Relaxation kinetic studies of sulfur dioxide oxidation over vanadium catalyst

Relaxation processes of approaching a steady state of the catalytic system in sulfurous anhydride oxidation over a vanadium catalyst have been studied by a transient response method. It is shown that the experimental results can be interpreted in terms of a two-route mechanism.

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Kinetics and mechanisms of the oxidation of sulfur dioxide over titanium dioxide and nickel oxide

The reactions between SO₂ and O₂ were carried out in the presence of TiO₂ and NiO under various partial pressures of SO₂ and O₂ at temperatures from 240 to 330°C. TiO₂ and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO₂ pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10^?4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first-order kinetics for TiO₂ and NiO, respectively. A reaction mechanism to explain the data was suggested. The quantities of anionic vacancies in TiO₂ surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics.     

ESR studies of slow relaxations of the rate of sulfur dioxide oxidation on vanadium catalyst

Slow changes in the rate of the title reaction are shown to be due to pahse transformations of the active component, in particular, the agglomeration or crystallization of vanadyl complexes. The possible mechanism of these phenomena is discussed.

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Kinetics of methanation of carbon dioxide on a nickel catalyst

The kinetics of hydrogenation of CO₂ to methane on an NKM-4A nickel-containing catalyst was studied in a wide range of change of partial pressures of hydrogen and carbon dioxide at 498–543 K. It was shown that when hydrogen is replaced by deuterium in the reaction, a reverse kinetic isotope effect is observed. The kinetic equation of the reaction was derived and a stepwise scheme is proposed which includes the involvement of oxygen-containing intermediates in the process without preliminary dissociation of CO₂.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 26, No. 5, pp. 620–624, September–October, 1990.     

Interaction between sulfur dioxide and a co-reduced alumino-ferrous catalyst

From gamma-resonance spectroscopy investigations it was shown that as a result of absorption of SO₂ from moist air by a CO-reduced alumino-ferrous catalyst SO₂ is irreversibly bound to form hydrated iron sulfate at 393–523 K, and that CO molecules are in part reversibly substituted by SO₂ molecules in the Fe²⁺ coordination sphere at 573–723 K.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 220–225, May-June, 1992.     

Kinetics of oxidation of acrolein on a vanadium-molybdenum oxide catalyst

A kinetic study has shown that, in the range of low conversions, the reaction rate depends only on the partial pressure of oxygen. Comparison of the oxidation of acrolein and I-deuteroacrolein suggests that the splitting of the H–CO bond is not rate-limiting.

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Enhanced sulfur dioxide electrooxidation performance on a modified XC-72 carbon catalyst

Journal of Solid State Electrochemistry - Vulcan XC-72 is a carbon catalyst that is widely used in electrochemistry. The electrooxidation of SO2 plays a significant role in the domain of...     

Nonsteady-state kinetic model of sulfur dioxide oxidation on vanadium catalysts

Rate constants and activation energies of individual steps for the previously suggested mechanism of SO₂ oxidation on vanadium catalysts have been determined from experimental data on nonsteady-state kinetics.

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Kinetics of oxidation of methanol by chlorine dioxide

The kinetics of oxidation of methanol by chlorine dioxide has been investigated at 35 °C. The reaction is first order with respect to both substrate and chlorine dioxide. Molecular chlorine dioxide is the principal oxidant. The influence of various factors, e.g. ionic strength, inorganic salts, D₂O and temperature on the initial rate has been studied. The activation parameters have been calculated and a mechanism involving hydride abstraction has been suggested.

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Kinetics of oxidation of phenol with manganese dioxide

The kinetics of oxidation of phenol with manganese dioxide at pH 5.5±0.5 were studied. In the temperature range from 393 to 323 K the reaction is of second order, and it occurs in the kinetic mode with an energy of activation of 42.0 kJ/mol. In the temperature range from 333 to 353 K the reaction follows first-order equation and is controlled by external diffusion; the energy of activation is equal to 6.65 kJ/mol. The oxidation products are hydroquinone and 1,4-benzoquinone, the fraction of the latter being less than 10 mol %.     

Kinetics and equilibria of sulfur dioxide sorption in kapton polyimide

The kinetics and equilibria of SO₂ sorption in Kapton polyimide film have been measured at 25°C for pressures up to 58 cm Hg using a quartz spring balance. The observed equilibria are described well by the dual-mode model for sorption of penetrants in glassy polymers. Observed hysteresis in sorption-desorption cycling indicates that the diffusivity of SO₂ increases markedly with increasing local penetrant concentration in the polymer. The concentration dependence of the effective average diffusion coefficient is described well by an expression from dual-mode theory. The Langmuir component of the sorption population has an extremely low mobility compared to that of the Henry's law component; in fact, the so-called “total immobilization” limiting case, which assigns a zero diffusion coefficient to this component, appears to be satisfactory under the conditions studied. These results, coupled with published results for other penetrants, suggest that the degree of immobilization of the Langmuir population depends to a great extent on the condensability and/or the molecular size of the penetrant. Predictions of the SO₂ diffusion time lag and permeability in Kapton as functions of the upstream SO₂ pressure are presented and discussed in terms of the dual-mode theory.     

Kinetics and mechanism of the profound oxidation of vinyl chloride on a cobalt catalyst

A scheme of the mechanism is suggested and a kinetic model was obtained for the profound oxidation of vinyl chloride on a cobalt-chromium oxide catalyst. The kinetic and thermodynamic parameters of the reaction were determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 202–206, May-June, 1992.     

Kinetics of the vapor-phase oxidation of o-xylene over a vanadium oxide catalyst

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The catalytic and adsorption properties of the (Pt–Sn)/Al₂O₃ system have been studied. The results of benzene hydrogenation, cyclohexane dehydrogenation and temperature-programmed hydrogen desorption show that the introduction of tin into the Pt/Al₂O₃ catalyst significantly changes the dispersity and electronic state of supported platinum.

     

Kinetics and mechanisms of chlorine dioxide oxidation of tryptophan

The reactions of aqueous ClO2 (*) and tryptophan (Trp) are investigated by stopped-flow kinetics, and the products are identified by high-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry and by ion chromatography. The rates of ClO2 (*) loss increase from pH 3 to 5, are essentially constant from pH 5 to 7, and increase from pH 7 to 10. The reactions are first-order in Trp with variable order in ClO2 (*). Below pH 5.0, the reactions are second- or mixed-order in [ClO2 (*)], depending on the chlorite concentration. Above pH 5.0, the reactions are first-order in [ClO2 (*)] in the absence of added chlorite. At pH 7.0, the Trp reaction with ClO2 (*) is first-order in each reactant with a second-order rate constant of 3.4 x 10(4) M(-1) s(-1) at 25.0 degrees C. In the proposed mechanism, the initial reaction is a one-electron oxidation to form a tryptophyl radical cation and chlorite ion. The radical cation deprotonates to form a neutral tryptophyl radical that combines rapidly with a second ClO 2 (*) to give an observable, short-lived adduct ( k obs = 48 s(-1)) with proposed C(H)-OClO bonding. This adduct decays to give HOCl in a three-electron oxidation. The overall reaction consumes two ClO2 (*) per Trp and forms ClO2- and HOCl. This corresponds to a four-electron oxidation. Decay of the tryptophyl-OClO adduct at pH 6.4 gives five initial products that are observed after 2 min and are separated by HPLC with elution times that vary from 4 to 17 min (with an eluent of 6.3% CH 3OH and 0.1% CH 3COOH). Each of these products is characterized by mass spectrometry and UV-vis spectroscopy. One initial product with a molecular weight of 236 decays within 47 min to yield the most stable product, N-formylkynurenine (NFK), which also has a molecular weight of 236. Other products also are observed and examined.     

Hysteresis phenomena in sulfur dioxide oxidation over supported vanadium catalysts

Catalyst deactivation and hysteresis behavior in industrial SO₂-oxidation catalysts have been studied in the temperature region 350–480°C by combined in situ EPR spectroscopy and catalytic activity measurements. The feed gas compositions simulated sulfuric acid synthesis gas and wet/dry deNO_x'ed flue gas. The vanadium (IV) compound K₄(VO)₃(SO₄)₅ precipitated during all the investigated conditions hence causing catalyst deactivation. Hysteresis behavior of both the catalytic activity and the V(IV) content was observed during reheating.     

Kinetics of isobutylene oxidation on a Mo-Sb-Te-O (1 : 0.6 : 0.06) catalyst

Kinetics of isobutylene oxidation over a Mo-Sb-Te-O catalyst is studied in a flow-circulation system with the Korneichuk differential reactor. The reaction orders of methacrolein, acetic acid, acetone, and CO₂ formation, as well as the order of the overall reaction of isobutylene oxidation into methacrolein, with respect to oxygen and isobutylene are determined at 613–703 K and oxygen concentrations of (0.33–13.05) x 10⁻³ mol/1 and isobutylene (3.2–121.9) × 10⁻⁴ mol/1. The activation energies of these reactions are determined.     

Microbial removal of sulfur dioxide from a gas stream with net oxidation to sulfate

A study has been conducted of the feasibility of utilizing the sulfate reducing bacteriumDesulfovibrio desulfuricans and the chemoautotrophThiobacillus denitrificans as a basis of a microbial process for the removal of sulfur dioxide from a gas with net oxidation to sulfate. In reactors-in-series, SO₂ was reduced to H₂S in the first stage by D.desulfuricans. The H₂S was then stripped with nitrogen and sent to a second stage where it was oxidized to sulfate by T.denitrificans. A sulfur balance demonstrated complete reduction of SO₂ to H₂S in the first stage and complete oxidation of H₂S to sulfate in the second stage.     

FluoRuGel: a versatile catalyst for aerobic alcohol oxidation in supercritical carbon dioxide

FluoRuGel--a hybrid fluorinated silica glass doped with TPAP (tetra-n-propylammonium perruthenate)--is a versatile catalyst for the aerobic oxidation of different alcohols in dense phase CO(2) with marked stabilization and activity enhancement of perruthenate upon its confinement in the sol-gel fluorinated silica matrix. A brief competitive analysis shows large potential rewards.     

Kinetics of oxidation of ethylene to vinyl acetate using a homogeneous palladium complex catalyst

A kinetic study of the oxidation of ethylene to vinyl acetate using a palladium complex catalyst is reported. The effects of the ethylene partial press concentration and temperature on the rate of ethylene absorption were studied. The solubility of ethylene in acetic acid was determined at various sodi order with respect to the catalyst (PdCl₂) concentration and zero order with respect to the benzoquinone concentration. The dependence of the react basis of these data and the kinetic parameters were evaluated. The activation energy was found to be 14.6 kcal mol⁻¹.The effect of sodium acetate on the reaction rate was found to be complex, and an optimum sodium acetate concentration exists for a given set of condit increased with increase in temperature.