Selective oxidation of light alkanes over Mo-based oxide catalysts

A highly reduced Keggin-type heteropolymolybdophosphate, H₃PMo₁₂O₄₀(Py), which was formed by the heat-treatment of pyridinium salt of H₃PMo₁₂O₄₀, can catalyze the propane oxidation to acrylic acid and acetic acid selectively. We propose a possible reaction mechanism for alkane oxidation, where protons and electrons on the reduced H₃PMo₁₂O₄₀ catalyst cooperate for activating molecular oxygen to form electrophilic oxygen species for alkane oxidation. It is also reported that Anderson-type heteropolycompounds linked with vanadyl cations VO²⁺ were able to be synthesized by hydrothermal reaction and showed good catalytic activity for the ethene oxidation to acetic acid.     

Selective photocatalytic oxidation of light alkanes over alkali-ion-modified V2O5/SiO2; kinetic study and reaction mechanism

Alkali-ion-modified silica-supported vanadium oxides are photocatalysts available in the field of photooxidation of light alkanes using molecular oxygen. The photooxygenated reaction was promoted over the catalyst under irradiation at steady state. Acetone formation on the photooxidation of propane was investigated over a rubidium-ion-modified silica-supported vanadium oxide that is the most effective catalyst. The kinetic analysis demonstrated that the rate-determining step is the reaction of propane on the lattice oxygen of the photoexcited VO4Rb species to yield the vanadium isopropoxide species. It was suggested that the photocatalytic active sites are occupied by photogenerated acetone during photoreaction at 333 K. Heating the photocatalyst bed drastically enhanced not only product yield but also the selectivity to propionaldehyde that is a minor product in the photooxidation at 333 K. The product distribution of photoassisted oxidation of propane was described by Boltzmann's distribution of stabilization energy of the intermediates: an isopropoxide-like one for the precursor of acetone and an n-propoxide-like one for the precursor of propionaldehyde.     

Oxidation of n-propanol over vanadium oxide catalysts

The kinetics of catalytic oxidation of n-propanol on V₂O₅ and V₂O₅ modified with BeO, MgO, CaO and SrO has been investigated. A high selectivity of the oxidation to propionaldehyde was observed. The activation energies of the reaction and of the exchange of oxygen in these catalysts with molecular oxygen and CO₂ were found to change in parallel.

---

- V₂O₅ V₂O₅ BeO, CaO, MgO SrO. . .

     

钨基催化剂上烷烃异构化研究进展

随着人们对汽油质量的要求越来越高,烷烃异构化越来越受到重视,尤其是长链烷烃异构化,因此研究高性能的异构化催化剂具有非常重要的意义。本文综述了一类用于长链烷烃异构化的新型催化剂-钨基催化剂的研究进展,介绍了此类催化剂的制备、异构化反应,简要介绍了其反应机理。并分析了此类催化剂今后的发展趋向和应用前景。     

Complete oxidation of ethanol over vanadium based catalysts

V2O5/γ-Al2O3-TiO2 catalysts were prepared by the mixing sol-gel and co-impregnation method. The performance of the catalysts for complete oxidation of ethanol was performed in a conventional fixed-bed quartz reactor. And the effects of support, preparation methods and vanadium content have been investigated. The results showed that 5% V2O5 catalyst supported on γ-Al2O3-TiO2 possessed the best ethanol conversion under the considered temperature. This may be ascribed to the highly dispersible active component, mutual function between the active component and the carriers. The nature of the best performance for 5%V/γ-Al2O3-TiO2 catalyst may be related to the high V4+ amounts on the surface. And the surface V4+ species may play an important role in the formation of active site for the total ethanol oxidation.     

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.     

Formation of carbon nanofilaments from C6-C16 alkanes over nickel-containing catalysts

The properties of 85%Ni/Al₂O₃ and NiO/Sibunit series catalysts have been studied in the formation of carbon nanofilaments from n-hexane, n-undecane, and n-hexadecane. In the temperature range 450–600°C, the reactivity of these hydrocarbons decreases in the following order: n-hexane > n-undecane > n-hexadecane. The deposition rate of carbon nanofilaments from n-hexane or n-undecane over the 85%Ni/Al₂O₃ catalyst in the range 450–600°C slightly depends on the reaction temperature. The activation energy of the formation of carbon nanofilaments from n-hexane is 10 kcal/mol and that from n-undecane, 13.5 kcal/mol. The rate-limiting reaction is the interaction of a paraffin molecule with the nickel metal surface. As the reaction temperature increases to 700°C, the formation rates of carbon nanofilaments from the C₆-C₁₆ paraffin hydrocarbons are equalized, which is associated with the increase in the intensity of thermal pyrolysis reactions of alkanes. The resulting olefins, first of all, ethylene and propylene, become major contributors to carbon formation.     

Isomerization of light alkanes: preparation and characterization of platinum promoted sulfated zirconia catalysts

Summary Platinum-promoted sulfated zirconia catalysts active in n-hexane isomerization were prepared in a one-step synthesis and characterized. The crystallinity and sulfur contents depend mainly on the calcination temperature. The stability of the sulphate in the presence of hydrogen is reduced by the presence of Pt.     

Photooxidation of alkanes by oxygen catalyzed by CuCl2 in acetonitrile

The irradiation of a solution of anhydrous CuCl₂, taken as a photocatalyst, and an alkane in acetonitrile in the air with visible light (>320 nm) leads to the formation of alcohol and ketone products.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 698–699, March, 1990.     

CH4 oxidation over palladium and vanadium containing catalysts

The kinetics of total oxidation of CH₄ over a complex vanadium catalyst with and without Pd additives and over silica-supported palladium has been studied. The addition of palladium increases the initial reaction rate but as catalysis progresses, the activity decreases to the level of an unpromoted catalyst. Palladium additives do not affect the mechanism of CH₄ oxidation.

---

, , . , . .

     

Catalytic aromatization of light alkanes

Experimental data on the application of pentasil-type zeolites in the aromatization of lowmolecular-weight alkanes are surveyed. Examples of the transformation of ethane and propane into aromatics over pentasils containing Zn, Ga, or Ga-Pt are given. An important role of Pt in the formation of active and selective Ga-Pt catalysts for light alkane aromatization is shown.     

Photooxidation of Methane over TiO2

Fourier‐transform infrared spectroscopy has been employed to investigate the adsorption and photo‐oxidation of CH₄ over powdered TiO₂. The interaction between the CH₄ and TiO₂ surface is weak. It is found that no CH₄ molecules are adsorbed on the surface at 35 °C in a vacuum. Under UV irradiation, CH₄ decomposes to form CO_(a), CO_2(g), H20_(a), and HCOO_(a) in the presence of O₂. The photoreaction rate is retarded and only small amounts of CO_(a) and HCOO_(a) are formed in the absence of O₂. It is observed that the oxygen atoms of O₂ are incorporated into these photoproducts as ¹⁸O₂ is used. The major ¹⁸O‐containing products are C¹⁸O_(a), C¹⁸O_2(g), H₂ ¹⁸O_(a), HC¹⁶O¹⁸O_(a), and HC¹⁸O¹⁸O_(a) after 180 min UV irradiation. However, the extent of ¹⁸O incorporating into the adsorbed formate is dependent on UV irradiation time. In the early stage of UV irradiation HC¹⁶O¹⁶O_(a) is the major formate form indicating the involvement of TiO₂ lattice oxygens for its formation, but HC¹⁸O¹⁸O_(a) becomes the major one after 180 min indicating the involvement of ¹⁸O₂. Formate on TiO₂ further photodecomposes to CO_2(g), but not to CO_(a). CO_(a) formation is directly from CH₄ photodecomposition with the participation of TiO₂ lattice oxygens and O₂.     

After-effect of light in the photocatalytic oxidation of isobutene on immobilized vanadium oxide catalysts

A photocatalytic after-effect of visible and UV light in isobutene oxidation to acetone on immobilized vanadium oxide catalysts has been established. It is ascribed to the formation of labile active sites from coordinatively unsaturated V(V) compounds upon irradiation.

---

. - - .

     

Photooxidation of polyolefins and their light stability

It is shown that all peculiarities of polypropylene photooxidation and alteration of its mechanical properties in this process are a process of second-order termination reaction. The influence of natural conditions (varied temperature and light intensity) on this process are considered.     

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.     

Dehydrogenation of isobutane in the presence of carbon dioxide over supported vanadium oxide catalysts

Summary The dehydrogenation of isobutane to isobutene in the presence of carbon dioxide was carried out over supported vanadium oxide catalysts. The influence of the support on the catalytic performance was investigated. The isobutane conversion and isobutene selectivity in the presence of carbon dioxide were compared with the results obtained during the dehydrogenation reaction in the presence of helium (inert gas). The catalysts were characterized by temperature-programmed techniques (TPR, TPD-NH₃, TPD-CO₂).     

Photooxidation of alkanes and benzene by polyvanadate in CF3CO2H

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, p. 2461, October, 1990.     

Chemical analysis of vanadium pentoxide catalysts

Reliable procedures are described for the analysis of alkali metal sulphate-promoted vanadium pentoxide catalysts supported on silica gel. Vanadium and alkali metals are determined by flame atomic absorption spectrometry in suitable dilutions of solutions obtained by digestion with sulphuric and hydrofluoric acids. “Free acidity” is determined by dissolution of the samples in alkali and back-titration with acid ; corrections for V₂0₅ acidity are included. Relative standard deviations are about 2.5% for metal contents of3–5%($\text{w}\text{w}$).