Vanadium-titanium oxide system

VANADIUM-TITANIUM OXIDE SYSTEM IN p-PICOLINE OXIDATION... 

Abruna HD (1991) X-ray Absorption Spectroscopy in the Study of Electrochemical Systems. In Electrochemical Interfaces. Abruna HD (ed) VCH Publishers, New York Albertini G, Carsughi F, Casale C, Fiori F, La Monaca A, Musci M (1993) X-ray and neutron small-angle scattering Investigation of nanophase vanadium-titanium oxide particles. Phil Mag B 68 949-955 Alexandrowicz Z (1993) How to reconcile classical nucleation theory with cluster-cluster aggregation. Physica A 200 250-257... 

Methylpyridines are easily converted into the corresponding nitriles. The ammoxidation of 3-methylpyridine to nicotinonitrile has been particularly extensively investigated, mainly because of the importance of the nitrile as precursor of vitamins. The catalysts used are mostly vanadium-containing oxides, e. g. vanadium-titanium oxide [86], vanadium-zirconium oxide [87], or multicomponent systems [30,88]. Yields of more than 90% at nearly complete conversion were recently reported (e. g. 100% selectivity for vanadium oxide on titania (anatase) catalysts with V2O5 loading < 3.4 mol% [89]. 

In this paper, we wish to report on the selective oxidation of 5-hydroxymethylfurfural to 2,5-furan-dicarboxaldehyde using vanadium oxide supported on titanium oxide with different vanadium loadings. If we take into account the large differences in the activation energies reported over V2O5 in the oxidation sequence benzyl alcohol --> benzaldehyde (Eg = 26 kJ/mol) and benzaldehyde > benzoic acid (Eg = 55 kJ/mol) [10], those catalytic systems were then expected to stop at the aldehyde stage by working at low temperatui e. 

A beat exchanger system installed on the coolant fluid circuit is used to produce high-pressure steam (6.10 Pa absolute. The catalyst is a mixture of vanadium and titanium oxides deposited on an inert, non-porous support The molar yield of phthalic anhydride is 74 per cent of stoichiometry, using 95 per cent o-xylene. 

Many heterogeneous catalytic systems have been developed and applied to ammoxidation reactions. Vanadium-containing oxides are preferred as supported, bulk, or multicomponent catalysts for the ammoxidation of aromatic or heteroaromatic compounds. Favored supports are titanium oxide (anatase) [18,19], zirconium oxide [20,21], tin oxide [22], or mixed supports such as titanium-tin oxide [23]. Catalytic systems used as bulk materials include vanadium-phosphorus oxides [24], crystalline vanadium phosphates [25], and vanadium oxide combined with antimony oxide [26] or molybdenum oxide [27]. Other important catalysts include multicomponent systems such as KNiCoFeBiPMoO c on silica... 

Mitsubishi Rayon Co. of Japan also reported a manufacture of methyl methacrylic acid or its methyl ester from a catalytic oxidation of propionic acid or its methyl ester with titanium-vanadium-phosphorous-oxide (PVTiO) as its catalytic system. This reaction is very similar to the propionate-formaldehyde route except that it does not involve use of formaldehyde in the process. The reaction mechanism of this process is still unknown. 

As a heterogeneous liquid phase reaction system, processes utilizing molecular oxygen as an oxidant and metal oxide of vanadium, titanium, and manganese as cocatalysts were reported (Scheme... 

Bond, G., Sarkany, A. and Parfitt, G. (1979). The Vanadium Pentoxide-titanium Dioxide System. Structural Investigation and Activity for the Oxidation of Butadiene, J. Catal., 57, pp. 476-493. 

One-electron reduction or oxidation of organic compounds provides a useful method for the generation of anion radicals or cation radicals, respectively. These methods are used as key processes in radical reactions. Redox properties of transition metals can be utilized for the efficient one-electron reduction or oxidation (Scheme 1). In particular, the redox function of early transition metals including titanium, vanadium, and manganese has been of synthetic potential from this point of view [1-8]. The synthetic limitation exists in the use of a stoichiometric or excess amount of metallic reductants or oxidants to complete the reaction. Generally, the construction of a catalytic redox cycle for one-electron reduction is difficult to achieve. A catalytic system should be constructed to avoid the use of such amounts of expensive and/or toxic metallic reagents. 

The most widely studied transition metal is titanium. At various times, all oxidation states of titanium (II, III, IV) have been proposed for the active site of titanium-based initiators. Most of the evidence points to titanium (HI) as the most stereoselective oxidation state, although not necessarily the most active nor the only one [Chien et al., 1982]. (Data for vanadium systems indicate that trivalent vanadium sites are the syndioselective sites [Lehr, 1968].) Initiators based on the a-, y-, and 8-titanium trihalides are much more stereoselective (iso-selective) than those based on the tetrahalide or dihalide. By itself, TiCl2 is inactive as an initiator but is activated by ball milling due to disproportionation to TiCl3 and Ti [Werber et al., 1968]. The overall stereoselectivity is usually a-, y-, 8-TiCl , > TiCL > TiCLj P-TiCl3 [Natta et al., 1957b,c],... 

Isocyanate formation through multiple bond metathesis of C02 with carbodiimide has been also demonstrated [112]. This transformation can be promoted by titanium isopropoxide, at 383 K, in THF as solvent. It is worth noting that the reverse process, which opens an entry into carbodiimide synthesis, is a well-known process that is catalyzed by several other systems, including trialkylphosphine oxides [113] or vanadium-oxo or -imido complexes [114]. 

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