Determination of Kinetic Parameters in the interaction between Hydrogen Peroxide and Chromium (VI) Oxide (original) (raw)
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Inorganic Chemistry, 1994
The oxidation kinetics of aquated Cr(1I) by H202 is accelerated by a factor of 2-5 in the presence of organic and inorganic anions. The reaction was studied in detail as a function of anion concentration, temperature, and pressure for nine different anions. The kinetic data exhibit saturation behavior at high anion concentration, which can be assigned to the formation of a 1:l complex of the type CrII(H20)5(An)+. The rate and activation parameters are in line with an inner-sphere electron-transfer mechanism, in which both the inner-sphere complex formation and the electron-transfer rate constants are affected by the presence of the anion in the coordination sphere of Cr(I1). Trans-labilization effects and the increased electron density on the metal center are suggested to account for the accelerating effect of the investigated anions.
Reactions’ Mechanisms and Applications of Hydrogen Peroxide
American Journal of Physical Chemistry
Hydrogen peroxide is a key substance in the appearance of life and maintenance of the life-supporting conditions on the Earth. Electron transfer processes between H 2 O 2 and various reducers are of major interest for the environment, natural life, technology, etc. An overview of structure, proprieties and main reactions of hydrogen peroxide in model and real systems is presented. The authors try to find the answers to the following questions: why this substance has the unique and specific dual reduction-oxidation properties, what is the connection between its structure and reactions, what role it plays in the catalytic reduction processes occurring in the natural environment and technological systems, accompanied by the formation of intermediate compounds, active radicals, complete and partial charge transfer complexes, etc. The thermodynamic possibility of the synchronous two-electron transfer during the inner sphere reaction with the involvement of metal ion complexes capable of changing the valence by two units is discussed. The role of the partial charge transfer structures which combine the properties of the initial reagents and the expected reaction products is demonstrated. Such complexes can be decomposed both reversibly and irreversibly. In case when the single-electron transfer is thermodynamically preferable, the main oxidizing particle is OH-radical, capable to interact non-selectively with almost all the water-soluble organic substances. Special attention is paid to the photo initiation of peroxidase transformation processes. The results of our multi-annual research of these issues are reported.
International Journal of Chemical Kinetics, 2000
Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H 2 O 2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old . However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent.
Kinetics of heterogeneous decomposition of hydrogen peroxide
Journal of Inclusion Phenomena, 1986
Silica-alumina in the form of diethylamine (deam)-, dimethylamine (dmam)-, ethylamine (earn)-, ammonia (amm)-and aniline (an)-copper (II) complexes as well as deam-cobalt (II) complex have been used as potentially active catalysts for HzOz decomposition in an aqueous medium. The reaction was first order with respect to the H202 concentration and the rate constants (per g of dry silica-alumina) were determined. A coloured compound, a peroxo-metal complex, which formed at the beginning of the reaction in each case, was found to contain the catalytically active species. The activation energy and the change in the entropy of activation increased with the basicity of the ligands in the following order: an < amm < earn < dmam < deam, which is also the probability sequence for the formation of the activated complex. A reaction mechanism was proposed.
Use of mixed metal oxide as a catalyst in the decomposition of hydrogen peroxide
The decomposition of hydrogen peroxide in presence of some metal oxides as a heterogeneous & heterogenized catalyst has been investigated by measuring the evolution of oxygen at different time intervals in the temperature range 30-60 0 C. The catalytic activity is increased, an increase in the amount of catalyst and pH. The variation of H 2 O 2 at constant pH reveals that the values of k are nearly constant irrespective of H2O2. Various parameters have been calculated .The probable reaction mechanism have been suggested in which an intermediate surface complex is thought to be responsible for the enhancement of the decomposition of hydrogen peroxide.LaCrO 3 catalyst was characterized by XRD,TG/DTA,SEM,AFM.
Reaction of hydrogen peroxide with the oxochromium(IV) ion by hydride transfer
Inorganic Chemistry, 1993
Oxidation of hydrogen peroxide by pentaaquaoxochromium(IV), (H20)5Cr02+, in aqueous acidic solutions (0.10-1.0 M HC104) yields the superoxochromium(II1) ion (H20)5Cr002+. The same product is obtained in both the presence and the absence of oxygen. In 0.10 M HC104 the second-order rate constant at 25 OC is 190 f 10 L mol-' s-1 in 02-saturated solutions and 172 f 8 L mol-' s-' in Ar-saturated solutions, independent of acidity and ionic strength in the range 0.10-1.0 M (HC104/LiC104). In D20 as solvent the rate constant is kD = 53 f 3 L mol-' s-', resulting in the kinetic isotope effect kH/kD = 3.6. Experiments in the temperature range 6.8-38.4 OC yielded AH* = 25 f 3 kJ mol-' and AS* =-116 f 8 J mol-' K-I. A hydride-transfer mechanism is suggested for the oxidation of H202 by CrO2+. It involves the coordination of H202 to Cr(IV) prior to the hydride abstraction step. The reaction of HCrO4-with H202 under the same conditions also yields (H20)5Cr002+, which was identified by its characteristic UV spectrum. Possible mechanisms for these reactions are discussed.
Investigation of reduction kinetics of Cr 2O 7 2− in FeSO 4 solution
Chemical Engineering Journal, 2008
The kinetics of reduction of potassium dichromate (K 2 Cr 2 O 7 ) by Fe 2+ ions in sulfuric acid (H 2 SO 4 ) solution have been investigated under well-defined hydrodynamic conditions. The reaction has been monitored potentiometrically by measuring volt values between saturated calomel electrode and a Pt electrode. The effect of stirring rate, particle size, temperature, Fe 2+ and H + concentrations have been studied. It was found that the reaction kinetic model achieved in the study was chemical reaction control model. The reaction has been analyzed using kinetic equation t = (1 − (1 − x) 1/3 ). The rate has been found proportional to [Fe 2+ ] 0.5 [H + ] 0.5 and the apparent activation energy has been determined as 46.18 kJ mol −1 .