Nitric oxide disproportionation on chabazite tuff

The catalytic activity of a chabazite tuff in the reaction 4NON₂O+N₂O₃ was investigated in flow conditions at temperatures between –78 °C and +85 °C. The Ca or Na enriched samples are much more active than the natural tuff; the steady state NO conversion increases with decreasing temperature.

---

4NON₂O+N₂O₃ –78°C +85°C. , Ca Na , ; NO .

     

Catalytic oxidation of hydrogen on platinum

Using the thermochemical approach to interpret the kinetics of heterogeneous reactions and the mechanism of congruent dissociative decomposition of solids developed in the 1980s and (re)analyzing the experimental data available in the literature over the last 90 years, a novel mechanism for the catalytic oxidation of H₂ by PtO₂ is proposed. In place of the conventional Langmuir–Hinshelwood and Eley–Rideal adsorption reaction mechanisms, our model is based on the reactions: PtO₂(s) + 2H₂ ? Pt(g) + 2H₂O and Pt(g) + O₂ ? PtO₂(g) → PtO₂(s). The first reaction determines the kinetics of H₂ oxidation and the second determines the kinetics of restoration of the PtO₂ layer. Thermochemical consideration of kinetic features of this model enables (for first time in the history of this reaction) the enthalpy and equilibrium constants for H₂ oxidation on platinum to be calculated. The results are in good agreement with experimental data. In addition, the proposed mechanism explains the origin of the surface-retexturing effect, the impact of autocatalysis, the influence of H₂O vapor on oxidation rate, and the three-fold variation of the Arrhenius E parameter with temperature. This all convincingly demonstrates the value of the thermochemical approach in interpreting heterogeneous reactions.     

Liquid hydrogen in protonic chabazite

Due to its fully reversible nature, H(2) storage by molecular adsorption could represent an advantage with respect to dissociative processes, where kinetic effects during the charging and discharging processes are present. A drawback of this strategy is represented by the extremely weak interactions that require low temperature and high pressure. High surface area materials hosting polarizing sites can represent a viable way toward more favorable working conditions. Of these, in this contribution, we have studied hydrogen adsorption in a series of zeolites using volumetric techniques and infrared spectroscopy at 15 K. We have found that in H-SSZ-13 zeolite the cooperative role played by high surface area, internal wall topology, and presence of high binding energy sites (protons) allows hydrogen to densify inside the nanopores at favorable temperature and pressure conditions.     

Correction to: Catalytic oxidation of hydrogen on platinum

Journal of Thermal Analysis and Calorimetry - Due to a fault (oversight) of the authors, L’vov BV, Galwey AK, in Fig 1 of the article: ‘Catalytic oxidation of hydrogen on...     

Microbial oxidation of mixtures of methylmercaptan and hydrogen sulfide

Refinery spent-sulfidic caustic, containing only inorganic sulfides, has previously been shown to be amenable to biotreatment withThiobacillus denitrificans strain F with complete oxidation of sulfides to sulfate. However, many spent caustics contain mercaptans that cannot be metabolized by this strict autotroph. An aerobic enrichment culture was developed from mixedThiobacilli and activated sludge that was capable of simultaneous oxidation of inorganic sulfide and mercaptans using hydrogen sulfide (H₂S) and methylmercaptan (MeSH) gas feeds used to simulate the inorganic and organic sulfur of a spent-sulfidic caustic. The enrichment culture was also capable of biotreatment of an actual mercaptancontaining, spent-sulfidic caustic but at lower rates than predicted by operation on MeSH and H₂S fed to the culture in the gas phase, indicating that the caustic contained other inhibitory components.     

Liquid-phase oxidation of hydrogen sulfide in centrifugal bubbling apparatus

Liquid-phase oxidation of H₂S in centrifugal-bubbling apparatus in the presence of catalysts [manganese(II) chloride, cobalt phthalocyanine disulfonic acid, and a catalytic system including cobalt phthalocyanine disulfonic acid and MnCl₂] was studied.     

Catalytic oxidation of monosubstituted phenols by hydrogen peroxide

Studies of kinetic peculiarities in hydroxylation of phenols by H₂O₂ in the presence of ferric sulfate have revealed general regularities of this process. A scheme of this process is suggested accounting for the stepwise conversion of Fe³⁺ into various complex forms. The reaction is suggested to take place in the coordination sphere of Fe³⁺.

---

H₂O₂ . . , Fe³⁺ .

     

First enantioselective iron-porphyrin-catalyzed sulfide oxidation with aqueous hydrogen peroxide

The asymmetric oxidation of sulfides by H(2)O(2) to give optically active sulfoxides (ee up to 90%) was carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts.     

Mechanism of gas-phase oxidation of hydrogen sulfide at high temperatures

A kinetic model of oxidation of hydrogen sulfide is proposed. The model contains 201 elementary stages, 23 particles, and satisfactorily describes the experimental data in a wide range of temperatures and pressures.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1956–1966, September, 1990.We would like to thank M. G. Neigauz, the author of the kinetic program, for providing the program and constant assistance in performing the calculations.     

Combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash

Hydrogen sulfide is highly toxic to benthic organisms and may cause blue tide with depletion of dissolved oxygen in water column due to its oxidation. The purpose of this study is to reveal the combined adsorption and oxidation mechanisms of hydrogen sulfide on granulated coal ash that is a byproduct from coal electric power stations to apply the material as an adsorbent for hydrogen sulfide in natural fields. Sulfur species were identified in both liquid and solid phases to discuss removal mechanisms of the hydrogen sulfide with the granulated coal ash. Batch experiments revealed that hydrogen sulfide decreased significantly by addition of the granulated coal ash and simultaneously the sulfate ion concentration increased. X-ray absorption fine structure analyses showed hydrogen sulfide was adsorbed onto the granulated coal ash and successively oxidized by manganese oxide (III) contained in the material. The oxidation reaction of hydrogen sulfide was coupling with reduction of manganese oxide. On the other hand, iron containing in the granulated coal ash was not involved in hydrogen sulfide oxidation, because the major species of iron in the granulated coal ash was ferrous iron that is not easily reduced by hydrogen sulfide.     

Redox mediators of hydrogen sulfide oxidation in reactions with cycloalkanes

An indirect electrochemical method for thiolation of cycloalkanes C₅–C₇ has been suggested. The method is based on a new approach to activation of hydrogen sulfide by redox mediators.     

Catalytic oxidation of hydrogen in solutions of metal complexes

The kinetics of H₂ oxidation at 25°C in solutions of Pd-histidine complexes has been studied and a reaction mechanism suggested for the explanation of the experimental data. In terms of this mechanism, the correlation between the activities of homogeneous catalysts and reactant-catalyst bond energies are considered. The oxygen-catalyst bond energy proves to be a determining factor similarly as in heterogeneous catalytic oxidation.

---

25°C Pd , ; .

     

Chemisorption of hydrogen sulfide on lead sulfide

The hydrogen sulfide chemisorption on lead sulfide at 22–100°C is studied by static testing in a vacuum and by pulsed chromatography. It is established that H₂S is sorbed in reversible and irreversible forms and that the process is accompanied by the sample charging. Irreversibly sorbed hydrogen sulfide is removed by heating the sample in a vacuum or in an inert-gas stream at temperatures exceeding the adsorption temperature by 30–50°C.     

Effect of partial charge parametrization on the fluid phase behavior of hydrogen sulfide

The effect of partial charge parametrization on the fluid phase behavior of hydrogen sulfide is investigated with grand canonical histogram reweighting Monte Carlo simulations. Four potential models, based on a Lennard-Jones + point charge functional form, are developed. It is shown that Lennard-Jones parameters can be tuned such that partial charges for the sulfur atom in the range -0.40 < q(s) < -0.252 will lead to an accurate reproduction of experimental vapor-liquid equilibria. Each of the parameter sets developed in this work are used to predict the pressure composition behavior H2S-n-pentane at 377.6 K. While the mixture calculation provides a means of reducing the number of candidate parameter sets, multiple parameter sets were found to yield an excellent reproduction of both the pure component and mixture phase behavior.     

Catalytic activity of transition metal silicides in hydrogen oxidation

The catalytic activity of transition metal silicides in H₂ oxidation is much higher compared to metal-like carbides, which can be due to the lower electronegativity of silicon compared to carbon.

---

, , .

     

Catalytic oxidation of hydrocarbons with hydrogen peroxide by vanadium-based polyoxometalates

Vanadium compounds have attracted much attention because they have widely been used for homogeneous, heterogeneous, industrial, and biological oxidation processes with alkyl hydroperoxides, H₂O₂, and O₂. The present review summarizes recent developments for homogeneous and heterogeneous liquid-phase oxidation of hydrocarbons with H₂O₂ catalyzed by vanadium complexes and vanadium-based polyoxometalates including our recent studies on selective oxidation of hydrocarbons with H₂O₂ catalyzed by divanadium-substituted polyoxotungstates, [γ-SiW₁₀O₃₆V₂(μ-OH)₂]^4? (I) and [γ-PW₁₀O₃₆V₂(μ-OH)₂]^3? (II).     

Selective oxidation of hydrogen sulfide over potassium promoted vanadium oxide on a alumina catalysts

The effect of potassium addition to alumina supported vanadium catalysts on the catalytic activity for the selective oxidation of H₂S is investigated. XRD, XPS and XANES have been used to characterize a series of K-V/Al₂O₃catalysts. The enhanced sulphur yield has been correlated with the crystallinity of vanadium. This revised version was published online in August 2006 with corrections to the Cover Date.