V. V. Kharlamov

Tracer studies of acid-base catalyzed reactions: XIII. The isomerization of the n-butenes over zinc oxide and alumina☆

Abstract The isomerization of n -butenes was studied over zinc oxide in a glass recirculation system. Experiments were made with each of the pure isomers at temperatures between 0 and 90 °C. At low temperatures and conversions the reactions were all zero order in olefin. Below 50 °C the Arrhenius plots were linear so that the reaction coordinates of the system could be mapped. At 90 °C, the reaction was no longer zero order. These results indicated that the reaction occurred in the nonlinear part of the adsorption isotherm. Tracer experiments using cis -2-butene-2,3 d 2 showed that cis -2-butene can be converted directly into the trans - isomer (without going through 1-butene as an intermediate). At higher temperatures both the kinetic data and the tracer results were complicated by secondary processes. The tracer studies of these reactions were also carried out over a γ-alumina catalyst. Experiments were made using cis -2-butene-2,3 d 2 and cis -2-butene- d 8 as well as binary mixtures of these compounds. In contrast with ZnO, intermolecular exchange was important over alumina, particularly in the 1-butene product. CO 2 , which is a good poison for olefin-D 2 exchange, was not nearly as effective for intermolecular exchange. Moreover, the alumina OH groups contributed to the intermolecular exchange under the reaction conditions. ZnO behaved as an “ideal system” in which the kinetic and tracer data were entirely consistent with the previous ir studies (Dent A. L., and Kokes, R. J., J. Phys. Chem. 75 , 487, 1971; Chang, C. C., Conner, W. C., Jr., and Kokes, R. J., J. Phys. Chem. 77 , 1957, 1973) of the intermediate species. Although on alumina the picture was obscured by simultaneous exchange processes, comparison of the present results with other published data led to the conclusion that, the mechanisms for n -butene isomerization over ZnO and alumina are the same or very similar at temperatures below 100 °C.

Vapor phase oxidation of methylpyridines on zeolite catalysts

It has been established that zeolites containing Pd and Cu ions catalyze the vapor phase oxidation of methylpyridines. In oxidation of 2-methylpyridine on PdCuNa-mordenite at 375 °C the yield of 2-pyridinecarbaldehyde is 40 % of its theoretical values.AbstractУстановлено, что цеолиты, содержащие ионы Pd и Cu, являются катализаторами парофазного окисления метилпиридинов. При окислении 2-метилпиридина на PdCuNa-мордените выход 2-пиридинкарбальдегида при 375°C составляет 40% от теории.

Catalytic properties of synthetic mordenite in the isomerization, hydrogenation, and hydroisomerization of certain hydrocarbons

1. The catalytic properties of synthetic mordenite in the isomerization of n-pentane and cyclohexane, and the hydrogenation and hydroisomerization of benzene in the presence of hydrogen were investigated. 2. The hydrogen form of mordenite is an active catalyst of the isomerization of saturated hydrocarbons, while the introduction of palladium and nickel into the H-form of mordenite does not increase the activity of the catalyst. 3. The sodium-form of mordenite is an active catalyst of the hydrogenation of benzene.

Hydrogenation of cyclohexene on different types of catalysts

Hydrogenation of cyclohexene has been studied under pressure in a flow reactor on the following catalysts: Na- and H-forms of Y-type zeolites, erionite, magnesium and lanthanum oxides, palladium on silica and aluminum oxide. This reaction is accompanied by skeletal isomerization to give methylcyclopentane and methylcyclopentenes. The differences in activation energies for isomerization and hydrogenation reactions were estimated as 83–96 kJ/mole for NaY and Na,K-erionite, 33–50 kJ/mole for the H-forms of the zeolites, 33–37 kJ/mole on the Pd catalysts, and 25–33 kJ/mole on magnesium and lanthanum oxides. It is suggested that the cyclohexyl complex, formed as an intermediate during hydrogenation of cyclohexene on Na-forms of the zeolites, is neither a carbocation nor a radical.

Hydrogenation of acetone on cationic forms of zeolites

1. Zeolites that contain the cations of the nontransition elements exhibit catalytic activity in the hydrogenation of acetone. 2. The activity and selectivity of zeolite catalysts depend on the nature of the cations, and the composition and structure of the zeolites.

The investigation of redox properties of palladium-zeolite catalysts

Palladium catalysts based on A, X, Y, chabazite, erionite, mordenite, TsVM, and TsVK zeolites are studied by the methods of temperature-programmed reduction and hydrogen desorption. Palladium is shown to be located in zeolite pores in all catalysts except Pd/mordenite for which 24 % of the palladium is located on the external surface of the zeolite. The dispersity of the palladium on the zeolites is determined by the amount of H2 evolved in the decomposition of the β-phase of PdH and by the value of the O/Pd ratio obtained by palladium oxidation in the 100 to 500 °C temperature range. According to the O/Pd ratio, the catalysts are divided into two groups: samples based on X, Y, chabazite, erionite, and mordenite (O/Pd=0.4 to 0.7), and catalysts containing A, TsVM, and TsVK zeolites (O/Pd=0.2 to 0.3). The catalysts of the first group are weakly active in the oxidative acetoxylation of propylene, while all of the catalysts of the second group except Pd/NaA are very active. The conclusion is drawn that the oxidation of palladium is not the limiting stage in the oxidative acetoxylation of propylene.

Metal-containing zeolite catalysts for the oxidative acetoxylation of propylene

Conclusions1.The possibility of obtaining metal-containing catalysts for the oxidative acetoxylation of propylene from synthetic high-silica zeolites was investigated. Activity is only exhibited by reduced bimetallic palladium-copper catalysts prepared by ion exchange.2.In order to obtain the given catalytic characteristics it is necessary to add the acid function of the zeolite at the concluding stage of the preparation of the catalyst.3.Best results with respect to the activity and selectivity are obtained on catalysts based on K, Na-erionite.

Oxidative interactions of propene with acetic acid on a Pd-zeolite catalyst

The interactions between C3H6, AcOH and O2 were investigated on 1.5 % Pd/TsVM catalysts prepared with and without addition of 15 % AcOK. Three states for surface oxygen on the promoted catalyst were distinguished. Two of them are involved in the oxidation of AcOH and C3H6 to CO2 and H2O, whereas the adsorbed species of the third type participates in the formation of allyl acetate. The O/Pd ratios for the promoted catalyst fall in the range from 3 to 4, the nonpromoted system is characterized by an O/Pd value of 0.5. IR-spectral data are used to discuss the reaction scheme for the formation of allyl acetate.

Effect of palladium and copper content of zeolite catalysts on the kinetic parameters of the oxidative acetylation of propylene

Conclusions1.Using the methods of mathematical planning of an experiment, a kinetic model has been obtained for the oxidative acetylation of propylene to allyl acetate and the effect of the composition of the Pd, Cu/mordenite catalyst on its parameters has been determined.2.The kinetic parameters (1g k0)0, Q, 1ga0 and E0 correlate strongly and form a gully on the surface of the minimized functional. Regularization of the values of the kinetic parameters was carried out by isolating a subregion of the gully satisfying the Boudart thermodynamic relationships.3.On varying the Pd and Cu content of the catalyst within the limits 0.1 to 3.0%, the activation energy and the logarithm of the preexponential factor of the rate constant vary over the range 2–11 kcal/mole and 0.255–3.453, respectively.

Determination of the reaction region for isomerization of xylenes on H-form Y zeolite

Conclusions1.Intracrystal diffusion of the reagent molecules does not constitute a limiting factor in the isomerization of xylenes on HY zeolite in an impulse microreactor at 350–500°C.2.The different variants of the dependence of the general and observed specific activities of a zeolite catalyst on the number of active centers have been considered and it has been shown that on the basis of the criteria suggested one can in most cases reliably judge whether the reaction is proceeding in the kinetic or the diffusion region.