Parametric analysis of kinetic models. I. The simplest autocatalytic oscillator

A series of mechanisms allowing oscillations and differring in the form of their buffer steps (step 3)

Parametric analysis of kinetic models. 9. Catalytic triggers with diffusion exchange steps

Bimetallic catalysts consisting of Ru–Fe prepared on SiO₂ and carbon (sibunit) supports were found to be catalytically active and selective in the formation of C₄-aldehydes and alcohols in hydroformylation of propylene at 433 K and 2 atm. of CO+H₂+C₃H₆ (111). The addition of Fe to Ru altered the activity of monometallic Ru catalyst and favored the hydrogenation of CO to methanol.     

Parametric analysis of kinetic models. XIV. Autocatalytic trigger and oscillator in a flow system

In a flow catalytic reactor with an autocatalytic trigger as a kinetic subsystem, the conditions have been found, in which oscillations appear. Some peculiarities of the kinetic model dynamics, where the kinetic subsystem is an autocatalytic oscillator, are investigated.     

Parametric analysis of kinetic models, 8. Two-center catalytic oscillators

The results of parametric analysis for a kinetic model of CO oxidation reaction on two types of active centers of Pt are given. The local bifurcation curves are constructed for every type of center. The regions with self-oscillations are singled out in a plane (p_CO, T). A sum of rate oscillations on every center can have a quasi-chaotic character.     

Parametric analysis of kinetic models, XII. Influence of the intensity of diffusion exchange

Some nonlinear mechanisms of catalytic reactions involving diffusion exchange between two types of active centers are considered. Dependences of stationary kinetic characteristics on the intensity of diffusion exchange are obtained. A region of self-oscillation is singled out on the parametric portrait of the kimetic model.     

Parametric analysis of kinetic models, XI. Influence of the number of active sites

The influence of active sites number on the stationary characteristics of kinetic models is analyzed for some nonlinear schemes of conversion on catalyst surface. Mechanisms involving one and two types of active sites are considered. A possibility of critical effects is shown.     

Principal component analysis of kinetic models

An eigenvalue–eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for several species of a reacting system at several time points. The main advantage of this method lies in its ability to reveal those parts of the mechanism which consist of strongly interacting reactions, and to indicate their importance within the mechanism. Results can be used to solve three general kinetic problems. Firstly, an objective condition for constructing a minimal reaction set is presented. Secondly, the uncovered dependencies among the parameters are shown to confirm or deny validity of quasi-steady-state assumptions under the considered experimental conditions. Thirdly, taking into account only sensitivities of observed species, the analysis is used to yield error estimates on unknown parameters determined from the experimental observations, and to suggest the parameters that should be kept fixed in the estimation procedure. To illustrate we chose the well-known hydrogen–bromine reaction and the kinetics of formaldehyde oxidation in the presence of CO.     

A simple model of a kinetic heterogeneous catalytic oscillator

A model of a heterogeneous catalytic oscillator with minimum number of kinetic parameters is proposed. Feedback in the oscillator is the dependence of the rate constant of one of the steps on the filling of the surface of the catalyst by adsorbed particles.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 152–154, March–April, 1992.     

Parametric Analysis of Kinetic Models. Xiii. Catalytic Trigger in a Flow System

The thickness of the concentrated layer in the MSSP suspensions, which is sufficient to initiate phase transition into supramolecular crystals, has been experimentally determined and calculated. When the electrostatic repulsion predominates over molecular attraction, the transition occurs only if gravitational forces, which virtually act as molecular attracting forces, are involved.     

催化动力学光度法测定青霉素G及其机理研究

研究了在青霉素G存在下双氧水氧化苋菜红的褪色反应,建立了催化动力学光度法测定微量青霉素G的方法.方法线性范围为0.20～4.00μg/mL,回归方程y=-0.015p(μg/mL)+0.311,r=0.9998;方法线性范围为4.00～50.0μg/mL,回归方程y=0.001p(μg/mL)+0.280,r=0.99...     

顺序注射催化动力学光度法测定织物和室内空气中痕量甲醛

在磷酸介质中 ,甲醛可以催化溴酸钾氧化　花青的反应使其退色 ,据此建立了顺序注射催化动力学光度法测定织物和室内空气中痕量甲醛的新方法。方法的线性范围 0 .5～ 7.0 μg mL ,检出限 0 .1 μg mL。用于树脂整理特殊织物和室内空气中痕量甲醛的测定 ,回收率在 97.0 %～ 1 0 5 .0 %之间。     

Application of complex reaction kinetic models in thermal analysis

The complexity of the phenomena which arise during the heating of the various substances seldom can be described by a single reaction kinetic equation. As a consequence, sophisticated models with several unknown parameters have to be developed. The determination of the unknown parameters and the validation of the models requires the simultaneous evaluation of whole series of experiments. We can accept a model and its parameters if, and only if we get a reasonable fit to several experiments carried out at different experimental conditions. In the field of the thermal analysis the method of least squares alone seldom can select abest model or abest set of parameter values. Nevertheless, the careful evaluation of the experiments may help in the discerning between various chemical or physical assumptions by the quality of the corresponding fit between the experimental and the simulated date. The problem is illustrated by the thermal de-composition of cellulose under various experimental conditions.This research program was funded by the National Science Foundation (grant INT 8914934), the US Hungarian Science and Technology Joint Fund (grants 90b-22 and 93b-375), the Hungarian National Research Fund (OTKA, grant 3077/91) and the Coral Industries Endowment.     

Assisted desolvation as a key kinetic step for crystal growth

The crystallization of materials from a supersaturated solution is a fundamental chemical process. Although several very successful models that provide a qualitative understanding of the crystal growth process exist, in most cases the atomistic detail of crystal growth is not fully understood. In this work, molecular dynamics simulations of the morphologically most important surfaces of barite in contact with a supersaturated solution have been performed. The simulations show that an ordered and tightly bound layer of water molecules is present on the crystal surface. The approach of an ion to the surface requires desolvation of both the surface and the ion itself leading to an activated process that is rate limiting for two-dimensional nucleation to occur. However, desolvation on specific surfaces can be assisted by anions adsorbed on the crystal surface. This hypothesis, corroborated by crystallization and scanning electron microscopy studies, allows the rationalization of the morphology of barite crystals grown at different supersaturations.     

催化动力学荧光光谱法测定L-半胱氨酸

在pH 1.1的HCl-KCl缓冲溶液中,L-半胱氨酸可以催化溴酸钾氧化灿烂甲酚蓝的反应,使其荧光淬灭,据此建立了一种催化荧光动力学测定L-半胱氨酸的新方法.系统研究了不同环境介质与干扰物质对荧光强度的影响.方法的线性范围0.032～1.60 μg/mL,检出限为0.01 μg/mL,RSD＜5.7%.方法简便快捷,体系稳定.用于果汁与蜂蜜中L-半胱氨酸的测定,回收率在99.3%～104.0%之间.     

Modeling cellobiose hydrolysis with integrated kinetic models

The enzyme cellobiase Novozym 188, which is used for improving hydrolysis of bagasse with cellulase, was characterized in its commercial available form and integrated kinetic models were applied to the hydrolysis of cellobiose. The specific activity of this enzyme was determined for pH values from 3.0–7.0, and temperatures from 40–75°C, with cellobiose at 2 g/L. Thermal stability was measured at pH 4.8 and temperatures from 40–70°C. Substrate inhibition was studied at the same pH, 50°C, and cellobiose concentrations from 0.4–20 g/L. Product inhibition was determined at 50°C, pH 4.8, cellobiose concentrations of 2 and 20 g/L, and initial glucose concentration nearly zero or 1.8 g/L. The enzyme has shown the greatest specific activity, 17.8 U/mg, at pH 4.5 and 65°C. Thermal activation of the enzyme followed Arrhenius equation with the Energy of Activation being equal to 11 kcal/mol for pH values 4 and 5. Thermal deactivation was adequately modeled by the exponential decay model with Energy of Deactivation giving 81.6 kcal/mol. Kinetics parameters for substrate uncompetitive inhibition were: Km=2.42 mM, V _max=16.31 U/mg, Ks=54.2 mM. Substrate inhibition was clearly observed above 10 mM cellobiose. Product inhibition at the concentration studied has usually doubled the time necessary to reach the same conversion at the lower temperature tested.     

荧光黄的示波极谱特性研究及其在催化反应-示波极谱分析中的应用

在pH4.9HOAc-NaOAc缓冲溶液中, 荧光黄于-0.50V(vs.SCE)产生一灵敏的单扫描示波极谱波。在100℃弱碱性介质中, 铱(IV)对KIO~4氧化荧光黄这一反应具有强烈催化作用。本文研究了荧光黄的示波极谱行为及利用该催化反应测定痕量铱的各种影响因素,拟定了铱的催化反应-示波极谱分析新方法, 它们的检出限和测定范围分别为0.04ng/mL和0.08-8.0ng/mL。     

Catalytic kinetic simultaneous determination of iron, silver and manganese with the Kalman filter by using flow injection analysis stopped-flow spectrophotometry

A catalytic differential kinetic method with Kalman filter for the simultaneous determination of multi-component is described. The oxidization of Rhodamine B (RB) by potassium periodate in a slightly acid solution is a slow reaction. But iron(III), silver(I) or manganese(II) has a differential catalytic effect on the oxidation reaction of RB in the presence of 1,10-phenanthroline as the activator. So iron, silver and manganese can be simultaneously determined by measuring the decreasing absorbance of the dye (RB) at 555 nm. A flow injection analysis stopped-flow spectrophotometric system with a microcomputer performs the determinations. This method has been applied to determining iron, silver and manganese of alloy samples with satisfactory results.     

Catalytic kinetic resolution of cyclic secondary amines

The catalytic resolution of racemic cyclic amines has been achieved by an enantioselective amidation reaction featuring an achiral N-heterocyclic carbene catalyst and a new chiral hydroxamic acid cocatalyst working in concert. The reactions proceed at room temperature, do not generate nonvolatile byproducts, and provide enantioenriched amines by aqueous extraction.