZrO2 (PSZ) was studied by using the TPD method. NO forms several surface complexes having different desorption temperatures. TPD results compared with catalytic properties of these systems in the selective reduction of NOx by propane under oxygen excess showed that strongly bound nitrites and nitrates appeared to be true intermediates in this reaction.

The reaction mechanism of selective catalytic reduction of nitrogen oxides by hydrocarbons in excess oxygen: Intermediates, their reactivity, and routes of transformation

The main features of the mechanism of selective reduction of nitrogen oxides by hydrocarbons (methane, propane, and propylene) in excess oxygen catalyzed by systems containing transition metal cations are considered. A combination of steady-state and non-steady-state kinetic studies, in situ Fourier-transform infrared (FTIR) spectroscopy, temperature-programmed desorption, and theoretical analysis of bond strengths and spectral data for adsorption complexes made it possible to determine reliably that surface nitrate complexes are key intermediates at real temperatures of catalysis. The rate-limiting step in these reactions includes the interaction of these complexes with hydrocarbons or their activated forms. Factors are considered that determine the structure, bond strength, and routes of nitrate complexes transformations under the action of hydrocarbons. Mechanistic schemes are proposed for the reaction of various types of hydrocarbons in which the determining role belongs to the formation of organic nitro compounds in a rate-limiting step. Their further fast transformation with the participation of surface acid sites resulting in the formation of ammonia, which is a highly efficient reducing agent, though not limiting the whole process, but determines nevertheless both the selectivity to the target product, molecular nitrogen, and the selectivity of hydrocarbon consumption for nitrogen oxide reduction.

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.

Mechanism and Kinetics of Reactions of C1 Molecules on Cu-Based Catalysts

The mechanism and kinetics of reactions occurring in the course of natural gas processing into motor fuels and other chemical products are considered with emphasis on copper-based catalysts. The following reactions are considered: methanol and methyl formate syntheses, dimethyl ether synthesis from syngas and by methanol dehydration, water-gas shift reaction, steam reforming of methanol and its decomposition to produce syngas, and others. It is shown that a key role in the mechanisms of the above reactions belong to transformations of stable, strongly (“irreversibly”) chemisorbed species, and this fact determines the specific features of the schemes of their mechanisms and kinetic models. The use of the specific features of reaction mechanisms makes it possible to increase the process efficiency (methanol and dimethyl ether syntheses) and provide a high selectivity (methyl formate synthesis).

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.