Recent advances in transition metal catalyzed oxidation of organic substrates with molecular oxygen.

Oxidative dehydrogenation of ethane and propane : How far from commercial implementation?

This paper summarizes the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts. The acid-base character of metal oxide support influences the dispersion of vanadium on the surface of the support, as well as the nature of the vanadium species. The reducibility and structure of surface vanadium oxide species and the acid-base character of catalysts, in addition to their catalytic properties in the ODH of C2–C4 alkanes, strongly depend on the metal oxide used as support and the vanadium loading. In this way, it appears that tetrahedral V5+-species are active and selective sites in the ODH of C2–C4 alkanes. The effect of the coordination number and aggregation state of surface vanadium oxide species, and the presence of acid/base sites on the catalytic behavior of supported vanadium oxide catalysts are discussed. It is concluded that these are important factors that must be considered to develop selective catalysts in ODH reactions.

Oxidative dyhydrogenation of short chain alkanes on supported vanadium oxide catalysts

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1-xMxO2±δ The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25 The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2

Structure and Photocatalytic Activity of Ti1-xMxO2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

In the quest to discover the properties of planar semiconductors, two-dimensional molybdenum trioxide and dichalcogenides have recently attracted a large amount of interest. This family, which includes molybdenum trioxide (MoO 3 ), disulphide (MoS 2 ), diselenide (MoSe 2 ) and ditelluride (MoTe 2 ), possesses many unique properties that make its compounds appealing for a wide range of applications. These properties can be thickness dependent and may be manipulated via a large number of physical and chemical processes. In this Feature Article, a comprehensive review is delivered of the fundamental properties, synthesis techniques and applications of layered and planar MoO 3 , MoS 2 , MoSe 2 , and MoTe 2 along with their future prospects.

Two-Dimensional Molybdenum Trioxide and Dichalcogenides

Chromium Oxide/Alumina Catalysts in Oxidative Dehydrogenation of Isobutane☆

Oxidative dehydrogenation of propane has been studied on V2O5/TiO2 and MoO3/TiO2 catalysts, consisting of 1 and 5 monolayers of the deposited oxides, promoted with Li, K and Rb cations. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and by isopropanol decomposition, a probe for acid-base properties. For both types of catalysts, irrespective of the vanadium or molybdenum content, the total activity in oxidative dehydrogenation of propane decreased for the promoted catalysts in the sequence: non-promoted ≥ Li > K > Rb-promoted catalyst. The propene yields and selectivities at equal conversion increased in the same order. The same sequence was also observed for the increase in the rate of acetone formation and the decrease in the rate of propene formation in the isopropanol decomposition on the promoted catalysts. It is proposed that the alkaline promoters decrease the acidity and increase the basicity of the catalysts, and hence facilitate desorption of propene from the catalyst surface, preventing it from further oxidation to carbon oxides. The XPS data suggest that the alkaline promoters increase the dispersion of the vanadia or molybdena phase in the high vanadium or molybdenum content catalysts.

Effect of alkaline promoters on catalytic activity of V2O5/TiO2 and MoO3/TiO2 catalysts in oxidative dehydrogenation of propane and in isopropanol decomposition

Oxidative Dehydrogenation of Propane on NixMg1−xAl2O4 and NiCr2O4 Spinels

Oxidative dehydrogenation of propane over V 2 O 5 /TiO 2 (anatase) catalysts has been studied by steady-state and transient kinetic methods. Steady-state experiments were carried out by measuring conversions and selectivities for various feed compositions including C 3 H 8 , O 2 and He, and for various contact times, at 225, 250 and 280 °C. Transient tests consisted in submitting a fixed bed of catalyst to a constant flow rate of feed with alternating concentration steps of O 2 in He and C 3 H 8 in He, separated with steps of pure He. The influence of reaction temperature and partial pressure of C 3 H 8 on the concentrations of the reaction products (C 3 H 6 , CO, CO 2 , H 2 O) has been studied in this way in the temperature range 166–446 °C. The results obtained by both methods could be interpreted on the basis of a mechanism in which the C 3 H 6 formation proceeds through a Eley–Rideal sequence of steps, i.e. without participation of the adsorbed propane species. On the basis of the above results, two reaction models have been compared, considering the lattice oxygen as the only oxygen species which participate in the reaction. In the first model, different reaction orders with respect to concentration of the surface oxide species have been considered, for the selective ODH reaction (order=1) and for total combustion reactions (order=2). In the second model, two different types of lattice oxygen were assumed, one of them giving rise to selective oxidation, the other to total combustion products. Both models provided equally good representation of the experimental results, but the first one seems more plausible on the basis of additional arguments. Kinetic constants for both models (activation energies, pre-exponential factors) obtained on the basis of steady-state results are given.

Kinetics of the propane oxidative dehydrogenation on vanadia/titania catalysts from steady-state and transient experiments

Oxidative dehydrogenation, ODH, of isobutane has been performed on chromia supported on SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 and MgO The potassium promoted (K/Cr= 01) catalysts have also been examined The supported chromia has been found active in the ODH of isobutane at relatively low temperatures 200–400°C, the total activity and selectivity to isobutene depending on the nature of the support and the potassium presence The highest selectivities to isobutene (ca 70% at 5% conversion) and the isobutene yields of ca 9% have been obtained for Cr/O x TiO 2 and K-promoted CrO x /Al 2 O 3 preparations

K. Wcisło

Papers

Chromium Oxide/Alumina Catalysts in Oxidative Dehydrogenation of Isobutane☆

Effect of alkaline promoters on catalytic activity of V2O5/TiO2 and MoO3/TiO2 catalysts in oxidative dehydrogenation of propane and in isopropanol decomposition

Oxidative Dehydrogenation of Propane on NixMg1−xAl2O4 and NiCr2O4 Spinels

Kinetics of the propane oxidative dehydrogenation on vanadia/titania catalysts from steady-state and transient experiments

Oxidative dehydrogenation of isobutane on supported chromia catalysts