Theoretical Analysis of the Motional Model of Nonlinear Heterogeneous Catalysis

In this paper, a model of the motional nonlinear heterogeneous catalysis process is discussed using the characteristic line method, the analytical results of elution profile are obtained and the formula which determines the parameters of reaction rate and adsorption isotherm through the motional measurement data under the nonlinear condition is given.     

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt_2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S~(2-) to St~- (stearate ion). Characterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i. e. CdS particle inserts in the CdSt_2 molecular layers to form a sandwich-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.     

Molecular, Thermodynamic, and Kinetic Parameters of the Free Radical C2H5 · in the Gas Phase

The wave function, energy, equilibrium geometry, and normal vibration frequencies of the ground state of the free radical C₂H₅ ^· were obtained by ab initio calculations with inclusion of electron correlation effects at the UB3LYP/6-311++G^{* *} level. The resulting molecular parameters were used to estimate the thermodynamic functions of an ideal gas of C₂H₅ ^·. From the thermodynamic functions of C₂H₅ ^·, I^·, C₂H₅I, C₂H₄, and HI and the kinetic curves of isothermal pyrolysis of ethyl iodide, the absolute rate constants of elementary reactions of free ethyl radical and the mentioned iodine compounds were estimated. The dissociation energy E _{D , 0}(C₂H₅-I) and the standard formation enthalpy _f H ⁰298 (C₂H₅ ^·) were found.     

Association-Assisted Kinetics of Pentanol-1 and Heptanol-1 Oxyethylation: Kinetic Parameters of Reactions and Association Parameters of Alcohols in the Series Butanol-1–Heptanol-1

The kinetics of pentanol-1 and heptanol-1 oxyethylation in the absence and in the presence of solvents (dodecane, p-xylene, and 1,4-dioxane) is studied under the conditions of base catalysis at 80–150°C and the concentrations of the catalyst (the corresponding sodium alkoxide) and ethylene oxide in the starting mixture of 1 and 10^–3–10^–1 mol/l, respectively. The experimental results are adequately described by the rate law that takes into account the association of alcohol molecules via hydrogen bonds. A hypothesis is advanced that an associate consisting of n alcohol molecules acts as a kinetically independent species in this reaction. The kinetic and association parameters for alcohols in the C₄–C₇ series are compared with the published data.     

Anomalies in the Change of Volumetric Parameters of the Diels–Alder Reaction in Solution

In this article negative values of the activation volume in retro-Diels–Alder reactions are interpreted in terms of the different possibilities of penetration of the solvent molecules into the sterically branched structures of the adduct and activated complex. Empty spaces, inaccessible to penetration of solvent molecules, lead to increases of the molar volume of the screened adducts in solution and, consequently, to a less negative value of the Diels–Alder reaction volume. The values of partial molar volumes of anthracene, maleic anhydride and the adducts cyclopentadiene–maleic anhydride, anthracene–maleic anhydride and anthracene–tetracyanoethylene, in several solvents, were calculated from the solution density data.     

Kinetic Analysis of an Enzyme-containing Polymer Modified Electrode

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Theoretical Study on the Mechanisms and Kinetic Parameters for the Initiation Reaction of Grubbs–Hoveyda Catalyst

Russian Journal of Physical Chemistry A - In this work, typical alkenes and Grubbs–Hoveyda catalyst (Cat1) were selected to study the mechanism and kinetic parameters (the entropies,...     

Determination of Kinetic Parameters and Metal Ions in Urea-Urease System Based on the Biochemical Reaction Heat Induced Laser Beam Deflection

Reaction heat induced laser beam deflection is a new analytical method which came in tobeing in 1993', by probing the gradient of the refraction index which was induced byreaction heat with a laser probe beam, one can relate the laser beam deflection to theconcentration of the sample.In this paper, the method was used for the study of the kinetic process for ureaurease system. It is well known that urease catalyzes the hydrolysis of urea as follows fUreaseNHZCONHZ HZO~ CO2 2NH3 QThe pro…     

Correlation Analysis of the Runoff of the Rivers and the Seisms in China

In recent hundred years the annual discharge variations of the Changjiang River (represented by the Yichang station) and the Huanghe River (represented by Shanxian and Tangnaihe, respectively) have closely related to the geographical distribution of the earthquakes coming about in China in the same year, Both the occurrence of the destructive seism or seismic swarm in the river basins and the disappearance of the shocks in the east and south of the basins are the conditions that the Changjiang and Huanghe Rivers are the high flow while that the strong earthquake of magnitude 7 or more occurred in North China is the condition for the Changjiang low flow year and that of 6 or more in the Qilian Mountains area is for the Huanghe River. In the latter part of this paper, a 2-year sample is given to explain that the conditions of the 2 rivers being high flow years are that the north-south seismic belt is active and in the meanwhile no seism occurred in South China, and those of the low flow year are that the     

Kinetic of Adsorption of Urea Nitrogen onto Chitosan Coated Dialdehyde Cellulose under Catalysis of Immobilized Urease

The adsorption of urea nitrogen onto chitosan coated dialdehyde cellulose (CDAC) under catalysis of immobilized urease in gelatin membrane (IE) was studied in batch system. The pseudo first-order and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model.     

Kinetic analysis of the crystallization processes in the glasses of the Bi–As–S system

Kinetic analysis of the crystallization process in Bi₄(As₂S₃)₉₆ and Bi₆(As₂S₃)₉₄ glasses was performed based on DSC curves recorded under non-isothermal measurement conditions. Samples were thermally treated at different heating rates in the temperature range 300?C770?K. The activation energy of crystallization E and the pre-exponential factor K ₀ are determined by the Kissinger method and the characteristic crystallization parameters m and n of investigated glasses by the Matusita method. For both crystallization processes the glass with 4 at.% of Bi is characterized by the mechanism of volume nucleation, which is manifested in the form of two-dimensional growth at the first crystallization process, and as three-dimensional at the second one. On the other hand, in the sample with 6 at.% Bi, the average value of the parameter m is close to one, which indicates one-dimensional crystal growth. Compatibility of the values of the parameters m and n suggests that this sample has a large number of crystallization centers, which do not increase significantly during the thermal treatment.     

Kinetic Regularities of the Kabachnik–Fields Reaction under Catalysis by Sulfonic Cation Exchangers Based on Petroleum Asphaltenes

Kinetics and Catalysis - Strongly acidic cation exchangers were obtained by the sulfonation and successive sulfonation and nitration of petroleum asphaltenes. The cation exchangers were...     

Micellar Catalysis on Pentavalent Vanadium Ion Oxidation of D-Sorbitol in Aqueous Acid Media: A Kinetic Study

Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the concentrations of D-sorbitol, vanadium(V), H⁺ and HSO₄⁻. These observations remain unaltered in the presence of externally added surfactants. The effects of the cationic surfactant (i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to different extents. SDS and TX-100 can be used as catalysts in the production of D-glucose from D-sorbitol.     

Detection of Synthetic Antioxidants: What Factors Affect the Efficiency in the Chromatographic Analysis and in the Electrochemical Analysis?

Antioxidants are food additives largely employed to inhibit oxidative reactions in foodstuffs rich in oils and fat lipids, extending the shelf life of foodstuffs and inhibiting alterations in color, flavor, smell, and loss of nutritional value. However, various research has demonstrated that the inadequate use of synthetic antioxidants results in environmental and health problems due to the fact that some of these compounds present toxicity, and their presence in the human body, in high concentrations, is related to the development of some cancer types and other diseases. Therefore, the development of analytical methods for identifying and quantifying synthetic antioxidants in foodstuffs is fundamental to quality control and in ensuring consumer food safety. This review describes the recent chromatographic and electrochemical techniques used in the detection of synthetic phenolic antioxidants in foodstuffs, highlighting the main characteristics, advantages and disadvantages of these methods, and specific typical features, which include extraction methods for sample preparation and materials used in the working electrode construction, considering chromatographic and voltammetric methods, since these specific features influence the efficiency in the analysis.     

Kinetic Deuterium Isotopic Effects in the Thermal Decomposition of β-Cyclodextrin hydrates

The apparent kinetic parameters of the thermal decomposition of the -cyclodextrin–heavy water complex were obtained from dynamic TG analysis. Various calculation methods were used and the results compared with those of the ordinary water complex. The processes of decomposition occur as zero order reactions with an activation energy of 65.7 and 69.7 kJ/mole respectively, calculated for one mole of water and heavy water. The parameters were used to estimate the kinetic deuterium isotopic effect.     

Kinetic patterns in the formation of nanosized manganese–manganese oxide systems

Transformations in nanosized manganese films are studied by means of optical spectroscopy, microscopy, and gravimetry at different film thicknesses (d = 4–108 nm) and temperatures of heat treatment (T = 373–673 K). It is found that the kinetic curves of conversion are satisfactorily described in the terms of linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference is measured for Mn and MnO films, and photo EMF is measured for Mn–MnO systems. An energy band diagram is constructed for Mn–MnO systems. A model for the thermal transformation of Mn films is proposed that includes stages of oxygen adsorption, the redistribution of charge carriers in the contact field of Mn–MnO, and manganese(II) oxide formation.     

Prospect of Thiazole-based γ-Peptide Foldamers in Enamine Catalysis: Exploration of the Nitro-Michael Addition

As three-dimensional folding is prerequisite to biopolymer activity, complex functions may also be achieved through foldamer science. Because of the diversity of sizes, shapes and folding available with synthetic monomers, foldamer frameworks enable a numerous opportunities for designing new generations of catalysts. We herein demonstrate that heterocyclic γ-peptide scaffolds represent a versatile platform for enamine catalysis. One central feature was to determine how the catalytic activity and the transfer of chiral information might be under the control of the conformational behaviours of the oligomer.     

Mechanistic Study of Catalysis in the Mizoroki–Heck Reaction with Anhydrides of Aromatic Acids

A kinetic study of reaction of alkene arylation by anhydrides of aromatic acids (modified Mizoroki–Heck reaction) was carried out using differential selectivity as the main measured parameter. The results obtained under conditions of competition between a pair of alkenes or a pair of aromatic anhydrides point to the occurrence of the reaction via a homogeneous mechanism of catalysis analogously to a conventional variant of reaction with aryl halides as arylating reagents. The hypothesis that the active catalyst is homogeneous agrees with the results of kinetic studies of processes of catalyst formation and deactivation.     

How Long Have Nonlinear Effects Been Known in the Field of Catalysis?

The similarities and differences between nonlinear effects in asymmetric synthesis (see diagram), predicted 60 years ago by W. Langenbeck, and the long-known amplification phenomenon in stoichiometric reactions with chiral starting materials are discussed.     

Kinetic features of short-time polymerization of isoprene in the presence of supported titanium–magnesium catalyst

Short-time polymerization of isoprene under the action of supported titanium–magnesium catalyst is carried out. The pulsation mixing of the reagent flows and the unit design features allow one to reduce the average residence time of reagents in the reaction zone and to study the first 0.7 s of the isoprene polymerization. It is found that, very early in polymerization, the propagation of polyisoprene macromolecules proceeds on the surface of the primary aggregates of catalyst particles characteristic of a high trans-1,4 specificity via the “living” mechanism with a high rate. Furthermore, the fragmentation of the initial aggregates of the catalyst particles occurs, which results in formation of new polymerization centers, a decrease in the average molecular masses of polyisoprene, and a broadening of the polymer MMD. The results are explained by the existence of a range of the kinetic continuity of the rapid initiation stage and several subsequent stages of macromolecule propagation, followed by a significant decrease in the chain propagation rate constant compared to the initiation constant.