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Oscillatory behaviour during methane oxidation over a cobalt foil has been studied using on-line mass-spectrometry and video recording of the colour of the catalyst surface. It was demonstrated that during oscillatory behaviour, periodic transitions of the catalyst surface from an oxidised state (dark colour) to a reduced state (light colour) occurred together with the variation of the catalyst temperature. Oscillations over the cobalt foil appeared at higher temperatures (860–950 °C), and had longer periods, in comparison with oscillatory behaviour which was observed earlier over a nickel foil. The application of TGA in combination with TPR experiments revealed the differences in nickel and cobalt redox properties which are responsible for the variation in the properties of the oscillations. Forced oscillations could be obtained in a low temperature region (700–860 °C), if bare chromel and alumel wires were spot-welded separately to the cobalt foil. It was shown that in this case the chromel wire induced oscillatory behaviour of the whole cobalt foil. Complicated mixed mode oscillations detected at higher temperatures were shown to be the result of the coupling of high frequency oscillations produced by the unshielded chromel–alumel thermocouple and low frequency oscillations appearing over the cobalt foil.

A simple and sensitive method is presented for the determination of dopamine with a nanoscale ceria ion-selective CMC (carboxymethyl cellulose) membrane electrode by means of the Belousov–Zhabotinsky oscillating chemical reaction. The electrode exhibits excellent potential response. If the concentration of dopamine is in the range of 4.9 × 10−5 to 2.4 × 10−7 mol · L−1, the change in oscillating amplitude is proportional to the concentration of dopamine, with a correlation coefficient of 0.9987 and a standard deviation of 0.17%. A recovery of 97.5–105.0% was obtained. Interference was also studied. The use of a nanoscale ceria ion-selective membrane-working electrode improved the sensitivity of the determination method.

A new organic substrate has been used to promote oscillations under batch conditions in the Briggs–Rauscher oscillating system. The new substrate, 1,4-cyclohexanedione (CHD), reacts with aqueous iodine via an enol mechanism. We discuss the effect of the initial concentrations, the temperature and chemical perturbations. In a definite range of concentrations long-lived oscillations with two significantly different frequency periods were observed. The low frequency parts are temperature-dependent while the high frequency oscillations do not show temperature dependence. The inhibitory effects of 1,4-hydroquinone and 1,4-benzoquinone on the oscillations and the kinetics of some important component reactions were studied to develop a model for the simulation of the observed oscillations.

A highly sensitive method for the determination of trace amounts of transition metal ions by use of sulfide in the Belousov–Zhabotinskii (B–Z) oscillating chemical reaction is proposed. The use of sulfide increased strongly the sensitivity of the B–Z reaction for transition metal ions, such as Ag + , Pb 2+ , Hg 2+ , Cd 2+ , Cu 2+ ,and Bi 3+ . Results showed that the variational ratio of oscillating period ( P R ) is linearly proportional to the negative logarithm of concentration of metal ions. The detection limit is down to 10 −12 mol L −1 . Various influencing factors on the determination were also examined.

The electro-oxidation of sulfide on a Pt electrode is found to exhibit both N-NDR (negative differential resistance) and HN-NDR (hidden negative differential resistance) types of oscillations, making it the first system known to be capable of supporting both types of nonlinear instabilities without changing electrolyte compositions. Six distinct oscillation windows are observed when the external current is adjusted as the control parameter. In addition, temperature also exhibits subtle influences on the observed reaction behavior, where varying the temperature from 30.0 °C results in more complicated oscillatory phenomena. Keywords: Electrochemical oscillations, Nonlinear instabilities, Sulfide, Platinum electrodes

An analytical method for the determination of alpha-naphthol (α-NP) is proposed by the sequential perturbation caused by different amounts of alpha-naphthol on the oscillating chemical system involving the Cu(II)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium with the aid of continuous-flow stirred tank reactor (CSTR). The method relies on the linear relationship between the changes in the oscillation amplitude of the chemical system and the concentration of alpha-naphthol. The use of the analyte pulse perturbation technique permits sequential determinations in the same oscillating system owing to the expeditiousness with which the steady state is regained after each perturbation. The calibration curve obeys a linear equation very well when the concentration of alpha-naphthol is over the range 0.034–530 umol/L ( r = 0.9991). Influences of temperature, injection points, flow rate and reaction variables on the oscillating system are investigated in detail and the possible mechanism of action of alpha-naphthol to the chemical oscillating system is also discussed. The method has been successfully used for the determination of α-naphthol in carbaryl hydrolysates.

In this paper, a named oscillation frequency spectrum (OFS) was developed for the frequency analysis of oscillating signal. Various complexing oscillating chemical reactions, which have been widely applied to analytical determination, were examined. The OFS extracted frequency information of these systems successfully and distinguished their respective frequency characteristics clearly. The details were such that the Belousov-Zhabotinskii (B-Z) system had three frequency peaks and the Cu(II)-catalyzed system had two. Every periodic signal had a special OFS. Even if the frequency values of two different signals were identical, their OFS figures were distinct. The OFS realized the extraction and calculation for the multifrequency characteristic of oscillating chemical system accurately. It followed that OFS could be used to analyze the frequency of periodic signal with accuracy and was suitable for many areas. Copyright © 2006 John Wiley & Sons, Ltd.

The reaction of bromate ion with malic acid in aqueous H2SO4 catalyzed by a tetraazamacrocyclic copper(II) complex exhibits oscillatory behavior. This complex contains an unsaturated macrocyclic ligand, 5,7,7,12,14,14-hexemethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The reactions were monitored both spectrophotometrically and potentiometrically. It was found that the oscillation period (tp) is dependent on the initial concentrations of malic acid or H2SO4 but is independent of the initial concentrations of NaBrO3. The experimental results indicate that acrylonitrile, H2O2, vitamin C, glucose or CCl4 present in the system can inhibit the oscillations. A tentative mechanism is proposed.

A simple analytical method for the determination of p-nitrobenzene-azo-naphthol was proposed by a sequential perturbation with different amounts of p-nitrobenzene-azo-naphthol on an oscillating chemical system. The method involves a Cu(II)-catalysed oscillating reaction between hydrogen peroxide and sodium thiocyanate in alkaline medium with the aid of continuous-flow stirred tank reactor (CSTR). A good linear relationship between the changes, oscillation amplitude or/and period, and the concentration of p-nitrobenzene-azo-naphthol was obtained. The use of analyte pulse perturbation technique provides a possibility of sequential determination in a same oscillating system, due to a new steady state that reappeared rapidly after each perturbation. The calibration curve fits a linear equation very well when the concentration of p-nitrobenzene-azo-naphthol ranging from 5.2×10−7 to 3.3×10−3M. Influence of temperature, injection point, flow rate and reactants variables on this system were investigated in detail.

We have investigated the effect of solution composition on the pattern of traveling wave formation in self-oscillating gel in which a metal catalyst for the Belousov-Zhabotinsky(BZ) reaction is covalently bonded to the gel matrix. The reaction solution contains all reactants for the BZ reaction except the catalyst. The gel was synthesized by the co-polymerization of N-isopropylacrylamide(NIPAAm) and Ru(bpy)32+ catalyst monomer. To vary the composition of the environmental solution for the oscillation reaction, we added a small amount of hydroquinone to the BZ solution since hydroquinone is a good reagent inducing a characteristic wave pattern in the BZ type oscillation system. The experimental results show that the pattern of wave formation in the self-oscillating gel is influenced greatly by a change of the environmental condition of the solution composition for the oscillation reaction without other environmental change such as temperature and pH.

A new analytical method for the determination of uric acid (UA) by the perturbation of UA on the Belousov–Zhabotinsky oscillating reaction is proposed. The method is based on the linear relationship between the changes in the oscillating period and the concentration of UA. The calibration curve is linear over the range of 2.0 × 10 −5 to 5.0 × 10 −4 M, with a detecting limit of 3.28 × 10 −6 M. The method features good precision (R.S.D.: 3.59%) and excellent throughput (10 samples h −1 ). The possible mechanism of the perturbation of UA on the oscillating reaction is discussed.

A simple and reliable kinetic method for the determination of hesperidin (Hesp) is developed. It is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system which is in a stable non-equilibrium stationary state close to the bifurcation point. The Bray-Liebhafsky oscillatory reaction is used as the matrix system. The response of the matrix to perturbations by different concentrations of Hesp is followed by using a Pt electrode. A linear relationship between maximal potential shift and the logarithm of Hesp concentrations is obtained between 7.5 and 599.4 microg mL-1. The limit of detection is 0.65 microg mL-1. The described procedure has been successfully applied to the determination of Hesp from different sources (capsules, industrial and hand-squeezed orange juice, and white wine).

It was found for the first time that the acid hydrolysis of 2,5-dimethylfuran in water-ethanol solutions has self-oscillating character. Oscillations in the concentrations of the two products 2,5-hexanedione and an unidentified compound X were detected by GLC. The ranges of hydrochloric acid and ethanol concentrations in which these oscillations appear were determined. It is suggested that the formation of compound X results from tautomeric transformations of 2,5-hexanedione under the reaction conditions. Quantum-chemical calculations showed that the possible tautomers are formed with equal probability.

This paper reports a new methodological approach for investigating oscillating chemical reactions using simple and fast analytical information by measuring the conductivity of the solution. Although this technique is very common, and one of the simplest methods among the analytical techniques, however no work has been reported so far using this method for studying an oscillating system. For measuring conductivity, we use the oscillating system of H2O2–KSCN–CuSO4–NaOH. Results indicate that the conductivity of the system fluctuates during the oscillating reaction. The oscillating conduction of this system was studied by changing the concentration of species involved in the oscillating reaction. Results indicate that the oscillating behaviour is varied by changing the concentration of the species.

The chlorine dioxide-iodine-malonic acid oscillating reaction produces Turing patterns when operated in open spatial reactors. In the same operating conditions, the chlorine dioxide-iodide bistable reaction leads to spatial bistability between two steady states that do not break the symmetry of boundary conditions. We develop a system combining these two properties. Phase diagram studies show that the Turing pattern region cannot be generically made to interact with the phenomenon of spatial bistability. In the spatial bistability region, stationary pulses and complex transient domain patterns are observed, a new phenomenon for the chlorite-iodide driven systems. These have no connection with the previously observed Turing patterns. We propose a systematic design method to produce permanent domain patterns in systems exhibiting spatial bistability.

This communication reports, for first time, how the simultaneous record of the solution potential and sonocurrent transient on a working electrode at fixed potential can provide meaningful information on the oscillatory mechanism for oscillating reactions driven in a highly passivated environment. The advantages of ultrasonically enhanced chronoamperometric analysis in comparison to potentiometry were tested. Those techniques were used for the study of the effect of isobutylmethyl ketone on the uncatalyzed class of bromate oscillating chemical reaction (UBO). This communication presents experimental results that support the hypothesis that methyl ketones consume the molecular bromine that is formed during the UBO reaction. Keywords: Oscillating reactions, Chronoamperommetry, Ultrasound

We have studied the catalytic oxidation of CO on Pd(1 0 0) at atmospheric pressures, using a combined flow reactor and scanning tunneling microscope (STM). By switching from a CO-rich flow to an O2-rich flow, and vice versa, we could reversibly oxidize and reduce the surface, as we have observed with the STM. Both during the initial oxidation and during the catalytic reaction on the oxide, the surface became rough. Coinciding with the formation of the palladium oxide there was a step up in the CO oxidation rate. Whereas the reaction rate on the metallic surface followed traditional Langmuir–Hinshelwood kinetics, the reaction rate on the oxide was proportional to the CO-pressure and did not depend on the O2-pressure. We suggest that the high reaction rate on the oxide resulted from the low stability of the oxide, making it highly reactive, and that the reaction followed the Mars–Van Krevelen mechanism, in which the oxide is continually consumed and reformed. The switching between the metallic surface and the oxide showed significant hysteresis in the CO-pressure for O2-rich conditions. This resulted in a CO-pressure window where reaction was stable both on the metal and on the oxide. We have observed that the reaction switched spontaneously between these branches, leading to oscillations in the reaction rate. Our interpretation is in strong disagreement with well-established models for CO oxidation on Pt-group metal surfaces. � 2004 Elsevier B.V. All rights reserved.

The bromate-1,4-cyclohexanedione-ferroin oscillating reactions are uncovered to support two types of wave activities, in which spontaneous formation of circular waves has been achieved after the disappearance of initial waves. The induction period of the revival wave is typically above 10 hours and its dependence on the initial concentrations of reactants is qualitatively different from that of initial waves. In addition to their differences in propagating speed and wavelength, the initial waves and the revival patterns have different colors, suggesting that different reaction mechanisms are involved in the formation of these spatiotemporal behaviors. Our experiments further show that the addition of hydroquinone to the reacting system can significantly shorten the induction time of the revival wave, which implicates that hydroquinone is not only a product in the bromate-1,4-cyclohexanedione-ferroin oscillating reaction but also plays a critical role in the following reactions.

A hierarchy of models of chemically reactive low-pressure plasma was considered. On the basis of the Field–Noyes model as a formal set of homogeneous reactions initiated by plasma-generated reactive particles, the possibility of complex dynamic oscillating reaction modes was demonstrated. The form of the solution of the set of equations was analyzed for the process in the afterglow zone at excess concentration of the plasma-generated reactant and with allowance made for the reactant consumption in chemical reactions, and also for the process in the plasma zone with due regard to chemical feedback. It was shown that the form of the solution is determined by the character of chemical feedback.

A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8x10(-8) mol dm(-3) and 9.1x10(-6) mol dm(-3), we found a linear dependence of the maximal potential shift, DeltaE(m), on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of +/-5%. The detection limit is 3.6x10(-8) mol dm(-3). The amount of required sample can be as small as 10 muL.

The stoichiometric relations of complex reaction networks were discussed with the general theory of stoichiometric number introduced and developed by Horiuti et al. Horiuti introduced the concept of reaction route in the theory, in which the reaction route was expressed by a set of stoichiometric numbers. The theory was applied to analyses of the stoichiometries in the reaction network of the 11 pseudo-elementary reactions (steps) of the Belousov–Zhabotinski (BZ) reaction and its reduced mechanism called the amplified Oregonator. Both of the mechanisms were developed by Noyes et al. for analysis of the oscillatory phenomena of the BZ reaction. The amplified Oregonator was concluded sufficiently to describe the stoichiometries of the original network of 11 steps by using the general theory of stoichometric number. In comparison of these analyses of the stoichiometries in the above two mechanisms, a criterion for preserving overall stoichiometry in reduced mechanisms was introduced.

Based on the continuous wavelet transform (CWT), three types frequency spectra, wavelet frequency spectrum (WFS), point frequency spectrum (PFS) and time frequency spectrum (TFS), were developed. Two data sets were simulated and treated with the proposed spectra, the results indicated that WFS could extract the frequency information, which was like Fourier analysis but more accurate, PFS could obtain the frequency at any moment, TFS could show frequency change with time. These abilities of PFS and TFS were impossible for Fourier analysis. An oscillating chemical signal was processed with WFS and TFS. From the processed results, two points could be learned about the oscillating chemical reaction: one was the oscillating chemical reaction was a mixture one including two or more complex kinetics processes, the velocity of the switch from the reduced state (RS) to the oxidized state (OS) was faster than the reverse switch (from OS to RS); the other was increase of KBrO 3 could decrease the velocities of both switches, which led to the oscillating period became longer.

Electrochemical quartz crystal microbalance (EQCM) has been employed to study the potential oscillatory mechanism for the IO3− reduction accompanying periodic hydrogen evolution. The new experimental results that were obtained by in situ EQCM monitoring clearly demonstrate the all key steps involved in the oscillation: the diffusion-limited depletion of IO3− by reduction, the formation, growth and departure of hydrogen bubbles on the surface, and the convection-induced replenishment of IO3− by the hydrogen evolution. In addition to the frequency response to the surface mass change as reported in the literature, our study first shows that simultaneous frequency responses to the changes of density and viscosity in the diffusion layer during the oscillation can also provide meaningful and even decisive information on the oscillatory mechanism for the oscillators involving the coupling of electrochemical reactions with diffusion and convection mass transfer. Keywords: EQCM, IO3-, Reduction, Hydrogen evolution, Potential oscillations, Mechanism

Applications of NMR imaging to studies of chemical reactions including polymerisation reactions and the Belousov-Zhabotinsky oscillating reaction are considered. Publications concerning applications of NMR imaging to studies of the temperature and electric current density distributions in various specimens are discussed. NMR investigations of hyperpolarised gases and gases with equilibrium nuclear spin polarisation are described. NMR imaging studies of solids (in particular, polymers and elastomers) are briefly outlined. The bibliography includes 275 references.

Using the Monte Carlo technique, we simulate kinetic oscillations in CO oxidation occurring on nm-sized supported Pt particles via the conventional Langmuir–Hinshelwood mechanism and surface oxide formation and removal. Incorporating cooperative effects into the oxide growth mode, we demonstrate that the oscillations may be accompanied by remarkable segregation between oxide and CO. During oscillations, the maximum CO coverage may be appreciably smaller that that at saturation. These findings are in line with recent transient Fourier transform infrared spectroscopy measurements (Fanson, P.T., Delgass, W.N., Lauterbach, I., J. Catal. 204 (2001) 35) indicating that during oscillations on Pt/SiO2 the CO coverage is relatively low and the shift of the stretching frequency of linearly bonded CO is nearly negligible.

The volume of gaseous oxygen produced during the Briggs−Rauscher (BR) oscillating reaction with acetone was measured. The rates of oscillatory oxygen evolution were calculated and the effects of stirring rate and addition of acrylamide on the oscillations were studied. The dynamic behavior of the modified BR reaction was modeled by mechanisms suggested by Noyes and Furrow (J. Am Chem. Soc. 1982, 104, 45) and De Kepper and Epstein (J. Am. Chem. Soc. 1982, 104, 49), supplemented by the physical processes of the iodine and oxygen interphase transport. The calculated oscillatory parameters are in satisfactory agreement with experiment.

The oscillatory features of a novel type B–Z type oscillator, fructose [F] + oxalic acid [OA]+Ce 4+ +BrO 3 − +H 2 SO 4 has been investigated. The induction time is found to be usually small or negligible. Both single frequency oscillations and two oscillatory states separated by a time-pause are observed. Oscillations occur between two critical limits of [F] and [OA]. A tentative mechanism has been suggested which involves both Br − ion control and free radical control. Computer simulation correctly predicts some of the oscillatory features such as (i) time of initiation, (ii) critical limits of [OA] and (iii) stoppage of oscillations by higher [Br − ], confirming the primary role of Br − control mechanism.

This paper is a preliminary study of time–frequency behavior of homogenous Belousov–Zhabotinsky reaction in a batch reactor. A series of measurements performed for a variable concentration of the reaction substrates led to the conclusion that there exists time-dependency of an instantaneous frequency of fundamental frequency and harmonics and of electrode potential fluctuations generated during the process discussed. The Short Time Fourier Transformation (STFT) was proposed for analyzing electrode potential registers. On the basis of STFT analysis a decrease in frequency of oscillations of exponential character has been postulated.

Revival waves, which emerge spontaneously long after the oscillatory bromate–1,4-cyclohexanedione–ferroin reactions become quiescent, are found susceptible to the illumination of visible light. Depending on the intensity and the duration of the light perturbation, an illumination can drive the system either to a reduced reaction state with a high concentration of ferroin, or to an oxidized state with a high concentration of ferriin. When hydroquinone, a main product from 1,4-cyclohexanedione oxidation, is used to gradually replace 1,4-cyclohexanedione as the reductants, the induction period of the formation of revival waves is shortened significantly; however, there is no clear difference in their photosensitivity. These new experimental results suggest that the observed photosensitivity is determined by the photochemistry of the products of hydroquinone.

The complexity of oscillating chemical reactions makes difficult a direct calorimetric study of them. It is more advantageous to carry out studies of the component steps and then try to put the parts together. Here, a mass-flow heat conduction calorimeter was used to study component reactions of two of the principal chemical oscillators. The studied reactions were: the net reaction of the inorganic set of the Belousov-Zhabotinsky reaction BrO3 -+4Ce3++5H+D4≤;8805;Ce4++HOBr+2H2O), and the Dushman reaction IO3 -+5I-+6H+≤;8805;3I2+3H2O), which is a component of the Bray-Liebhafsky oscillator. The experimental values of the enthalpies of these two reactions are reported in this work.

Thermokinetic oscillations obtained during the heterogeneous catalytic oxidation of methanol on Pd/LiAl5O8 in a dynamic calorimeter were characterized by an overall activation energy. This parameter was determined using the minimum and maximum values of the temperature oscillations. Using bifurcation diagrams with oxygen or methanol as bifurcation parameters. E values for all heating loss laws were calculated which are within the range for heterogeneous catalytic oxidation reactions. The obtained results have been discussed.

International audience; Oscillating chemical reactions, encapsulated within artificial vesicles have been demonstrated as a powerful analogy of living cells for the investigation of chemical communication and morphogenesis. However, little is understood with regards to the influence of confinement on the reactivity of such systems. Herein, the effect of confinement on the Belousov–Zhabotinsky (BZ) oscillating reaction in bulk solution, (employing ferroin as a catalyst and malonic acid as the organic substrate) is investigated using scanning electrochemical microscopy (SECM) toward different insulating surfaces such as glass, silanized glass, or PTFE. An unexpected increase in the amplitude of the BZ reaction at a tip–substrate distance of ∼12–15 μm is observed. By simulating different reaction mechanisms, from simple EC′ catalysis to more sophisticated Oregonator or even an 11-reaction scheme, it is shown that such behavior reveals the intervention of redox catalysis processes and particularly the short-lived highly reactive radical intermediate BrO2• indirectly detected at micromolar concentrations. The reinspection of the EC′ mechanism shows that the homogeneous catalysis route is confirmed and kinetically characterized from SECM toward an insulating substrate, with promising potentiality in many systems. More specifically to the complex chemical case of BZ reactions, the mechanism is understood from the envelope curves of the oscillations, which are assessed in the absence of the oscillation (absence of organic substrate).

Stimuli-responsive polymer gels and their application to smart materials have been widely studied. On the other hand, as a novel biomimetic gel, we developed gels with an autonomous self-oscillating function like a heart muscle, which was firstly reported in 1996. We designed the self-oscillating polymers and gels by utilizing the oscillating reaction, called the Belousov-Zhabotinsky (BZ) reaction as a chemical model of the TCA cycle. The self-oscillating polymer is composed of a poly(N-isopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently bonded. In a closed solution containing the reactants other than the catalyst, the polymer gel undergoes spontaneous cyclic swelling-deswelling changes without any on-off switching of external stimuli. Their potential applications include several kinds of functional material systems, such as biomimetic actuators and mass transport surface. Here recent progress on the novel polymer gels is introduced.

A new method based on the inhibitory effects of antioxidants on the oscillations of the hydrogen peroxide, acidic iodate, malonic acid, and Mn(II)-catalyzed system (known as the Briggs-Rauscher reaction), was used for the evaluation of antioxidative capacity. With this method, which works near the pH of the fluids in the stomach (pH approximately 2), a group of natural compounds present in fruits and vegetables or in medicinal plants assumed to have antioxidant capacity, was tested successfully. The aim of the present study is to evaluate the antioxidative properties of some active principles contained in vegetables and aromatic plants, namely, cynarin (from Cynara scolymus), rosmarinic acid (from Rosmarinus officinalis), echinacoside (from Echinacea species), puerarin (from Pueraria lobata), and oleuropein (from Olea europea). Also studied with the Briggs-Rauscher reaction method was the antioxidant activity of cyanidin 3-O-beta-glucopyranoside (from Citrus aurantium) in order to compare the results with those obtained by other methods. The conclusions on the dependency of the antioxidative activity on the pH of the testing system are given.

A model for the Briggs–Rauscher reaction mechanism with four intermediates and seven steps is proposed by simplifying the model of De Kepper and Epstein [J. Am. Chem. Soc. 104, 49 (1982)]. Assigning suitable rate constants for the steps of the simplified model, we obtain numerical results for the nonlinear dynamic behaviors such as oscillations, limit cycle, multistability, and inverse regulation of the iodine concentration. The results are compared with experiments and other previous models. The comparison shows that the present simplified model expresses the nonlinear dynamic behaviors better than the previous models.

The Briggs-Rauscher (BR) oscillating reaction in mixed 20% EtOH/H2O (v/v) medium is studied together with the inhibitory effects by the addition of hydroalcoholic solutions of antioxidants on its oscillatory regime. As in aqueous BR mixtures, the inhibitory effect consists of an immediate cessation of oscillations, an inhibitory time that linearly depends on the concentration of the antioxidant added, and subsequent regeneration of oscillations. The effects of several water-insoluble and water-soluble antioxidants were investigated: at a parity of concentration of antioxidant added, inhibition times in the mixed EtOH/H2O medium are 2–3 times lower than those reported previously in aqueous solution. However, the mechanism of the BR reaction, as far as that of the inhibitory effect, seems to be the same in either aqueous or mixed medium. The findings reported and discussed here are an indication that the analytical procedure to assess the activity of free radical scavengers based on the BR reaction can be extended to lipophilic antioxidants.

We present Monte Carlo simulations of kinetic oscillations in the CO–O 2 reaction occurring on a (1 0 0) facet of a nm-sized supported Pt particle. The model includes the conventional Langmuir–Hinshelwood mechanism of CO oxidation and CO- and O-induced restructuring of the facet. The facet size is varied from 50×50 to 5×5. With decreasing size, oscillations become more irregular. More or less regular oscillations accompanied by formation of CO islands are found for the sizes down to 15×15. Practically, this means that for observation of such oscillations the particle diameter should be above ≃4 nm. These findings are in agreement with available experimental data.

Self-oscillation of polymer chains in an aqueous solution has been achieved. The ruthenium catalyst for the Belousov-Zhabotinsky reaction was polymerized by using N-isopropylacrylamide and dissolved into the solution containing the BZ substrates. Periodical soluble-insoluble changes of the polymer chain were spontaneously induced by the BZ reaction. The conformational oscillations of the polymer were measured as the optical transmittance changes of the solution. This is the first report that rhythmical and reversible soluble-insoluble changes of polymer chains are realized under constant and homogeneous conditions. The transducing system from chemical energy of the BZ reaction to optical information has been constructed.

We present Monte Carlo simulations of kinetic oscillations in the CO–O2 reaction occurring on nm-sized supported catalyst particles. The model used includes the conventional Langmuir–Hinshelwood mechanism of CO oxidation and oxide formation and removal. The analysis is focused on such aspects as CO supply via the support, role of this supply in synchronization of oscillations on adjacent catalyst particles, and cooperative effects in the oxide formation.

Several new organic substrates have been found to promote oscillations in batch conditions in the Briggs−Rauscher oscillating system. The new substrates, crotonic acid, acrylic acid, anisole, and p-nitrophenol, react with iodine (I) by either addition or substitution reactions. Rate constants for reactions of these four compounds with HOI have been determined. Previously known substrates have active methylene hydrogens and react with I2 via an enol mechanism. Some type of active reduction of HIO2 to HOI (other than by iodide) must be included in the mechanism to allow the simulation of oscillations with the new substrates.

Experimental observations of temporal dynamics in the electrocatalytic oxidation of methanol (CH3OH) on a polycrystalline platinum electrode are reported. Hidden negative differential resistance (HNDR) and instabilities of the system were investigated by means of an electrochemical impedance spectrum analysis and potential oscillations under galvanostatic control. This result could be applied for a direct methanol fuel cell (DMFC) with higher energy efficiency.

Experimental studies employing surface science methods indicate that kinetic oscillations, chaos, and pattern formation in heterogeneous catalytic reactions often result from the interplay of rapid chemical reaction steps and relatively slow complementary processes such as oxide formation or adsorbate-induced surface restructuring. In general, the latter processes should be analysed in terms of theory of phase transitions. Therefore, the conventional mean-field reaction–diffusion equations widely used to describe oscillations in homogeneous reactions are strictly speaking not applicable. Under such circumstances, application of the Monte Carlo method becomes almost inevitable. In this review, we discuss the advantages and limitations of employing this technique and show what can be achieved in this way. Attention is focused on Monte Carlo simulations of CO oxidation on (1 0 0) and (1 1 0) single-crystal Pt and polycrystal Pt, Pd and Ir surfaces and of NO reduction by CO and H2 on Pt(1 0 0). CO oxidation on supported nanometre-sized catalyst particles and NO reduction on composite catalysts are also discussed. The results show that with current computer facilities the MC technique has become an effective tool for analysing temporal oscillations and pattern formation on the nanometre scale in catalytic reactions occurring on both single crystals and supported particles.

A novel and convenient method with good selectivity and high sensitivity for the determination of hydroquinone (HQ) based on the Belousov–Zhabotinskii (B–Z) oscillating chemical reaction has been presented. The optimum condition for the determination has also been investigated. In the B–Z reaction system, when the sample was injected, the change of the amplitude is linearly proportional to the logarithm of the concentration of HQ in the range 1.0×10 −2 –2.0×10 −4 M ( r =0.9965), whereas, when the concentration of HQ is over the range from 2.5×10 −4 to 4.0×10 −7 M, the calibration curve fits a second-order polynomial equation very well ( r =0.9983).

In order to elucidate the mechanism of Ce 4+ +BrO 3 − +H 2 SO 4 +fructose [F] oscillatory reaction which has no apparent bromine removal mechanism, detailed experimental studies have been undertaken to investigate (i) [Br − ] at different time intervals during oscillations, (ii) effect of addition of (a) Br − during oscillations, (b) fructose and BrO 3 − after stoppage of oscillations and (c) tartaric acid [TA], below the lower critical limit of [F] for oscillations. A reaction mechanism has been suggested which involves active participation of free radicals and which also correctly predicts most of the observed oscillatory features.

The experimental study of iodate-catalyzed disproportionation of aqueous hydrogen peroxide, called the Bray-Liebhafsky oscillating reaction (BLR), was performed by using membrane introduction mass spectrometry (MIMS). Thesequence of species O 2 , HIO 2 , HIO, and I 2 , which appear during the oscillation, was observed for the first time. The influence of ambient atmosphere, stirring rate, and temperature on the BLR was investigated. The contribution of gained results to the published models is discussed.