Catalysts Bray-Liebhafsky reaction

IV. Examinations of Catalysts Using the Bray-Liebhafsky Reaction... 

IV. EXAMINATIONS OF CATALYSTS USING THE BRAY-LIEBHAFSKY REACTION AS THE MATRIX SYSTEM... 

After reading previous sections, we can conclude that the Bray-Liebhafsky reaction system, as any oscillatory one, is extremely sensitive to various perturbations, and therefore suitable for analytical applications. They can be used as the matrix for analyzing properties of the substances that already exist in the system [17,18,42,56], but also the ones that only interact with it [10-17,19-22]. Beside others, such substances can be catalysts [93,94]. 

With aim to examine catalysts by the Bray-Liebhafsky reaction system as the matrix, two examples, one in the closed and the other in the open reactor, will be given in the following. 

With the aim to compare the activities of the two mentioned catalysts (HRP and apFe) we had to examine their kinetic properties. This is performed in the Bray-Liebhafsky reaction being in the oscillatory state. The reaction was conducted in the closed well-stirred reactor. 

In this series, the catalyst and hydrogen peroxide were mixed before adding to the solution of potassium iodate and sulfuric acid, where, in analogy with other investigations, the moment when two mentioned mixtures were connected was taken as the beginning of the Bray-Liebhafsky reaction. The period of their mutual reaction Q before adding to the solution of potassium iodate and sulfuric acid was different in different experiments. AU other parameters were kept... 

By the presence of either HRP or apFe, the Bray-Liebhafsky reaction is changed in a similar manner. Some amounts of the mentioned catalysts influence decrease, whereas the other amounts influence increase of the characteristic periods Ti and Tend - In other words, some amounts of mentioned catalysts cause the acceleration of the reactions (R), (O), and (D), whereas the other amounts cause their inhibition. Anyhow, by the presence of either HRP or apFe in the BL reaction, the new reaction system for hydrogen peroxide decomposition is formed. 

Three experimental series where temperature was the control parameter were performed under equal initial conditions. In the first series, the pure Bray-Liebhafsky reaction system was analyzed, whereas in the other two series the same system together with either catalyst A or catalyst B was considered. In the first series, the temperature was varied between 45.4 and 55.3°C, in the second series (BL system with catalyst A) between 48.2 and 58.1°C, and in the third series (BL system with catalyst B) between 45.9 and 60.0°C. 

FIGURE 8.15 The Bray-Liebhafsky reaction system without additional catalyst. (1) Time sequences with respect to temperature in °C (a) 49.5, (h) 49.9, (c) 50.2, (d) 50.7, (e) 51.0, (f) 55.3. (2) Bifurcation diagram with stable steady states (sohd circles) and envelop of large-amplitude oscillations (empty circles) and small amplitude oscillations (stars). (3) Square of oscillation amplitudes versus temperature [94]. 

Pejic, N., Cupic, Z., Anic, S., Vukojevic, V., and Kolar-Anic, Lj., The oscillatory Bray Liebhafsky reaction as a matrix for analyzing enzyme and polymeric catalysts for hydrogen peroxide, Sci. Sintering, 33, 107-115, 2001. 

The Bray-Liebhafsky system without an additional catalyst, the same system with peroxidase, and the same system with apFe are considered. The initial conditions for all experiments were identical. The initial amounts of catalysts were used in such a way to ensure equal concentrations of iron in the corresponding reaction system possessing one of the two examined catalysts [93]. The results are presented in Figure 8.8. 

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