Kinetic equation for reversible heterogeneous catalytic reactions

It is demonstrated that when operating far from equilibrium, despite the non-linearity of a complex reaction system, the overall rate of a heterogeneous catalytic reaction is expressed by a classical equation, where the equilibrium constant is determined by the ratio of constants of the forward and reverse reaction, which do not include the lateral interactions in the adsorbed layer.     

Kinetic isotope effect in hydrogen isotope exchange between water and phosphines

The kinetic parameters of the tritium exchange between^*H₂O(^*D₂O) and (CH₃)₂PH in the gas phase and between^*H₂O(^*D₂O) and (C₆H₅)₂PH in liquid were measured. Both reactions appeared to be heterogeneous ones. The^*HH/^*DD kinetic isotope effects were estimated and compared with the results of exchange between methanol and phosphines. The differences in isotope effects are explained by the change of the symmetry of the four center cyclic transition complex resulting from the various type of solvation of this complex.     

Kinetic models of heterogeneous catalytic reactions (review)

A complex approach for obtaining comprehensively substantiated kinetic models in heterogeneous catalysis is proposed. The kinetic models of catalytic conversions of different classes of organic compounds, estabished for the first time by this method, are described. Some theoretical premises and the consequences of this study are examined.Review of data from research awarded the Academy of Sciences of the USSR D. I. Mendeleev Prize in chemical sciences for 1990.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2699–2717, December, 1991.     

Kinetic isotope effect in pentavalent plutonium disproportionation in heterogeneous systems

A kientic isotope effect in Pu(V) disproportionation in nitric acid solutions have been observed in a heterogeneous system with phenyloctylphosphonic acid deposited on hydrophobized silicagel. The isotope separation coefficient for²⁴²Pu/²³⁹Pu isotopes was found to be 1.022 at 25°C. The rate constant of Pu(V) disproportionation in this heterogeneous system was determined to be 5.0±0.6 1²mol^–2s^–1 at 25°C, [HNO₃]= 0.87–1.5 mol l^–1 and 11 phase ratio (10% extractant on the support).     

Kinetic coupling and selectivity pattern in consecutive heterogeneous catalytic reactions

The kinetic coupling in the case of complex coupled catalytic reactions leads to substantial changes in selectivity. The consecutive catalytic reaction mechanism of type A^(+B)C^(+B)D is considered and it is demonstrated that the selectivity pattern is determined by the pressure of B.     

Kinetics of heterogeneous isotope exchange in the systems containing porous particles

The porous particle is represented as a system of slabs of different thickness in order to evaluate the kinetic curve of isotope exchange. The physical reasons of such a representation are discussed. The model curves are compared for different distributions of slab thickness.     

Kinetic isotope effect and mechanism of catalytic reaction of hydroxybenzenes with epichlorohydrin

Kinetic data are presented for catalytic reactions of 3-nitrophenol and 4,4′-dihydroxydiphenyl sulfone with epichlorohydrin. Magnitudes of the kinetic isotope effects have been determined for these reactions, and a mechanism of catalysis is proposed. Donetsk State University, 24 Universitetskaya ul., Donetsk 340055, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 302–305, September–October, 1998.     

A generalized equation describing isotope exchange kinetics at solid-liquid interface

A generalization of the kinetic equation for the isotope exchange at solid—liquid interface is presented. The generalized equation may be used to describe kinetics of the isotope exchange process limited by surface reactions and diffusion without assumption of spherical symmetry of solid particles.

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Eine generalisierte Gleichung für die Kinetik des Isotopenaustausches an Fest-Flüssig-Phasengrenzen

Zusammenfassung Es wird eine generalisierte kinetische Gleichung angegeben, die die Kinetik des Isotopenaustausches an Fest-Flüssig-Phasengrenzen beschreibt, wobei der Austauschprozeß durch Oberflächenreaktionen und Diffusion ohne der Annahme sphärischer Symmetrie für die festen Partikel begrenzt ist.

     

Effect of tritium on hydrogen isotope exchange reaction in a heterogeneous system

In order to reveal the effect of tritium (³H or T) on hydrogen isotope exchange, the exchange reaction between a certain compound (solid or liquid) and a tritiated one (gas or solid) was observed in gas-solid or liquid-solid systems. The reaction was analyzed using the data obtained and theA-McKay plot method, and it has been quantitatively clarified that the effect of T on the reactivity of a material is changed with (1) the degree of polymerization of the material, (2) the kind of functional groups in the material, and (3) the reaction system.     

Separation of radioiodine by multistage isotope exchange in a heterogeneous liquid system

The separation of radioiodine from water by multistage isotope exchange between iodide and molecular iodine in a heterogeneous liquid system under both static and dynamic conditions has been studied in two model arrangements. Equations were derived which enable the calculation of the theoretical separation efficiency in dependence on both the volume concentration and concentration of the carrier of radioiodide in water. It was found that under the same conditions, the calculated values are in a satisfactory agreement with experimentally determined values of the separation efficiency.     

use of fixion 50X8 cation exchange plates for heterogeneous isotope exchange in radiochemical analysis

A method for the simultaneous isolation of a number of elements (In, Y, Zn, Co, Cd) from their mixture has been developed. The method is based on heterogeneous isotope exchange between the radionuclide of the element to be determined in the solution and a cation exchange plate saturated with the inactive form of the same element. The investigations were carried out with “Fixion 50X8” plates (Hungary) measuring 1 cm². 5–6 ml of the test solution was used. In order to properly choose the optimum saturation conditions of the plates with the element to be determined the kinetics of sorption and isotope exchange and the pH were studied. It can be excepted that in the future this procedure will be widely used in the radioanlytical isolation and determination of many elements by isotope exchange and activation analysis. The automation of this radioanalytical procedure for serial analysis will become possible owing to the simplicity and elegance of the experimental technique.     

Determination of iodine in organic iodine compounds by non-equilibrium isotope exchange in a heterogeneous exchange system

Some water-soluble organic iodine compounds (aqueous solution) can be analyzed for iodine by isotopically exchanging with labelled elementary iodine (organic solution). The method is applicable to exchange systems in which the rate of the exchange is rather small but measurable, before the exchange equilibrium is attained. The iodine content of iodoaromatic amino acids such as 5-iodouracil and 3,5-diiodotyrosine can be determined within an error of ±4%.     

High temperature solid state catalytic isotope exchange with deuterium and tritium

A method for synthesizing tritium- or deuterium-labeled amino acids, peptides and biogenic amines through high temperature solid state catalytic isotope exchange (HSCIE) is proposed. The dependence of the degree of isotope exchange in HSCIE on the structure of the compound, the reactivity of hydrogen at different carbon atoms and the conditions of the process has been examined. If HSCIE is performed in the temperature range of 373 to 413K, the selectivity of isotopic label incorporation comes to 70% or higher. When the tritium label is introduced into peptides, they retain the configuration of asymmetric atoms, even upon the substitution of tritium for hydrogen at the -carbon atoms of the amino acid residues. HSCIE at 453–513K leads to an even distribution of the isotopic label over the organic compound molecule. The results of³H NMR spectroscopy highlighting the distribution of the tritium label in the organic compound molecules are presented. The configuration of asymmetric atoms in amino acids is preserved to a high extent upon 80–90% substitution of isotopes for hydrogen atoms.Presented at the 12th Radiochemical Conference, Marianské Lazné May 7–11, 1990.     

Some considerations on the treatment of the kinetic data of heterogeneous isotope exchange

A direct curve simulation treatment has been worked out for the evaluation of the kinetic curves of heterogeneous isotope exchange. Based on the data obtained by a personal computer some considerations have been made on the transport processes in the fully and half exchanged sodium forms of crystalline zirconium phosphate.     

Highly active iridium(I) complexes for catalytic hydrogen isotope exchange

Practically convenient methods have been developed for the preparation of new iridium complexes, possessing bulky N-heterocyclic carbene and phosphine ligands; these routinely handled complexes are highly active catalysts within directed hydrogen isotope exchange processes.     

Kinetic isotope effect during acid hydrogen exchange in σ-benzyl-π-cyclopentadienyliron dicarbonyl

Conclusions The kinetic isotope effect K_D/K_T was measured during acid hydrogen exchange in -C₅H₅-(CO)₂Fe--CH₂C₆H₅. The obtained K_D/K_T value testifies in support of the generality of the mechanisms of hydrogen exchange in the benzene ring of this complex and in other derivatives of the benzene series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 221–222, January, 1979.     

Kinetic acidity of aliphatic hydrocarbons. Hydrogen isotope exchange with cesium cyclohexylamide in cyclohexylamine

Kinetic acidities are reported for methane, ethane, propane, cyclopropane, isobutane, neopentane, tetramethylbutane, norbornane, nortricyclene, and adamantane by tritiodeprotonation or deuteriodeprotonation in cyclohexylamine catalyzed by cesium cyclohexylamide.     

Kinetic isotope effect in proton exchange processes between methanol and water in inert solvents

The kinetic isotope effect in proton exchange between methanol and water in CCl₄ solution was studied by¹H and²H NMR and kinetic IR spectroscopy. The exchange rate increases in the series CD₃OH+H₂O3OD+H₂O3OD+D₂O. It has been concluded that the limiting step of the reaction involves the formation of an H-bonded cyclic intermediate.

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¹H ²H - CCl₄. , CD₃OH+H₂O3OD+H₂O3OD+D₂O. , - -.

     

Study of solid-state catalytic isotope exchange of hydrogen inl-hydroxyproline under the action of spillover tritium

Reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) of hydrogen in L-hydroxyproline was studied byab initio quantum-chemical calculations. A one-center synchronous mechanism of isotope exchange between the amino acid and the H₃O⁺ model acidic center was considered. The structures of transition states of the reaction and the activation energies were determined. Relative reactivity of the C−H bonds in the hydroxyproline molecule under conditions of HSCIE was studied. The results obtained are in agreement with experimental data on the stereoselectivity and regioselectivity of the HSCIE reaction,viz., the lower the calculated activation energy of isotope exchange, the larger the portion of hydrogen substituted by tritium in a given position of the amino acid molecule. The enhancement of the reactivity under conditions of solid-state isotope exchange can be associated with additional interaction between the exchanging H atoms and the electron-donor O and N atoms of the amino acid molecule in transition state. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1056–1060, June, 1999.     

High-throughput heterogeneous catalytic science

High-throughput experimentation in heterogeneous catalysis has recently experienced nearly exponential growth. Initial qualitative screening has evolved into quantitative high-throughput experimentation, characterization, and analysis. This allows high-throughput catalysis now to rise above simple screening to the level of fundamental understanding of reaction mechanisms, which will lead on a faster path to the Holy Grail of catalysis: rational catalyst design.