Studies of the dynamic properties of heterogeneous catalytic reactions in a closed adiabatic gradientless system over biographically inhomogeneous catalyst surface

The dynamic of a closed adiabatic system of constant volume consisting of an ideal gas mixture and particles adsorbed over the biographically inhomogeneous catalyst surface, has been studied. The asymptotic stability of a point of detailed equilibrium in each reaction simplex has been proved.

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New correlations for the analysis of isothermal critical phenomena in heterogeneous catalytic reactions

Abstracr The kinetic hysteresis was analyzed for the simplest particular mechanism of a catalytic reaction exhibiting isothermal critical phenomena (the Langmuir-Hinshelwood mechanism). New correlations between the kinetic characteristics at the critical points of kinetic hysteresis were obtained.Hyprotech, 400, 119 14th Street, N.-W., Calgary, Alberta, T2N 1Z6, Canada.Kiev Polytechnical Institute of Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 153–156, May–June, 1996. Original article submitted September 13, 1995.     

Selectivity of complex heterogeneous catalytic reactions over energetically nonuniform surfaces

The selectivity in parallel and consecutive heterogeneous catalytic reactions over nonuniform surfaces has been analyzed within the framework of the surface electron gas model. Equations for the selectivity are derived in the case of slow adsorption (no rate-limiting steps). Conditions when the nonuniform character of real catalytic surfaces should be taken into account in modeling of the selectivity behavior are discussed.     

Steady states of three-step heterogeneous reactions on a decaying catalyst

A slow decay of the catalyst's activity may lead to qualitative changes in the phase pattern of the reaction, depending on the reversibility of steps involved in the reaction mechanism.

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Ligand-free catalytic system for the synthesis of diarylethers over Cu2O/Cu-CNTs as heterogeneous reusable catalyst

Various substituted diarylether derivatives were prepared by using heterogeneous reusable Cu₂O- and Cu-coated carbon nanotubes (Cu₂O/Cu-CNTs) as catalyst under ligand-free conditions, which provided good to excellent yields. The catalyst was characterized by TEM, XRD, and AAS analysis. The effects of solvent, base, and amount of catalyst for the O-arylation were investigated. The catalyst could be recovered by simple filtration from the reaction mixture without further treatment and reused several times with consistent catalytic activity. In addition, CNTs could also be recovered from the used Cu₂O/Cu-CNTs by a simple acid treatment.     

On the surface steps of a heterogeneous catalytic reaction

Based on a study of the properties of intermediate complexes in the reactions of low-temperature ammonia oxidation and nitrogen oxide reduction in the presence and absence of oxygen on various catalysts, it was hypothesized that the sequence of steps in the formation of reaction products on chemically different catalysts can be the same if the initial adsorption forms of reactants are identical. In this case, variations in catalysts or reaction conditions affect the ratio between reaction rates.     

Conjugation of linoleic acid over a hydrogen pre-activated heterogeneous catalyst

Development of a new heterogeneous catalytic pathway for isomerization of linoleic acid to conjugated linoleic acids at mild reaction conditions over Ni/H-MCM-41 in a soluted system.     

Intensification of heterogeneous catalytic gas-fluid interactions in reactors with a multichannel monolithic catalyst

The review discusses the present-day state of research, industrial experience, and prospects for application of reactors with a multichannel catalyst for gas-fluid catalytic reactions.     

蘑菇多酚氧化酶的性质及其催化反应动力学的研究

本文用二次丙酮法从磨菇中提取多酚氧化酶，用分光光度法测定多酚氧化酶催化邻苯二酚的氧化反应。实验结果表明：酶作用的最佳条件是pH等于7、温度30℃，反应活化能等于21．20kJ．mol-1。     

Kinetics of simultaneously occurring heterogeneous catalytic reactions with a common reagent (competing reactions)

The mutual effect of heterogeneous kinetic reactions with a common reagent is examined on the assumption that the mechanisms of the reactions do not change when they occur simultaneously. It was shown that with certain mechanisms typical of heterogeneous catalysis the simultaneous occurrence of the reactions can lead not only to retardation but also to acceleration of one reaction by the other.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 497–501, July–August, 1990.     

Specific features of the catalytic behavior of supported palladium nanoparticles in heterogeneous catalytic reactions

Specific features of the catalytic behavior of supported palladium nanoparticles were analyzed in terms of both the size of the particles and their interaction with the support. The influence of these factors on the activity and selectivity of palladium nanoparticles in carbon-carbon bond hydrogenolysis, hydrogenation of aromatic compounds, olefins, and acetylenes, hydrodechlorination, as well as complete oxidation of organic compounds was discussed. It was shown that the optimal nanoparticle size depends on the type of the reaction and also such factors as the nature of interaction between the nanoparticles and support, absorptivity of the substrates and catalytic reaction products, and electronic and crystal structure of the nanoparticles.     

Hydroxylated surface of GaAs as a scaffold for a heterogeneous Pd catalyst

A novel use of GaAs, namely, as a scaffold for a heterogeneous palladium catalyst, is proposed. Hydroxy groups on the GaAs surface play important roles. During the adsorption of Pd(OAc)(2) on the GaAs surface, the hydroxy groups attract Pd(ii) species by anion exchange. A subsequent redox reaction proceeds to generate Pd(0) nanoparticles, which are stabilized on the GaAs surface. This process is confirmed by surface-sensitive measurements: diffuse reflection IR spectroscopy and X-ray photoelectron spectroscopy. Moreover, a more bulk-sensitive measurement, hard X-ray photoemission spectroscopy with synchrotron radiation, also supported our considerations. The amounts of Pd(0) nanoparticles on the surface were evaluated by catalytic activity, yield, and recyclability in the Heck reaction, in addition to the deposit test.     

Changes in the catalytic properties of a multicomponent molybdenum catalyst under vibro-fluidized catalyst bed conditions

Activation effect of oxidative dehydrogenation of butene-l on a multicomponent molybdenum catalyst at various temperatures has been studied by pulse and flow techniques. It is shown that under vibrofluidization not only reactive but also adsorption properties of the catalyst surface change. Oxygen consumption in the reaction process has been examined.

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Preparation of a novel CuI/PCMS heterogeneous catalyst for Heck-type cross-coupling reactions

A novel and environmentally friendly heterogeneous catalyst has been prepared through the wet impregnation of copper(I) species onto the highly porous chitosan microspheres (CuI/PCMS). This novel CuI/PCMS heterogeneous catalyst with no additional ligands is much better than CuI homogeneous catalysts when applied in Heck reactions. Moreover, the reaction conditions are much milder than those for the similar copper catalysts mediated cross-coupling reactions reported in the literature. PCMS has been demonstrated not only the excellent solid support, but also have many unique functional groups to chelate the copper (I) species to enhance its catalytic activity.     

Selectivity in consecutive heterogeneous catalytic reactions: Case of polyatomic molecules

Consecutive catalytic reaction mechanism of type A^(+B)C^(+B)D is considered and the polyatomic nature of adsorbed molecules is taken into account. The equations for the selectivity are presented and compared with ones for consecutive reactions with monoatomic reagents.     

Dynamic properties of a heterogeneous catalytic reaction with several steady states

For the simplest catalytic mechanism (three-stage) permitting several steady states of the surface, a qualitative analysis of the properties of its kinetic model trajectories has been performed. Types of the steady states have been determined. Absence of oscillations (damped and undamped) has been shown.

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Для простейшего каталитического механизма (трехстадийного), допускающего несколько стационарных состояний поверхности, проведен качественный анализ свойств траекторий его кинетической модели. Определены типы стационарных состояний. Показано отсутствие осцилляций (затухающих и незатухающих).