Vanadium hydroxylation catalysts

The vanadium oxide species is formed on the surface of the oxide support during the preparation of supported vanadium oxide catalysts. This is evident by the consumption of surface hydroxyls (OH) [5] and the structural transformation of the supported metal oxide phase that takes place during hydration-dehydration studies and chemisorption of reactant gas molecules [6]. Recently, a number of studies have shown that the structure of the surface vanadium oxide species depends on the specific conditions that they are observed under. For example, under ambient conditions the surface of the oxide supports possesses a thin layer of moisture which provides an aqueous environment of a certain pH at point of zero charge (pH at pzc) for the surface vanadium oxide species and controls the structure of the vanadium oxide phase [7]. Under reaction conditions (300-500 C), moisture desorbs from the surface of the oxide support and the vanadium oxide species is forced to directly interact with the oxide support which results in a different structure [8]. These structural... 

Catalysts for ethylene/carbon monoxide copolymerisation were initially obtained from Ni(II) derivatives, such as K2Ni(CN)4 and (w-Bu4N)2 Ni(CN)4, and Pd(II) derivatives, such as [(w-Bu3P)PdCl2]2, Pd(CN)2 and HPd(CN)3, often combined with alcohol or protonic acid as a cocatalyst [241]. It must be emphasised that, in contrast to titanium-, zirconium- or vanadium-based catalysts, nickel- and palladium-based catalysts tolerate polar functional groups (including hydroxyl, carboxylic and sulfonic groups)... 

In phenol hydroxylation, remarkable selectivities to single products have been achieved using vanadium heteropolyacid catalysts.485 The use of the ZSM-5 titanium silicalite (TS-1)483 permits the oxidation of phenol to catechol and hydroquinone to be carried out on an industrial scale with a higher selectivity at a greater conversion of substrate that was not previously possible with strong acid catalysts. 

Molinari R., Lavorato C., Poerio T. 2012. Performance of vanadium based catalyst in a membrane contactor for the benzene hydroxylation to phenol. Applied Catalysis A General 417--H8 87-92. 

Molinari, R., Argurio, P., Poerio, T. (2012). Vanadium (III) and vanadium (IV) catalysts in a membrane reactor for benzene hydroxylation to phenol and study of membrane material resistance. Applied Catalysis A General, 437—438, 131—138. 

This reaction was first demonstrated over V, Mo and W oxides [6]. At 823 K vanadium oxide provided phenol selectivity up to 71%, which was much higher than it had been ever achieved with O2. This result stimulated further efforts in searching for more efficient catalytic systems. As a result, in 1988 three groups of researchers [7-9] have independently discovered ZSM-5 zeolites to be the most efficient catalysts. They allowed the reaction to proceed at much lower temperature (573-623 K) with nearly a 100% selectivity. Later, more complex aromatic compounds were also hydroxylated in this way [2]. 

The incorporation of vanadium(V) into the framework positions of silicalite-2 has been reported by Hari Prasad Rao and Ramaswamy . With this heterogeneons oxidation catalyst the aromatic hydroxylation of benzene to phenol and to a mixtnre of hydroqninone and catechol conld be promoted. A heterogeneons ZrS-1 catalyst, which has been prepared by incorporation of zirconinm into a silicalite framework and which catalyzes the aromatic oxidation of benzene to phenol with hydrogen peroxide, is known as well in the literature. However, activity and selectivity were lower than observed with the analogous TS-1 catalyst. 

Oxidation of methylated sugars with nitric acid was used extensively by early workers for locating the position of unsubstituted hydroxyl groups.116 Cleavage of carbon-carbon bonds appears to be facilitated by the presence of such catalysts as vanadium salts. As hot nitric acid acts as a hydrolyzing agent as well as an oxidant, oligo- and poly-saccharides may be used directly. 

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