Josef Tichý

Reducibility and oxidation activity of Cu ions in zeolites: Effect of Cu ion coordination and zeolite framework composition

Reducibility and catalytic activity in propane oxidation was studied for the Cu ions exchanged in zeolites of structural types ZSM-5 (MFI), ferrierite (FER) and erionite (ERI) with different Cu/Al/Si compositions, and Na+ or H+ ions present as co-cations. The Cu ions were exchanged at conditions of various Cu concentrations in salt solutions, anion type and pH to receive samples with different Cu ion structures. Reducibility of the Cu ions in zeolites has been investigated by means of temperature-programmed reduction by hydrogen, and zeolite evacuation and treatment in CO atmosphere with subsequent detection of the Cu+–(CO)n complexes by IR spectroscopy. Redox properties of the Cu ions, represented by their reducibility and catalytic activity in propane oxidation to CO and CO2, dramatically differed depending on Cu loading in the zeolite, content of aluminum in the framework and presence of co-cations (Na+ versus H+ ions), as well as on the state of the Cu ions, i.e. if atomically dispersed as exchanged cations or present in CuO oxidic-like species. These results have been compared with our previous studies revealing several defined Cu ion sites characteristic for high-silica zeolites, differing in coordination-siting, positive charges, and population depending on Cu loading, and content of Al in the framework. It has been shown that, well-dispersed CuO species exhibit much higher oxidation activity and reducibility compared to the exchanged Cu ions. The redox properties of the exchanged Cu ions have been found to be highly controlled, besides the local geometry of the ligand field, by the total delocalized negative framework charge, given by the Al content in the framework, and the local negative charge adjacent to the cation, controlled by the Si–Al sequences. The Cu ions balanced by a single AlO2− entity, being most populated in zeolites with high Cu loading and in zeolites with low concentration of aluminum in the framework are suggested to be those easily reducible, and exhibiting high oxidation activity.

Oxidation of acrolein to acrylic acid over vanadium-molybdenum oxide catalysts

Abstract The present paper summarizes basic result of theoretical research into catalytic gas-phase oxidation of acrolein to acrylic acid on vanadium-molybdenum oxide catalyst. It presents findings concerning the optimum way of preparation of the catalysts and their characteristics inclusive of determination of the active component. The second part deals with evaluation of results of mechanistic studies of the oxidation, i.e. identification of the individual transition complexes as well as evaluation of effects of the individual reaction components on the oxidation course. Moreover, it presents the results of experimental studies of the reaction kinetics and discusses the possibility of controlling of catalytic properties of the catalysts. The basic research was carried out in two institutions, namely Institute of Catalysis of the Siberian Branch of the Russian Academy of Sciences and the University of Pardubice, which were cooperating for a period of time.

Mechanism of selective oxidation of methanol over stannic oxide-molybdenum oxide catalyst

The mechanism of the selective oxidation of methanol on Sn-Mo oxide catalyst with molar ratio Mo/(Mo + Sn) = 0.3 is investigated. The interaction of methanol and its oxidation products (i.e. formaldehyde and methyl formate) is studied by FT-IR spectroscopy. The data are interpreted on the basis of a reaction mechanism which contains 10 elementary steps. The behaviors of the surface species (methoxy, formate and dioxymethylene groups) are compared with those monitored on other systems and the catalyst requirements for the title reaction are discussed.

Catalytic oxidation of isobutyraldehyde over a molybdenum-vanadium oxide catalyst

The effect of composition of reaction mixture on the gas-phase oxidation of isobutyraldehyde has been studied over a Mo−V oxide catalyst supported on Aerosil. It was found that oxygen, in contrast to water vapor, markedly changes the conversion of isobutyraldehyde and yields of acetone and methacrolein.

ACID-BASE PROPERTIES OF SN-MO-OX CATALYSTS

The acidity and basicity of Sn−Mo−Ox catalysts with different Mo/Mo+Sn atomic ratios were measured by determining the adsorption isotherms of pyridine and acetic acid by chromatographic method. It was found that acidity and basicity go through a maximum at a Mo content of 15–20 at.%.AbstractИзмеряли кислотность и основность катализаторов Sn−Mo−Ox с различным атомным соотношением Mo/Mo+Sn, определяя адсорбционные изотермы пиридина и уксусной кислоты хроматографическим методом. Кривые кислотностн и основности имеют максимум при содержании Mo=15–20 at.%.

CATALYTIC OXIDATION OF PROPYLENE TO ACROLEIN ON A MULTICOMPONENT OXIDE CATALYST

Rate equations have been found and reaction schemes for oxidation of propylene to acrolein and acrylic acid have been suggested.AbstractНайдены скороттные уравнения и предложены соответствующие схемы окисления пропилена в акролеин и в акриловую кислоту.

Sorption of Acetic and Propionic Acids and Propanal on a Molybdenum-Vanadium Oxide Catalyst

It has been found by gas chromatography that the equilibrium adsorption of propanal, propionic and acetic acids on molybdenum-vanadium oxide catalyst can be described by the Langmuir adsorption isotherm. The existence of carboxylates on the catalyst surface has been proved by IR spectroscopy.