Experimental Rate Constants Research Articles

Quantification of the gas phase methyl iodide using O2+ as the reagent ion in the PTR-ToF-MS technique

The charge-transfer-reaction between molecular oxygen ions (O2+) and methyl iodide (CH3I) is studied to investigate if consistent environmental quantification of the gas phase CH3I is possible without prior calibration. The neutral CH3I molecule was chosen because this compound is of atmospheric chemistry and environmental importance in the field of nuclear power plant safety and nuclear energy. Molecular oxygen was used as a reagent ion source in a commercial Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) to produce molecular oxygen ions (O2+). The use of O2+ ions allows for fast, sensitive and specific detection of gas phase CH3I via an electron exchange reaction O2+ + CH3I → CH3I+ + O2. The instrument response was linear in the 0.23–150 ppbv range and its sensitivity was humidity independent. The detection sensitivity of CH3I normalized by the O2+ count rate of 106 cps was found to be S = 22.6 ± 0.3 ncps/ppbv, independent of relative humidity. A typical O2+ primary ion signal was (2.0±0.2)×106 cps. The lowest measured CH3I concentration was 0.23 ± 0.10 ppb. Error is ±σ. The theoretical collision rate based on the dipole moment and molecular polarizability values is calculated using the Langevin collision rate (kL) approximation, the average-dipole-orientation (ADO) theory and the capture rate coefficient (kCAP) based on trajectory calculations. The experimental rate constant, kexp, for the electron transfer reaction between O2+ ions and CH3I is calculated to be 1.72±0.22×10-9 cm3s−1. Listed errors are ±σ and represent precision only. The experimentally determined value agrees very well with the theoretical collision rate values, kL=1.24×10-9 cm3s-1, kADO=1.73×10-9 cm3s−1 and kCAP=1.48×10-9 cm3s-1. The obtained results indicate that the PTR-MS technique is an excellent analytical method to quantify gas phase CH3I.

The impact of desorption kinetics from albumin on hepatic extraction efficiency and hepatic clearance: a model study.

Until now, the question whether slow desorption of compounds from transport proteins like the plasma protein albumin can affect hepatic uptake and thereby hepatic metabolism of these compounds has not yet been answered conclusively. This work now combines recently published experimental desorption rate constants with a liver model to address this question. For doing so, the used liver model differentiates the bound compound in blood, the unbound compound in blood and the compound within the hepatocytes as three well-stirred compartments. Our calculations show that slow desorption kinetics from albumin can indeed limit hepatic metabolism of a compound by decreasing hepatic extraction efficiency and hepatic clearance. The extent of this decrease, however, depends not only on the value of the desorption rate constant but also on how much of the compound is bound to albumin in blood and how fast intrinsic metabolism of the compound in the hepatocytes is. For strongly sorbing and sufficiently fast metabolized compounds, our calculations revealed a twentyfold lower hepatic extraction efficiency and hepatic clearance for the slowest known desorption rate constant compared to the case when instantaneous equilibrium between bound and unbound compound is assumed. The same desorption rate constant, however, has nearly no effect on hepatic extraction efficiency and hepatic clearance of weakly sorbing and slowly metabolized compounds. This work examines the relevance of desorption kinetics in various example scenarios and provides the general approach needed to quantify the effect of flow limitation, membrane permeability and desorption kinetics on hepatic metabolism at the same time.

Direct Dynamics Simulation of the Thermal 3CH2 + 3O2 Reaction. Rate Constant and Product Branching Ratios.

The reaction of 3CH2 with 3O2 is of fundamental importance in combustion, and the reaction is complex as a result of multiple extremely exothermic product channels. In the present study, direct dynamics simulations were performed to study the reaction on both the singlet and triplet potential energy surfaces (PESs). The simulations were performed at the UM06/6-311++G(d,p) level of theory. Trajectories were calculated at a temperature of 300 K, and all reactive trajectories proceeded through the carbonyl oxide Criegee intermediate, CH2OO, on both the singlet and triplet PESs. The triplet surface leads to only one product channel, H2CO + O(3P), while the singlet surface leads to eight product channels with their relative importance as CO + H2O > CO + OH + H ∼ H2CO + O(1D) > HCO + OH ∼ CO2 + H2 ∼ CO + H2 + O(1D) > CO2 + H + H > HCO + O(1D) + H. The reaction on the singlet PES is barrierless, consistent with experiment, and the total rate constant on the singlet surface is (0.93 ± 0.22) × 10-12 cm3 molecule-1 s-1 in comparison to the recommended experimental rate constant of 3.3 × 10-12 cm3 molecule-1 s-1. The simulation product yields for the singlet PES are compared with experiment, and the most significant differences are for H, CO2, and H2O. The reaction on the triplet surface is also barrierless, inconsistent with experiment. A discussion is given of the need for future calculations to address (1) the barrier on the triplet PES for 3CH2 + 3O2 → 3CH2OO, (2) the temperature dependence of the 3CH2 + 3O2 reaction rate constant and product branching ratios, and (3) the possible non-RRKM dynamics of the 1CH2OO Criegee intermediate.

Effect of dissolved organic matter on pre-equilibrium passive sampling: A predictive QSAR modeling study

Pre-equilibrium passive sampling is a simple and promising technique for studying sampling kinetics, which is crucial to determine the distribution, transfer and fate of hydrophobic organic compounds (HOCs) in environmental water and organisms. Environmental water samples contain complex matrices that complicate the traditional calibration process for obtaining the accurate rate constants. This study proposed a QSAR model to predict the sampling rate constants of HOCs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and pesticides) in aqueous systems containing complex matrices. A homemade flow-through system was established to simulate an actual aqueous environment containing dissolved organic matter (DOM) i.e. humic acid (HA) and (2-Hydroxypropyl)-β-cyclodextrin (β-HPCD)), and to obtain the experimental rate constants. Then, a quantitative structure-activity relationship (QSAR) model using Genetic Algorithm-Multiple Linear Regression (GA-MLR) was found to correlate the experimental rate constants to the system state including physicochemical parameters of the HOCs and DOM which were calculated and selected as descriptors by Density Functional Theory (DFT) and Chem 3D. The experimental results showed that the rate constants significantly increased as the concentration of DOM increased, and the enhancement factors of 70-fold and 34-fold were observed for the HOCs in HA and β-HPCD, respectively. The established QSAR model was validated as credible (RAdj.2=0.862) and predictable (Q2=0.835) in estimating the rate constants of HOCs for complex aqueous sampling, and a probable mechanism was developed by comparison to the reported theoretical study. Main finding of the workThe present study established a QSAR model of passive sampling rate constants and calibrated the effect of DOM on the sampling kinetics.

Molecular Dynamics Simulations of Cross‐Linked Phenolic Resins Using a United‐Atom Model

AbstractA new molecular modeling algorithm for conducting large‐scale molecular dynamics simulation studies of cross‐linked phenolic resins is developed using a united‐atom model. A phenol–formaldehyde polycondensation system is simulated by a pseudoreaction algorithm taking into consideration (i) the difference in the experimental reaction rate constants at ortho and para positions of phenolic units and (ii) the geometry of the reactants. To avoid formation of locally strained cross‐linked structures that can be generated in a typical cutoff‐distance‐based reaction scheme, a geometrical judgment constraint is applied in the reaction procedure. With this algorithm, cross‐linked network structures of phenolic resins with a maximum conversion (α) of 0.90 are obtained from 10 000 phenols. The density and the tensile modulus of the structure with α of 0.90 at 300 K are 1.2 g cm−3 and 5.4 GPa, respectively. This is in good agreement with experimental values. The strain‐free, highly cross‐linked network structures of phenolic resins exhibit a higher density and tensile modulus compared with structures generated in the absence of the geometrical cutoff. This result demonstrates that the geometrical judgment constraint can effectively avoid the formation of distorted and strained local structures and is necessary for accurate modeling of highly cross‐linked phenolic resins.

Can Manganese(III)‐Iodosylarene Act as an Oxidant Alongside High‐Valent Manganese(V)‐Oxo Complexes?

AbstractMetalloenzymes often utilize a high‐valent metal‐oxo species in their catalytic cycle that is formed through a combination of reduction/proton transfer steps from O2. In biomimetic chemistry, by contrast, the use of molecular oxygen is challenging and instead addition of iodosylarenes as terminal oxidants generates these high‐valent metal‐oxo intermediates. There has been controversy in the literature for many years, whether the iodosylarene (or one of its side‐products in a reaction with a metal center) can act as an active oxidant. Herein, we present a comprehensive theoretical study on the thioanisole oxidation by a range of possible oxidants originating from a reaction mixture of a Mn(III) complex with iodosylbenzene. We show here that actually there are multiple isomeric iodosylarene complexes in solution and a number of those react with substrates with rate‐determining barriers at par with high‐valent metal‐oxo species. In particular, the [MnIII(PhIO)], [MnV(O)(PhIO)] and [MnIV(O)‐I(Ph)‐O•] complexes are identified as competitive oxidants and as such care should be taken with interpreting experimental rate constants.

An experimental technique for determination of intrinsic burning rate constants of liquid fuels

The burning rate constant of the droplets of a liquid fuel solely characterized by the thermo-physical properties of the fuel and the oxidizer is an intrinsic characteristic of the fuel. The classical quasi-steady approach enables estimation of such a parameter in a highly idealized scenario with a range of simplifying assumptions. Furthermore, this quasi-steady method requires the knowledge of the thermo-physical properties of the fuel along with the expected adiabatic flame temperature. The current study utilizes droplet combustion experiments in natural gravity for the estimation of the intrinsic burning rate constants of pure fuels. A semi-empirical technique has been utilized to establish a correlation between the experimental and classical quasi-steady burning rate constants. The dimensions of the droplet flame were an important aspect of the model. The experiments have been conducted in a quiescent atmosphere of ambient air with droplets of n-heptane, n-decane, and nitromethane. Quartz fibers with a range of diameters were utilized to support the droplets and obtain a variation of the initial droplet diameters. The observed variation of the burning rate constant was recognized to be the result of the augmentative effects of natural convection and the conductive heat transfer through the supporting fiber.

Molecular mechanism of lytic polysaccharide monooxygenases.

The lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes that can enhance polysaccharide depolymerization through an oxidative mechanism and hence boost generation of biofuel from e.g. cellulose. By employing density functional theory in a combination of quantum mechanics and molecular mechanics (QM/MM), we report a complete description of the molecular mechanism of LPMOs. The QM/MM scheme allows us to describe all reaction steps with a detailed protein environment and we show that this is necessary. Several active species capable of abstracting a hydrogen from the substrate have been proposed previously and starting from recent crystallographic work on a substrate-LPMO complex, we investigate previously suggested paths as well as new ones. We describe the generation of the reactive intermediates, the abstraction of a hydrogen atom from the polysaccharide substrate, as well as the final recombination step in which OH is transferred back to the substrate. We show that a superoxo [CuO2]+ complex can be protonated by a nearby histidine residue (suggested by recent mutagenesis studies and crystallographic work) and, provided an electron source is available, leads to formation of an oxyl-complex after cleavage of the O-O bond and dissociation of water. The oxyl complex either reacts with the substrate or is further protonated to a hydroxyl complex. Both the oxyl and hydroxyl complexes are also readily generated from a reaction with H2O2, which was recently suggested to be the true co-substrate, rather than O2. The C-H abstraction by the oxyl and hydroxy complexes is overall favorable with activation barriers of 69 and 94 kJ mol-1, compared to the much higher barrier (156 kJ mol-1) obtained for the copper-superoxo species. We obtain good structural agreement for intermediates for which structural data are available and the estimated reaction energies agree with experimental rate constants. Thus, our suggested mechanism is the most complete to date and concur with available experimental evidence.

Size-dependent rate acceleration in the silylation of secondary alcohols: the bigger the faster.

Relative rates for the reaction of secondary alcohols carrying large aromatic moieties with silyl chlorides carrying equally large substituents have been determined in organic solvents. Introducing thoroughly matching pairs of big dispersion energy donor (DED) groups enhanced rate constants up to four times, notably depending on the hydrogen bond donor ability of the solvent. A linear correlation between computed dispersion energy contributions to the stability of the silyl ether products and experimental relative rate constants was found. These results indicate a cooperation between solvophobic effects and DED-groups in the kinetic control of silylation reactions.

Influence of thermodynamically unfavorable secondary structures on DNA hybridization kinetics.

Nucleic acid secondary structure plays an important role in nucleic acid–nucleic acid recognition/hybridization processes, and is also a vital consideration in DNA nanotechnology. Although the influence of stable secondary structures on hybridization kinetics has been characterized, unstable secondary structures, which show positive ΔG° with self-folding, can also form, and their effects have not been systematically investigated. Such thermodynamically unfavorable secondary structures should not be ignored in DNA hybridization kinetics, especially under isothermal conditions. Here, we report that positive ΔG° secondary structures can change the hybridization rate by two-orders of magnitude, despite the fact that their hybridization obeyed second-order reaction kinetics. The temperature dependence of hybridization rates showed non-Arrhenius behavior; thus, their hybridization is considered to be nucleation limited. We derived a model describing how ΔG° positive secondary structures affect hybridization kinetics in stopped-flow experiments with 47 pairs of oligonucleotides. The calculated hybridization rates, which were based on the model, quantitatively agreed with the experimental rate constant.

High‐Temperature Rate Constants for H + Tetramethylsilane and H + Silane and Implications about Structure–Activity Relationships for Silanes

ABSTRACTThe shock‐tube technique has been used to investigate the reactions H + SiH4 → H2 + SiH3 (R1) and H + Si(CH3)4 → Si(CH3)3CH2 + H2 (R2) behind reflected shock waves. C2H5I was used as a thermal in situ source for H atoms. For reaction (R1), the experiments covered a temperature range of 1170–1251 K and for (R2) 1227–1320 K. In both cases, the pressures were near 1.5 bar. In these experiments, H atoms were monitored with atomic resonance absorption spectrometry. Fits to the H‐atom temporal concentration profiles applying postulated chemical kinetic reaction mechanisms were used for determining the rate constants k1 and k2. Experimental rate constants were well represented by the Arrhenius equations k1(T) = 2.75 × 10−9 exp(−37.78 kJ mol−1/RT) cm3 s−1 and k2(T) = 1.17 × 10−7 exp(−86.82 kJ mol−1/RT) cm3 s−1. Transition state theory (TST) calculations based on CBS‐QB3 and G4 levels of theory show good agreement with experimentally obtained rate constants; the experimental values for k1 and k2 are ∼40% lower and ∼50% larger than theoretical predictions, respectively. For the development of a mechanism describing the thermal decomposition of tetramethylsilane (Si(CH3)4; TMS), also TST‐based rate constants for reaction CH3 + Si(CH3)4 → Si(CH3)3CH2 + CH4 (R3) were calculated. A comparison between experimental and theoretical rate constants k2 and k3 with available rate constants from the literature indicates that Si(CH3)4 has very similar reactivity toward H abstractions like neopentane (C(CH3)4), which is the analog hydrocarbon to TMS. Based on these results, the possibility of drawing reactivity analogies between hydrocarbons and structurally similar silicon‐organic compounds for H‐atom abstractions is discussed.

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules.

The recombination of CF3 and CHF2 radicals in a room-temperature bath gas was used to prepare vibrationally excited CF3CHF2* molecules with 101 kcal mol-1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF3, CF3(F)C: and C2F4 product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF3(F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 104, 4.7 × 104, and 1.1 × 104 s-1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E0) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol-1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with 1,1-HF elimination being more important than 1,2-HF elimination. The trend of increasing threshold energies for both 1,1-HF and 1,2-HF processes with the number of F atoms in the fluoroethane molecule is summarized and investigated with electronic-structure calculations. Examination of the intrinsic reaction coordinate associated with the 1,1-HF elimination reaction found an adduct between CF3(F)C: and HF in the exit channel with a dissociation energy of ∼5 kcal mol-1. Hydrogen-bonded complexes between HF and the H atom migration transition state of CH3(F)C: and the F atom migration transition state of CF3(F)C: also were found by the calculations. The role that these carbene-HF complexes could play in 1,1-HF elimination reactions is discussed.

OH-initiated mechanistic pathways and kinetics of camphene and fate of product radical: a DFT approach.

Present manuscript represents the DFT studies on the oxidation reaction of camphene initiated by OH radical and fate of product radicals using M06-2X functional along with 6-31+G(d,p) basis set. Intrinsic reaction calculation is done for transition states involving OH-addition reactions which proceed via reaction complexes proceeding to the formation of transition states. The rate constant calculated by using canonical transition state theory at 298K and 1atm is found to be 5.67×10-11cm3molecule-1s-1 which is in good agreement with the experimental rate constant. The atmospheric lifetime of the titled molecule has also been reported in our work.

Theoretical Investigations on the Mechanism and Kinetics of OH Radical Initiated Reactions of Monochloroacetic Acid.

The oxidation mechanism of monochloroacetic acid (CH2ClCOOH) by OH radical has been systematically investigated employing quantum mechanical methods coupled with kinetic calculation using canonical variational transition state theory. Three distinct transition states were identified for the titled reaction, two corresponding to the hydrogen atom abstraction and one corresponding to the chlorine atom abstraction. The rate constants of the titled reactions are computed over the temperature range 278-350 K, and the branching ratios calculated for the hydrogen atom abstraction from the -C(O)OH site and the -CH2Cl site are 25 and 75%, respectively, at 298 K. The computed branching ratio indicates that the kinetically favorable reaction is the hydrogen atom abstraction from the -CH2Cl site resulting in the formation of CHClC(O)OH radical, which further undergoes secondary reaction with O2 and other atmospheric species. The calculated overall rate constant for the hydrogen atom abstraction reactions is in consistent with the reported experimental rate constant. The atmospheric lifetime of CH2ClCOOH is found to be around 18 days.

Application of Kalman filter to determination of coal liquefaction mechanisms using discrete time models

Seven different liquefaction mechanisms that consist of reversible and irreversible steps are suggested for a Turkish lignite (Tunçbilek) in tetralin with the use of microwave heating. Compliance of the proposed mechanisms are determined by forming first order linear Discrete-time models with the experimental data and reaction rate constants are determined with the program written in MATLAB with the use of the Kalman filter. The most appropriate suggested model is determined by looking at the sum of the experimental data and squared differences of the values calculated with the model. The magnitude of the reaction rate constants is examined for the models that best fit. The obtained results show that majority of the oil is formed directly from coal. Furthermore, whereas coal:oil reaction step has maximum reaction rate constant, coal:asphaltene and coal:preasphaltene reaction steps have minimum rate constant. Models containing parallel and reversible steps are seen to provide a better fit to the experimental data. The best fit was obtained with model that has both reversible (between asphaltene:coal, asphaltene:oil, and asphaltene:preasphaltene) and irreversible (coal:oil, coal:preasphaltene and preasphaltene:oil) reaction steps. The model also evidenced that the reversible reactions are critical on the liquefaction of Tunçbilek coal.

Reactions of N1-Methyl-4-nitro-2,1,3-benzoselenadiazolium Tetrafluoroborate with Aliphatic and Cyclic Amines in Acetonitrile: Kinetic and Structure-Reactivity Correlations

The nucleophilic addition reactions of N1-methyl-4-nitro-2,1,3-benzoselenadiazolium tetrafluoroborate 1 with aliphatic amines 2a–c (diethylamine 2a, dipropylamine 2b, and allylamine 2c) have been kinetically studied by UV–vis spectroscopy in acetonitrile solution at 20°C. The kinetic data have been analyzed, using the Mayr equation, allowing the quantification of the electrophilicity parameter (E) value of benzoselenadiazolium cation 1 (E = −14.72). The reliability of parameter E has been reasonably verified by comparison of calculated and experimental second-order rate constants for the reactions of cation 1 with other amines 2d–f (pyrrolidine 2d, piperidine 2e, and morpholine 2f) under the same conditions as those of the amines 2a–c. A linear Bronsted plot (R2 = 0.9945) with a βnuc value of 0.55 has been obtained for the reactions of 1 with the secondary amines employed in the present work. Interestingly, satisfactory correlation between the log values of measured and calculated rate constants with a slope very close to unity has been obtained and discussed.

DFT study on abstraction reaction mechanism of oh radical with 2-methoxyphenol

Reaction mechanism of 2-methoxyphenol (2MP) (guaiacol) with OH radical has been performed using density functional theory methods BH&HLYP and MPW1K method with 6-311++G(d,p) basis set. Single-point energy calculations were done using CCSD(T)/6-311++G(d,p). The theoretical results reveal that the hydrogen abstraction from methoxy group is found to be the dominant reaction channel with an energy barrier of 9.31 kcal/mol. Also, time-dependent density functional theory calculations have been performed using BH&HLYP/6-311++G(d,p) level of theory, and the results reveal that the reactions occur in ground state than the excited state. The results of reaction force profile indicate that structural rearrangements are most influential with high percentage than the relaxation process. The calculated theoretical rate constants (12.19 × 10−11 cm3 molecule−1 s−1) are in good agreement with the experimental rate constant. The atmospheric lifetime of 2-methoxyphenol with respect to OH radicals is 2.27 hours, which implies that OH radical plays an important role in the degradation of 2MP. The Wiberg bond index of the abstraction reaction reveals that the bond order is concerted, partially synchronic. The reactant-like transition state satisfies Hammond postulate, which eventually results in an exothermic reaction, and the product-like transition state reveals in endothermic nature.

Concentration Dependence of the Rate of Catalytic Isotopic Exchange of Hydrogen with Water Vapor on the Catalyst RKhTU-3SM

One method of separating hydrogen isotopes is chemical isotopic exchange of hydrogen with liquid water, combined with electrolysis of water. At present, different mathematical models are used to calculate the characteristics of newly developed setups. They all have the problem of inadequate data on the characteristics of the chemical isotopic exchange process occurring at medium and high deuterium concentrations. The present work is devoted to investigating one stage of chemical isotopic exchange – catalytic isotopic exchange between hydrogen and water vapor at high deuterium concentrations in application to the catalyst RKhTU-3SM. It is shown that the experimental rate constant of isotopic exchange for the pair protium – deuterium increases by almost a factor of two, while for exchange with tritium increasing the deuterium concentration from 5 to 95% does not change the experimentally observed rate constant to within the measurement error.

Low-Temperature Experimental and Theoretical Rate Constants for the O(1D) + H2 Reaction

In the present joint experimental and theoretical study, we report thermal rate constants for the O(1D) + H2 reaction within the 50-300 K temperature range. Experimental kinetics measurements were performed using a continuous supersonic flow reactor coupled with pulsed laser photolysis for O(1D) production and pulsed laser-induced fluorescence in the vacuum ultraviolet wavelength range (VUV LIF) for O(1D) detection. Theoretical rate constants were obtained using the ring polymer molecular dynamics (RPMD) approach over the two lowest potential energy surfaces 11A' and 11A″, which possess barrierless and thermally activated energy profiles, respectively. Both the experimental and theoretical rate constants exhibit a weak temperature dependence. The theoretical results show the dominant role of the 11A' ground state and that contribution of the 11A″ excited state to the total thermal rate decreases dramatically at lower temperature. Agreement between the experimental and theoretical results is good, and the discrepancy does not exceed 25%. It is argued that these differences are likely to be due to nonadiabatic couplings between the 11A' and 21A' surfaces.

Experimental Investigation of Concentration Dependency of Hydrophobic Catalyst Performance in Reaction of Isotope Exchange Between Water Vapor and Hydrogen

Vapor phase catalytic exchange is an important part of many hydrogen isotope separation processes. Some industrial hydrogen isotope separation processes are performed in a wide deuterium concentration range. The performance of catalysts in hydrogen-water vapor exchange reaction in the upper deuterium concentration limit is poorly investigated. The paper presents results of an investigation of catalytic activity of three catalyst types at the upper and lower limits of the deuterium concentration range. All catalyst experimental rate constants in protium-deuterium exchange demonstrated a tendency to increase with the growth of deuterium concentration. Experimental rate constants of catalysts in protium-tritium and deuterium-tritium exchange were found to remain constant. In this work the authors propose a method to be used for catalyst performance evaluation to obtain catalyst performance data for liquid phase catalytic exchange process models.