Activity of Polymer Supported Cobalt Catalyst in the Bray-Liebhafsky Oscillator

Transcription

1 University of Belgrade From the SelectedWorks of Zeljko D Cupic 29 Activity of Polymer Supported Cobalt Catalyst in the Bray-Liebhafsky Oscillator Zeljko D Cupic, Institute of Chemistry, Technology Metallurgy Available at:

2 ISSN , Russian Journal of Physical Chemistry A, 29, Vol. 83, No. 9, pp Pleiades Publishing, Ltd., 29. CHEMICAL KINETICS AND CATALYSIS Activity of Polymer Supported Cobalt Catalyst in the BrayLiebhafsky Oscillator* S. Anic a, J. Maksimovi a, D. Lon arevi b, N. Peji c,. D. upi b ' c ' c c ' c ' Z C c ' a Faculty of Physical Chemistry, University of Belgrade, Studentski trg 26, P.O. Box 37, YU Belgrade, Serbia b IChTM, Center of Catalysis Chemical Engineering, Njegoševa 2, Belgrade, Serbia c Faculty of Pharmacy, University of Belgrade, Belgrade, Serbia boban@ffh.bg.ac.yu Abstract The infuence of poly-4-vinylpyridine-co-divinylbenzene-co 2+ catalyst on the BrayLiebhafsky (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 (τ ) the duration from the beginning of the reaction to the end of the oscillatory state (τ end ). All experimental results are simulated satisfactory. DOI:.34/S X INTRODUCTION The oscillatory processes have been successfully applied for the analytical purposes [7]. Some of them were used for the characterization of catalysts [823]. Namely, the properties of the catalyst based on polymer functionalized by iron [82] enzyme peroxidaze [2, 23] was tested by the Bray Liebhafsky oscillator as the matrix. The subject of this paper is the polymer supported cobalt catalyst examined by a perturbation of the BL matrix. The BrayLiebhafsky oscillatory reaction is the decomposition of hydrogen peroxide into the water oxygen in the presence of iodate hydrogen ions [24, 25]: H +, IO 3 2H 2 O 2 2H 2 O + O 2. (D) k D In this reaction numerous intermediates as I, I 2, HOI, HOOI, etc., exist [2428]. The reaction (D) is the result of the oxidation (O) of iodine to iodate k O I 2 + 5H 2 O 2 2IO 3 + 2H + + 4H 2 O, the reduction (R) of iodate to iodine 2IO 3 2H + k + + 5H 2 O R 2 I 2 + 5O 2 + 6H 2 O. (O) (R) The decomposition of hydrogen peroxide (D) in the BL matrix can be described by equation τ end = ---- ln[ H 2 O 2 ] end ln[ H 2 O 2 ], k D () where [H 2 O 2 ] is initial concentration [H 2 O 2 ] end the concentration at the end of oscillogram [29]. In *The article is published in the original. k D the particular system consisting of hydrogen peroxide, potassium iodate sulfuric acid, the rate constant k D is a function of potassium iodate sulfuric acid k D = k[ KIO 3 ] [ H 2 SO 4 ] q. (2) Influence of sulfuric acide on the reaction (D) is complex, between first second order ( < q < 2) depending on the range of values of [H 2 SO 4 ]. It was also found that there is the relations between the rate constants of the reactions (D), (R), (O), the periods τ τ end, also the total number of oscillations (n) [23, 3, 3]. Therefore, the mentioned periods can be used in kinetics analysis instead the rate constants. EXPERIMENTAL Catalyst was prepared by wetness impregnation of cobalt(ii)-nitrate on the macroreticular copolymer of poly-4-vinylpyridine with divinylbenzene. The cobalt content on polymer was 5.72 wt % [32]. All experiments were conducted in the closed wellstirred reactor. Volume of the reaction mixture was 52 ml. The reaction between 25 ml of sulphuric acid, 25 ml of potassium iodate 2 ml of hydrogen peroxide was examinated in the reaction vessel (METH- ROM EA 876-2) protected from light. The I ion sensitive electrode (Metrohm ) as the working electrodes, reference Ag/AgCl electrode (Metrohm ) were used. In the reference Ag/AgCl electrode, the inner electrolyte was a 3 mol l KCl the outer electrolyte was a saturated solution of K 2 SO 4. The potential changes of I electrodes during the experiment were followed written down using data collector (EH4 ph meter 468

3 ACTIVITY OF POLYMER SUPPORTED COBALT CATALYST 469 E, mv (a) (b) τ, min Fig.. The experimental (a) calculated (b) oscillograms of the matrix perturbed matrix by cobalt catalyst; () BL, (24) BL +.3,.5,.7 g catalyst, respectively. Measuring instruments Miljkovic Budimir others O.D.) connected with PC computer. Thermometer condenser were immersed into the reaction vessel. During the experiments, the temperature of reaction vessel was regulated by a thermostat (Julabo ED, Germany) with precision ±. K. The reaction mixture was stirred by a magnetic stirrer (IKA-COM- BIMAG RET) at 9 rpm. All substances were produced by Merck (Darmstadt, Germany). The solutions were prepared by p.a. chemicals with deionization water with specific resistance 8 MΩ/cm. In all experiments, next parameters were kept constant: [KIO 3 ] = mol/dm 3, [H 2 SO 4 ] = mol/dm 3, [H 2 O 2 ] = mol/dm 3, stirrer speed equal 9 rpm T = 62 C. The measurements were done in two independent series: in homogenous BL matrix, in the heterogeneous mixture of BL matrix the catalyst. The substances were added in the reaction vessel by the following order: catalyst, KIO 3, H 2 SO 4 finally H 2 O 2 was added when the temperature the potential were stardized. For the beginning of the reaction, the moment when of hydrogen peroxide was added to the vessel, was taken. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 9 29

4 47 ln(ln(τ end /τ* end )) (a) (b) ANI C ' et al. the same type are obtained, indicating that the dynamics of the observed processes is not changed. Moreover, the number of oscillations (n) the duration of the oscillograms (τ end ) decrease, whereas the preoscillatory period (τ ) increases, when amount of catalyst increases (Fig. ). In the presence of the catalyst in the matrix we must involve new rate constant for the overall process (D). Similar as in the [33] we can suppose that the catalyst influences on k D by the relation k* = k D ( exp( x( m cat * ) y )), (3) lnm* kat Fig. 2. Experimental (a) calculated (b) dependence of τ end / τ end * on m kat *. RESULTS AND DISCUSSION The iodide oscillograms of the BL matrix the matrix with various amounts of polymer supported cobalt catalyst are presented in Fig.. Oscillograms of where m kat * is dimensionless mass of the catalyst normalized with respect to mass units, x y are empirical kinetic parameters. Since the dynamics of the BL reaction does not change in the presence of catalyst, the equation () can be applied on perturbed BL system. In this case according to equations () (3) we obtained following relation: ln[ ln( τ end /τ end * )] = lnx + ylnm cat *. (4) Where τ end * is length of oscillograms of perturbed BL system. The validity of equation (4) is illustrated in Fig. 2. From linear dependence of ln(ln(τ end / * )) on τ end Rate constants activation energies (in kj/mol) used in numerical simulations of the BrayLiebhafsky reaction its perturbation [3438] Rate Rate constant at 62 C E a [I k ][ ][H + ] 2 = k [I IO 3 ] k = M 3 min 3.4 k [HIO][HIO 2 ] = k [HIO][HIO 2 ] k = M min 5. k [HIO 2 ][I ][H + ] = k 2 [HIO 2 ][I 2 ] k = 5.59 M 2 min k 3 [I 2 O] = k 3 [I 2 O] k = min k [HIO] 2 = k 3 [HIO] 2 3 k = M min 3 4. k [HIO][I ] = k 4 [HIO][I 4 ] k = 3.7 M min 4.5 k [I 2 ]/[H + 4 ] = k 4 [I 2 ] k = 5.22 Mmin ( k + [H + 5 ' k 5 '' ])[HIO][H 2 O 2 ] = k 5 [HIO][H 2 O 2 ] k = M min 5 ' 34. k = M 2 min 5 '' 34. k 6 [I 2 O][H 2 O 2 ] = k 6 [I 2 O][H 2 O 2 ] k = M min ( + [H + k 8 ' k 8 '' ])[ IO 3 ][H 2 O 2 ] = k 8 [H 2 O 2 ] k = M min 8 ' 5. k = M 2 min 8 '' 98. k [Co 2+ ][H 2 O 2 ][H + ] = k 9 [Co 2+ 9 ][H 2 O 2 ] k =.37 2 M 2 min k [HO ][H 2 O 2 ] = k [HO ][H 2 O 2 ] k = 6.5 M min.33 [Co 3+ ] ] = k 9 [Co 3+ k HO 2 ][ HO 2 ] k = M min.3 Note: k i is the rate constant of reaction R i. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 9 29

5 ACTIVITY OF POLYMER SUPPORTED COBALT CATALYST 47 ln( m cat * ), we evaluate the parameters x y, which amounts, x = 2. y =.2. NUMERICAL SIMULATIONS The numerical simulations of the BrayLiebhafsky reaction were carried out using the MATLAB program package under the conditions used in the experiments. In our simulations, a set of reactions (R)(R6), (R8), suggested in [3437] IO 3 + I + 2H + HIO + HIO 2, (R) HIO 2 + I + H + I 2 O + H 2 O, (R2) I 2 O + H 2 O 2HIO, (R3) HIO + I + H + I 2 + H 2 O, (R4) HIO + H 2 O 2 I + H + + O 2 + H 2 O, (R5) I 2 O + H 2 O 2 HIO + HIO 2, (R6) IO 3 HIO 2 + H 2 O 2 + H + + H 2 O, (R7) IO 3 + H + + H 2 O 2 HIO 2 + O 2 H 2 O (R8) must be complete by three new reactions for the interaction of the BL matrix with polymer supported cobalt catalyst: Co 2+ + H 2 O 2 + H + Co 3+ + HO + H 2 O, (R9) HO + H 2 O 2 HO 2 + H 2 O, (R) Co 3+ + Co 2+ + H + + O 2. (R) Almost all rate constants (table) were taken from earlier numerical simulations [3, 35]. The rate constant for reaction (R3) was changed slightly to obtain better agreement with the experimental results. The rate constant for reaction (R) was found in the literature [38], while the rate constants for reactions (R9) (R) were obtained in this work. Figure b shows the simulation results of the Bray Liebhafsky reaction without with various amounts of polymer supported cobalt catalyst. In view of imperfect model, we have not obtained same value for the duration of the oscillograms, but there is a good trend (Fig. 2b). We have received a good agreement of the parameters x y (x = 4.44, y =.4) with experimental ones (x = 2. y =.2). HO 2 CONCLUSION Presence of the catalyst under applied conditions did not change the dynamics of the BL reaction. By the formal kinetic analysis we did evaluate the activity of the tested catalyst. All experimental results were simulated using a reaction model with eleven steps. ACKNOWLEDGMENTS The authors would like to thank mr Nebojša Begovi c ' from the Institute of General Physical Chemistry in Belgrade for help in finding the rate constants for new reactions. The present investigations are partially supported by the Ministry of Science Environmental Protection of the Republic of Serbia, Project no REFERENCES. R. Jiménez-Prieto, M. Silva, D. Perez-Bendito, Talanta 44, 463 (997). 2. Y. Ke, M. Wanhong, C. Ruxiu, L. Yhixin, G. Nanqin, Anal. Chim. Acta 43, 5 (2). 3. R. Jimenez-Prieto, M. Silva, D. Pérez-Bendito, Analyst 22, 287 (997). 4. N. Gan, R. Cai, Y. Lin, Anal. Chim. Acta 466, 257 (22). 5. J. Wang, S. T. Yang, R. X. Cai, Z. X. Lin, Z. H. Liu, Talanta 65, 799 (25). 6. V. Vukojevi c,' N. Peji c,' D. Stanisavljev, S. Ani c,' Analyst 24, 47 (999). 7. N. Peji c,' S. Blagojevi c,' S. Ani c,' V. Vukojevi c,' Anal. Bioanal. Chem. 38, 775 (25). 8. N. Peji c,' S. Ani c,' D. Stanisavljev, J. Pharm. Biomed. Anal. 4, 6 (26). 9. N. Peji c,' S. Blagojevi c,' S. Ani c,' V. Vukojevi c,' M. Mijatovi c,' J. C' iri c,' Z. Markovi c,' S. Markovi c,' Anal. Chim. Acta 582, 367 (27).. N. Peji c,' S. Blagojevi c,' S. Ani c,' Anal. Bioanal. Chem. 389, 29 (27).. N. Peji c,' S. Blagojevi c,' J. Vukeli c,' S. Ani c,' Bull. Chem. Soc. Jpn. 8, 942 (27). 2. J. Gao, G. Zhao, Z. Zhang, J. Zhao, W. Yang, Microchim. Acta 57, 35 (27). 3. R. Jimenez-Prieto, M. Silva, D. Perez-Bendito, Analyst 23, R8R (998). 4. J. Gao, H. Chen, H. Dai, D. Lu, J. Ren, L. Wang, W. Yang, Anal. Chim. Acta 57, 5 (26). 5. G. Hu, P. Chen, W. Wang, L. Hu, J. Song, L. Qiu, J. Song, Electrochim. Acta 52, 7996 (27). 6. J. Gao, J. Ren, W. Yang, X. Liu, H. Zang, Q. Li, H. Deng, J. Electoanal. Chem. 52, 57 (22). 7. P. E. Strizhak, O. Z. Didenko, T. S. Ivashchenko, Anal. Chim. Acta 428, 5 (2). 8. L. N. Tikhonova, A. S. Kovalenko, I. F. Labunskaya, Zh. Neorg. Khim. 33, 649 (988). 9. Z. Cupi c,' S. Ani c,' A. Terlecki-Baricevi c,' React. Kinet. Catal. Lett. 54, 43 (995). 2. A. Terlecki-Baricevi c,' Z. Cupi c,' S. Ani c,' Lj. Kolar- Ani c,' S. Mitrovski, S. Ivanovi c,' J. Serb. Chem. Soc. 6, 969 (995). 2. N. Peji c,' Z. Cupi c,' S. Ani c,' V. Vukojevi c,' Sci. Sintering 33, 7 (2). 22. M. Miloševi c,' N. Peji c,' Z. Cupi c,' S. Ani c,' Mater. Sci. Forum. 494, 369 (25). RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 9 29

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