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A kinetic method for the determination of l-tyrosine (Tyr) by analyte pulse perturbation, caused by different amounts of Tyr, in the Bray–Liebhafsky (BL) oscillatory reaction realized in a continuous-flow stirred tank reactor, is proposed. For such purposes, the BL oscillating reaction was kept in a stable non-equilibrium stationary state close to the bifurcation point and was used as the matrix reaction system. Under optimum reaction conditions, the linear relationship between the kinetic parameters, Δτ2 (the period between first two oscillations that appear after applied perturbation) as well as τend (the time elapsed between the perturbation of the BL reaction by Tyr and the termination of the oscillatory phase) and the Tyr concentrations is obtained over the ranges 1.1 × 10− 6 − 9.2 × 10− 6 mol L− 1 and 1.1 × 10− 6 − 1.4 × 10− 5 mol L− 1, with the limit of detections of 6.6 × 10− 7 mol L− 1 and 6.4 × 10− 7 mol L− 1. The described method that relies on a simple instrumental set-up, has been successfully applied to the determination of Tyr in a dietary supplement. Some aspects of the possible mechanism of Tyr action on the BL oscillator are discussed.

Dynamic states with intermittent oscillations consist of a chaotic mixture of large amplitude relaxation oscillations grouped in bursts, and between them, small-amplitude sinusoidal oscillations, or even the quiescent parts, known as gaps. In this study, intermittent dynamic states were generated in Bray–Liebhafsky (BL) oscillatory reaction in an isothermal continuously-fed, well-stirred tank reactor (CSTR) controled by changes of specific flow rate. The intermittent states were found between two regular periodic states and obtained for specific flow rate values from 0.020 to 0.082 min−1 . Phenomenological analysis based on the quantitative characteristics of intermittent oscillations, as well as, the largest Lyapunov exponents calculated from experimentally obtained time series, both indicated the same type of behavior. Namely, fully developed chaos arises when approaching to the vertical asymptote which is somewhere between two bifurcations. Hence, this study proposes described route to fully developed chaos in the Bray-Liebhafsky oscillatory reaction as an explanation for experimentally observed intermittent dynamics. This is in correlation with our previously obtained results where the most chaotic intermittent chaos was achieved between the periodic oscillatory dynamic state and stable steady state, generated in BL under CSTR conditions by varying temperature and inflow potassium iodate concentration. Moreover, it was shown that, besides the largest Lyapunov exponent, analysis of chaos in experimentally obtained intermittent states can be achieved by a simpler approach which involves using the quantitative characteristics of the BL reaction evolution, that is, the number and length of gaps and bursts obtained for the various values of specific flow rates.

The application of alternating current is advantageous in energy transfer over long distances. It is a well-known fact now, but subject of long conflict in the era of pioneering works in electric power production. There are also some processes in physical chemistry, organic and inorganic chemistry, in biochemistry and related sciences, which take place in opposite directions, with consecutive alternations in time. However, the very existence of alternate reactions, now known as the oscillatory or oscillating reactions, has long been disputed because it was thought that it is contrary to the basic principles of thermodynamics. Nevertheless, according to our knowledge, there are no oscillatory reactions without catalytic loop as the essential part of a mechanism. There could be a fundamental rule that catalysis is necessary to generate oscillations in concentrations and reaction rates. Particularly, homogeneous oscillatory reactions are often subject of research as relatively simple systems with good chance to clearly define feedbacks responsible for instability phenomena. However, oscillations can at least equally often be found in heterogeneous catalytic reactions. Recently, changes in product selectivity was proved when Pd catalyzed carbonylation of phenylacetylene was moved to the oscillatory dynamic state. With this simple result, the doors are now open for wide spectrum of research projects and applications.

In this paper, we intend to show the importance of the bifurcation analysis in understanding of an oscillatory process. Hence, we use the bifurcation diagram of the Bray-Liebhafsky reaction performed in continuous well-stirred tank reactor under controlled temperature variations for the determination of the activation energies as well as rate constants of particular steps appearing in the kinetic model of oscillatory reaction mechanism. This approach has led us to the development of general procedure for treatment of experimentally obtained data and extracting kinetic parameters from them, which was very important considering that some rate constants of the already proposed model could not be determined experimentally and have to be fitted (or guessed). Also, the proposed approach has the potential to inspire the refinement of already proposed models and the development of a new one that will be able to reproduce experimentally obtained system's dynamical features more successfully. In particular, the dynamic states of the Bray-Liebhafsky oscillatory reaction have been analyzed experimentally and numerically using already proposed model together with qualitative and quantitative analysis of bifurcation diagrams in both cases.

Two hydroxyanthraquinones, alizarin and purpurin, that have been used throughout history as a natural pigment, were extracted from roots of Rubia tinctorum from Serbia. As substances with important chemical activities and, therefore, with wide applications (for example in dyeing textile fabrics as well as in pharmacy because of their anti-inflammatory, anti-cancer, antiviral, antimicrobial and antioxidant activities, etc.) they were analyzed in the kinetically very sensitive Bray–Liebhafsky (BL) oscillatory reaction. However, although they are both, hydroxyanthraquinones it is shown that their interactions with BL nonlinear reaction system differ significantly. Consequently, two different reactions were used to explain the mechanism of their chemical activities. The numerical simulations based on a standard model of the BL oscillatory reaction together with proposed reactions due to alizarin/purpurin interactions with a matrix are correlated with experimental investigations. Moreover, it is shown that very small amounts of alizarin and purpurin (from about 1 × 10–7 M) produce the response of the BL matrix such that micro-quantitative analysis based on the BL oscillatory reaction can be successfully performed in this reaction system. The linear response of the BL matrix on the presence of alizarin and purpurin (necessary for microquantitative determination) is analyzed as a function of two concentration sensitive parameters: pre-oscillatory period τ1 and potential shift after perturbation ΔE.

The use of solid particles as a catalyst in a certain reaction system results in emergence of heterogeneous catalysis. More active catalyst is obtained by resizing the particles up to nanodimension. Nanocatalysts are the most active catalysts considering minimal size which gives maximal activity. Main drawbacks of nanocatalysis will be presented in this chapter through synthesis, characterization, and activity-selectivity relations. Special attention is given to catalysts for application in environmental protection and photocatalytic hydrogen production.

Intermittent oscillations as a chaotic mixture of large amplitude relaxation oscillations, grouped in bursts and small-amplitude sinusoidal ones or even quiescent parts between them known as gaps, were found and examined in the Bray-Liebhafsky (BL) reaction performed in CSTR under controlled temperature variations. They were obtained in a narrow temperature range from 61.0 degrees C to 63.1 degrees C, where 61.0 degrees C is the critical temperature for burst emergence from the stable steady state and 63.1 degrees C is the critical temperature for gap emergence from regular oscillations. Since intermittencies appear gradually from the regular oscillatory state, and no hysteresis was obtained with decreasing/increasing temperature in the vicinity of these two bifurcations, a linear relationship between (tau(B)/tau)(2) and (tau(G)/tau)(2) (where tau(B), tau(G) and tau denotes duration of bursts, gaps, and whole experiment, respectively), as a function of the temperature as the control parameter, was expected and obtained. Although these intermittent oscillations are chaotic with respect to the lengths of individual gaps as well as bursts, their deterministic behavior related to temperature was additionally established. Thus, the number of bursts or gaps per unit of time (N-B/tau and N-G/tau) has the form of a normal distribution function over the temperature range in the region where intermittencies are obtained. Temperature dependence of the Lyapunov exponents was also described by a function of the normal distribution form. Hence, we established some regularities in the chaotic behavior of intermittent oscillations that are common in life but difficult for determinations.

A brief review of Professor Ljiljana Kolar-AniAc's research on the dynamics and kinetics of complex reaction systems is given, with a special emphasis on contributions in the research of the oscillatory processes of Bray, Belousov and Hypothalamic-pituitary-adrenal system.

The system KSCN-H2O2-CuSO4-NaOH, also known as the OrbA n-Epstein oscillatory reaction, is exposed to external perturbations by several phenolic compounds: catechol, resorcinol, hydroquinone, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, caffeic acid, and ferulic acid. As a result of the performed perturbation in most examined cases, oscillations have been inhibited for some characteristic time, and resumed afterwards. The evaluated inhibition time is typical for each substance and strongly dependent on its concentration. The chemical mechanism of the interaction between the OrbA n-Epstein system and phenolic compounds is briefly discussed. Numerical simulations are performed using the original OrbA n-Epstein model with 30 reactions, extended by three reactions describing the interaction with inhibitory substances. The rate constants of three added reactions are adjusted to fit experimental inhibition times, and compared among used compounds. The observed effects are discussed further in relation with the bond dissociation enthalpy theory. Unlike other tested compounds, 2,5-dihydroxybenzoic acid remains off from predicted order of activity.

Diatomite supported NiMgAg catalysts, NiMgAg/D, were prepared by the precipitation-deposition method followed by drying, reduction and passivation. The preparation of the catalysts was performed with different loading of silver ranging from 0.16 to 5.88 wt% and constant molar ratios of SiO2/Ni and Mg/Ni equal to 1.07 and 0.1, respectively. The characterization of the catalysts was performed with N-2-physisorption, mercury intrusion porosimetry, H-2-chemisorption, X-ray diffraction, temperature programmed reduction, and scanning electron microscopy-energy dispersive X-ray analysis. The partial hydrogenation of soybean oil from initial to final iodine value of 90 was carried out at 160 A degrees C and H-2 pressure of 0.16 MPa using stirred semi-batch reactor. Soybean oil was hydrogenated over NiMgAg/D catalysts and NiMg/D catalyst (without silver addition) that was prepared using the same procedure as used for catalysts modified with silver. The selectivity towards trans fatty acid and saturated fatty acid formation was determined for both types of catalysts. By comparing the selectivity of the NiMgAg/D catalysts with the NiMg/D catalyst the promoting effect of silver modifier on the catalyst behavior in the hydrogenation of soybean oil was observed, and correlated with changing of the catalyst surface characteristics caused by the different Ag loading. It was found that the addition of silver to NiMg/D catalyst decreased both the selectivity towards trans fatty acids formation and the selectivity towards saturated fatty acids. For the same iodine value decay, the catalyst with the highest Ag loading (5.88 wt%) had the lowest level of both trans fatty acids and saturated fatty acids in the hydrogenation of soybean oil under studied operating conditions. The hydrogenation activity of NiMgAg/D catalysts is lower than NiMg/D catalyst and decreases with increasing Ag loading. The correlation between adsorption characteristics of the catalysts and their hydrogenation activities was established. The proposed simplified kinetic model to describe the kinetics of soybean oil hydrogenation gave a good description of the experimental data.

The intermittency or intermittent bursting as the type of dynamic state when two qualitatively different behaviors replace one another randomly during the course of the reaction, although all the control parameters remain constant, is found in the BriggsRauscher oscillating system moderated by a very small amount of phenol. Within a range of phenol concentrations, the oscillation amplitude is diminished considerably, and after oscillations cease, they repeat intermittently, giving several bursts of oscillations. For the concentrations used here, the range of phenol concentrations where intermittent bursting oscillations occur in a closed reactor is ca. 1.8 � 10 � 5 to 3.6 � 10 � 5 m. Bursting also occurs in an open reactor and can be sustained indefinitely at 5.53 � 10 � 5 m concentration. The intermittent bursting behavior is robust, and can be achieved at a variety of conditions.

This paper investigates multicomponent gas adsorption at the active surface of plasmonic chemical sensors and shows that there are situations where transients in a single sensor element can be used for simultaneous detection of different gases in multicomponent mixtures. A general master equation set is provided, describing multicomponent adsorption. Analytical expressions for sorption rates are derived and high-accuracy simplified models are proposed. Expressions for adsorption rate constants and rates and for number of binding sites are proposed. The derived analytical model takes into account the adsorbate molecule size, distribution of binding sites as determined by the crystallographic structure of the sensor surface and multi-site adsorption. The model allows for the calculation and optimization of deterministic behavior of the system. It is shown that trace amounts of target gas species can be made detectable by adding controlled amounts of known carrier gas. Besides being applicable in plasmonic sensor design and optimization, the obtained results may be of importance in situations where fast and low-cost detection of trace amounts of gases is needed, including natural gas leakage in residential heating, radon outgassing in dwellings, environmental protection, homeland defense and hazardous materials management, greenhouse footprint investigations, etc. This is the peer-reviewed version of the article: Jaksic, O.M., Randjelovic, D., Jaksic, Z.S., Cupic, Z.D., Kolar-Anic, L.Z., Plasmonic Sensors in Multi-Analyte environment: rate constants and transient analysis, Chemical Engineering Research and Design (2013), [http://dx.doi.org/10.1016/j.cherd.2013.06.033] [http://cer.ihtm.bg.ac.rs/handle/123456789/1543]

The electrochemical oxidation of methanol has been carefully studied due to its application in fuel cells. In this work electrooxidation of methanol was investigated on bare platinum electrode, the platinum electrode covered with Nafion and platinum supported on zeolite 13X. Along with classical electrochemical methods, attractor reconstruction was used to make rough distinction among possible reaction mechanisms on different forms of Pt. The obtained transient voltammogram records were used to calculate apparent rate constants for methanol oxidation limiting steps in transient period. All samples contributed to methanol oxidation by basically same reaction mechanism, but with significantly different apparent rate constants.

The analysis of adsorption kinetics is given, assuming no dissociative adsorption takes place and no multiple binding sites exist. The phenomenological nonlinear model and the simple linear model are considered from the point of view of surface plasmon resonance (SPR) chemical sensors. A simple method for analytical calculation of the necessary rate constants is proposed. A comparative analysis of the described models is performed. Two conditions that affect the validity of the linear model are found. First one, referring to the ratio between the overall number of particles and the number of binding sites, and the second one, that guarantees the validity of linear model in much broader spectrum of practical situations, referring to the ratio of rate constants. A method for avoiding the accumulation of numerical errors in calculus is also proposed. The presented approach is general and can be used in various applications, including other types of chemical sensors, membranes for filtering, different catalytic systems, resonant micro or nano-electro-mechanical structures.

Chaotic dynamic states with intermittent oscillations were generated in a Bray-Liebhafsky (BL) oscillatory reaction in an isothermal open reactor i.e., in the continuously-fed well-stirred tank reactor (CSTR) when the inflow concentration of potassium iodate was the control parameter. They are found between periodic oscillations obtained when [KIO3](0) LT 3.00 x 10(-2) M and stable steady states when [KIO3](0) > 4.10 x 10(-2) M. It was shown that the most chaotic states obtained experimentally somewhere in the middle of this region are in high correlation with results obtained by means of largest Lyapunov exponents and phenomenological analysis based on the quantitative characteristics of intermittent oscillations.

Stoichiometric network analysis (SNA) represents a powerful mathematical tool for stability analysis of complex stoichiometric networks. Recently, the important improvement of the method has been made, according to which instability relations can be entirely expressed via reaction rates, instead of thus far used, in general case undefined, current rates. Such an improved SNA methodology was applied to the determination of exact instability conditions of the extended model of the hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrinological system, whose hormone concentrations exert complex oscillatory evolution. For emergence of oscillations, the Hopf bifurcation condition was utilized. Instability relations predicted by SNA showed good correlation with numerical simulation data of the HPA axis model.

Stoichiometric Network Analysis (SNA) is a powerful method that can be used to examine instabilities in modelling a broad range of reaction systems without knowing the explicit values of reaction rate constants. Due to a lack of understanding, SNA is rarely used and its full potential is not yet fulfilled. Using the oscillatory carbonylation of a polymeric substrate [poly(ethylene glycol) methyl ether acetylene] as a case study, in this work, we consider two mathematical methods for the application of SNA to the reaction models when conservation constraints between species have an important role. The first method takes conservation constraints into account and uses only independent intermediate species, while the second method applies to the full set of intermediate species, without the separation of independent and dependent variables. Both methods are used for examination of steady state stability by means of a characteristic polynomial and related Jacobian matrix. It was shown that both methods give the same results. Therefore, as the second method is simpler, we suggest it as a more straightforward method for the applications. Published by AIP Publishing.

Al,Fe-pillared clay was synthesized from domestic clay from Bogovina according to a common procedure: grinding, sieving, Na exchange, pillaring, drying and calcination. Two synthesized samples differing only in calcining conditions were prepared. Phase composition and textural properties of the starting clay and synthesized pillared clays were characterized using X-ray diffraction and physisorption of nitrogen. Catalytic tests were performed using sample with better textural properties being the one submitted to milder calcining conditions. Catalytic wet peroxide oxidative degradation of aromatic compounds phenol and tartrazine on the synthesized catalyst was confirmed showing better efficiency in the case of tartrazine.

The kinetic investigations of the malonic acid decomposition (8.00 x 10(-3) mol dm(-3) a parts per thousand currency sign [CH(2)(COOH)(2)](0) a parts per thousand currency sign 4.30 x 10(-2) mol dm(-3)) in the Belousov-Zhabotinsky (BZ) system in the presence of bromate, bromide, sulfuric acid and cerium sulfate, were performed in the isothermal closed well stirred reactor at different temperatures (25.0A degrees C a parts per thousand currency sign T a parts per thousand currency sign 45.0A degrees C). The formal kinetics of the overall BZ reaction, and particularly kinetics in characteristic periods of BZ reaction, based on the analyses of the bromide oscillograms, was accomplished. The evolution as well as the rate constants and the apparent activation energies of the reactions, which exist in the preoscillatory and oscillatory periods, are also successfully calculated by numerical simulations. Simulations are based on the model including the Br(2)O species.

Identification of trends and their correspondence with dynamical state transitions are briefly discussed on several reaction network models. The influence of different threshold values on the trend analysis and dynamical state analysis results is examined. Both methods are applied here to the results of the numerical simulation. For this purpose the models of three reaction systems are used: simple model of consecutive, first order, equilibrium reactions, partial oxidation of cyclohexane, and model of the oscillatory reaction Bray Liebhafsky. Detailed kinetic analysis confirmed that transient dynamical states may be identified through the symbolic representation of the sequence of trend episodes in experimentally obtainable time series. Stoichiometric Network Analysis of possible dynamical states was used to identify reaction pathways responsible for the sequences of trend episodes. Some technical problems were also addressed, connected with selection of the threshold value and dynamical state notion.

In this paper, an already published model of the Bray-Liebhafsky reaction was improved by removing the direct autoinhibitory step, which resulted in a new variant of the model with more realistic kinetic scheme than the earlier version. The obtained variant of the model retains all intermediate species (I-, HIO, HIO2 and I-2) that were present in the previous model and has one reaction less. Stability analysis of the improved model was performed by stoichiometric network analysis (SNA). By this method, it was shown that improved model can simulate Andronov-Hopf and saddle-node bifurcations. In order to confirm the results of SNA, bifurcation analysis was performed with the initial concentrations of [H2O2](0) as the control parameter. With selected set of rate constants and constant concentrations of external species, two Andronov-Hopf bifurcations were detected at [H2O2](0) = 5.62 x 10(-2) M and [H2O2](0) = 10.73 M, while the rate constants ought to be changed for a saddle-node to occur. Bifurcation analysis also showed that the interaction between intermediate species I-, HIO and HIO2 has a crucial impact on the emergence of Andronov-Hopf bifurcation.

The mixing of different types of bifurcations, i.e. supercritical Andronov–Hopf (SAH), double loop (DL) and saddle-loop (SL) bifurcations in the vicinity of their total annihilation, is examined on the highly nonlinear six-variable model for the Bray–Liebhafsky (BL) oscillatory reaction under continuously well-stirred tank reactor (CSTR) conditions. For this kind of the reaction system where the law of mass conservation is additional constraint that must be satisfied and where because of that, some simple bifurcations cannot be formed independently to the others, the considered transformations of the bifurcations are particularly important. That is why as the control parameters for bifurcation analysis, the specific flow rate (j0), as well as the inflow hydrogen peroxide concentration (h = [H2O2]in), were used. The complex bifurcations obtained from numerical simulations are compared with some experimental results. It was shown that these complex bifurcations cannot be easily recognized in experimental investigations without knowing their evolution.

By numerically simulated Bray-Liebhafsky (BL) reaction under a continuously fed well stirred tank reactor (CSTR) conditions, we discussed the attractors and Poincar, 1D maps with respect to flow rate as the control parameter. The new technique of the return maps from transient trajectories over the slow manifold is developed and applied in order to explore its multilayered structure related to dynamical states (periodic and aperiodic -chaotic oscillating modes) of the system. Kinetic relations underlying the slow manifold structure are briefly discussed.

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO2/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger-Akahira-Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (E-a) is practically constant in the conversion range of 0.20 LT = alpha LT = 0.80. In the considered conversion range, following values of E-a were found: 134.5 kJ mol(-1) (SiO2/Ni = 0.20), 139.6 kJ mol(-1) (SiO2 /Ni = 0.80), and 128.3 kJ mol(-1) (SiO2/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO2/Ni molar ratios is a complex process and can be described by the Sestak-Berggren autocatalytic model. It was found that the reaction is more Langmuir-Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni-O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases. This is the peer reviewed version of the following article: Janković, B., Čupić, Ž., Jovanović, D., Stanković, M., 2016. Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere. Chemical Engineering Communications 203, 182–199. [https://doi.org/10.1080/00986445.2014.983268] [http://cer.ihtm.bg.ac.rs/handle/123456789/1980]

Soybean oil has been partially hydrogenated in the presence of a synthesized nickel catalyst, in an industrial reactor, under the standard industrial working conditions. The GC measurements of fatty acids in the investigated oil and hydrogenated products have been performed. The total trans isomers content has been determined by the IR spectroscopy. The model is established, which could be useful for the characterization of hydrogenation and isomerization reactions of poly-unsaturated acids. Iteration procedure, incorporating numerical simulation in each step is used to calculate rate constants of the proposed model from the comparison of the experimental and calculated kinetic runs. By the simultaneous treatment of the kinetic runs for the fatty acids composition and trans -isomer content, the 12 rate constants of individual hydrogenation and isomerization reaction steps are obtained.

Perturbation of the BrayLiebhafsky non-oscillating subsystem (mixture of KIO3 and H2SO4), i.e., Dushman reaction (DR), by piroxicam (PX), was observed in an open reactor, i.e., in the continuously fed well-stirred tank reactor (CSTR). Monitoring the response of DR to perturbations by different concentrations of PX allows developing a simple procedure for quantitative determination of this analyte in both bulk drug and pharmaceutical preparation (injection). A tentative perturbation mechanism of PX action on the DR matrix, based on a kinetic scheme that was suggested by Agreda et al., is proposed. The PX reactivity in DR has been generally related to the reaction of PX with hypoiodous acid (HIO) present in the matrix.

By numerical calculations based on our previously proposed model with Br2O intermediate species we were able to simulate complex evolution of the Belousov-Zhabotinsky (BZ) reaction under batch conditions. In the defined region of initial malonic acid concentration [MA](0) (1.00 x 10(-3) mol dm(3) a parts per thousand currency sign [MA](0) a parts per thousand currency sign 1.50 mol dm(-3)) different sequences of regular and complex periodic and aperiodic oscillations were obtained. It is noticed that the bromine evaporation significantly affects the dynamics of the reaction.

The time series obtained by numerical simulations of the model of the Bray-Liebhafsky oscillatory reaction is analyzed under the continuously fed well stirred tank reactor (CSTR) conditions, with the aim to find bifurcation points in which system of Bray-Liebhafsky oscillatory reaction transforms from stable to unsta- ble state and vice versa. Types of bifurcation points, supercrit- ical and subcritical Andronov-Hopf bifurcation and saddle-loop bifurcation are determined from characteristic scaling laws.

Behavior of the Bray-Liebhafsky oscillatory reaction in the presence of acid-base polymers with and without ferric ions is analyzed. The influence of hydrogen ions on the overall reaction is shown.

The non-periodic, periodic and chaotic regimes in the Bray-Liebhafsky (BL) oscillatory reaction observed in a continuously fed well stirred tank reactor (CSTR) under isothermal conditions at various inflow concentrations of the sulfuric acid were experimentally studied. In each series (at any fixed temperature), termination of oscillatory behavior via saddle loop infinite period bifurcation (SNIPER) as well as some kind of the Andronov-Hopf bifurcation is presented. In addition, it was found that an increase of temperature, in different series of experiments resulted in the shift of bifurcation point towards higher values of sulfuric acid concentration.

By numerically simulating the Bray-Liebhafsky (BL) reaction (the hydrogen peroxide decomposition in the presence of hydrogen and iodate ions) in a continuously fed well stirred tank reactor (CSTR), we find "structured" types of chaos emerging in regular order with respect to flow rate as the control parameter. These chaotic "structures" appear between each two successive periodic states, and have forms and evolution resembling to the neighboring periodic dynamics. More precisely, in the transition from period-doubling route to chaos to the arising periodic mixture of different mixed-mode oscillations, we are able to recognize and qualitatively and quantitatively distinguish the sequence of "period-doubling" chaos and chaos consisted of mixed-mode oscillations (the "mixed-mode structured" chaos), both appearing in regular order between succeeding periodic states. Additionally, between these types of chaos, the chaos without such recognizable "structures" ("unstructured" chaos) is also distinguished. Furthermore, all transitions between two successive periodic states are realized through bifurcation of chaotic states. This scenario is a universal feature throughout the whole mixed-mode region, as well as throughout other mixed-mode regions obtained under different initial conditions.

In the already proposed model of the Belousov-Zhabotinsky reaction with the Br(2)O species as intermediate one, the reactions with malonyl (MA(center dot)), bromomalonyl (BrMA(center dot)) and tartronyl (TA(center dot)) radicals were introduced with aim to explore their role in overall dynamics. The related numerical simulations of the experimentally obtained dynamic states under batch conditions were successfully performed.

Polymer supported catalysts with Co(II) and Cr(VI) ions were prepared and characterized by means of FTIR, diffuse reflectance UV-vis, nitrogen physisorption, mercury porosimetry and SEM-EDX measurements. The catalytic activity and selectivity of the polymer supported catalysts were tested in aerobic liquid-phase partial oxidation of cyclohexane in a polytetrafluoroethylene lined reactor. The influence of reaction time and temperature, main products addition, mass of the catalyst and different metals loading was investigated. Product yield and cyclohexyl hydroperoxide formation in the catalytic system were used as critical parameters which could be optimized by changing the cobalt content on the polymer and the catalyst mass used in the catalytic runs. By increasing cobalt content, a higher activity and corresponding lower selectivity towards cyclohexanone were obtained. This study indicates that the selectivity towards cyclohexanone and cyclohexanol is mainly defined by the yield and type of the catalyst with minor influence of temperature and main products addition. In addition catalysts were used for deperoxidation of cyclohexyl hydroperoxide in mild conditions. Nearly the same selectivity towards cyclohexanone and cyclohexanol is achieved using the cobalt containing catalyst, while a higher selectivity towards cyclohexanone is achieved using the chromium containing catalysts. (C) 2009 Elsevier B. V. All rights reserved.

We applied multifractal analysis on time series obtained by deterministic simulation of the Bray-Liebhafsky oscillatory reaction. Large deviation spectrum was used to represent multifractal properties of the attractor. We obtained spectrums with two peaks, one in region of low and the other in region of high values of Holder exponent. Their intensity depends on flow rate. The method developed on the results from numerical simulations is tested on the experimental record from the same reaction system and multifractality of the time series is confirmed.

The infuence of poly-4-vinylpyridine-co-divinylbenzene-Co2+ catalyst on the Bray-Liebhafsky (BL) oscillator used as the matrix for establishing catalyst's activity was analyzed. The addition of the catalyst do not change the dynamics of the reaction in the BL matrix, but the periods of the oscillatory evolution as well as the preoscillatory period (tau(1)) and the duration from the beginning of the reaction to the end of the oscillatory state (tau(end)). All experimental results are simulated satisfactory.

The influence of the initial malonic acid concentration [MA](0) (8.00 x 10(-3) LT = [MA](0) LT = 4.30 x 10(-2) mol dm(-3)) in the presence of bromate (6.20 x 10(-2) mol dm(-3)), bromide (1.50 x 10(-5) mol dm(-3)), sulfuric acid (1.00 mol dm(-3)) and cerium sulfate (2.50 x 10(-3) mol dm(-3)) on the dynamics and the kinetics of the Belousov-Zhabotinsky (BZ) reactions was examined under batch conditions at 30.0 degrees C. The kinetics of the BZ reaction was analyzed by the earlier proposed method convenient for the examinations of the oscillatory reactions. In the defined region of parameters where oscillograms with only large-amplitude relaxation oscillations appeared, the pseudo-first order of the overall malonic acid decomposition with a corresponding rate constant of 2.14 x 10(-2) min(-1) was established. The numerical results on the dynamics and kinetics of the BZ reaction, carried out by the known skeleton model including the Br2O species, were in good agreement with the experimental ones. The already found saddle node infinite period (SNIPER) bifurcation point in transition from a stable quasi-steady state to periodic orbits and vice versa is confirmed by both experimental and numerical investigations of the system under consideration. Namely, the large-amplitude relaxation oscillations with increasing periods between oscillations in approaching the bifurcation points at the beginning and the end of the oscillatory domain, together with excitability of the stable quasi-steady states in their vicinity are obtained.

Polymer-supported Co(II) catalyst was prepared and its activity and selectivity in the partial oxidation of cyclohexane was determined at several temperatures in a polytetrafluoroethylene reactor ( PTFE). The catalyst was characterized by means of SEM-EDX, FTIR, diffuse reflectance UV-Vis, N-2 sorption, and mercury porosimetry. Activation energies were determined under steady state conditions for the net production of cyclohexanone and cyclohexanol and for cyclohexane and oxygen net consumption. Some activation energies were lower than the ones reported for the uncatalyzed process, indicating that the catalyst played an important role in the initiation of the free-radical reaction.

Macroporous cross-linked copolymer of 4-vinylpyridine and 25% (4:1) divinylbenzene is analyzed under open conditions, that is in a continuous well-stirred tank reactor (CSTR). With this aim the appropriate bifurcation diagram is found and the behavior of the system with and without polymer in the vicinity of the bifurcation point is used for the polymer examinations. Two different granulations of polymer are considered. Moreover, some physicochemical characteristics of the polymer, such as specific surface area, skeletal and particle density, are determined.

Contraction procedure of the complex chemical models with several independent intermediates by the stoichiometric network analysis, as the very useful method for such purposes, is demonstrated on the model for the hydrogen peroxide decomposition in the presence of iodate and hydrogen ions. It is shown that after reduction the model preserve main characteristics of the initial one.

The catalytic wet peroxide oxidation (CWPO) of toluene on two bentonite-based AlFe-pillared clays (PILCs) with different iron contents was investigated. The PILCs were obtained using bentonite clay from Bogovina, Serbia. The change in chemical and phase composition and textural properties of the starting clay and synthesized catalysts was monitored using X-ray diffraction, inductively coupled plasma optical emission spectrometry, UV-Vis diffuse reflectance spectrometry, and physisorption of nitrogen. The catalytic performance was examined using gas chromatography. The Na-exchange process lowered the (001) smectite basal plane spacing, but the clay retained its swelling properties, while the pillaring process increased it. The surface areas of both synthesized pillared clays increased to similar values although their Fe content was different. At 37 degrees C, both catalysts show significant toluene degradation, with the one richer in Fe having higher efficiency. The leaching of the active cations during reaction was negligible, and the catalysts were stable. AlFe-pillared clay catalysts can be used in CWPO for the elimination of BTEX compounds from plant effluent streams.