Ammoxidation toluene

Vanadia-titania ( 5 and other supported vanadia catalysts (9) can also be applied for the production of aromatic nitriles by ammoxidation of toluene and of the three xylene isomers allumina-supported V-Sb-based oxides seem to be the best catalysts (10). Detailed kinetic studies of toluene ammoxidation have been reported recently using different vanadia-titania catalysts ( 77,72). Ammonia inhibits toluene conversion, while benzonitrile yields (up to 80 % near 610 K) are mainly limited by... 

Selectivities and activities with molybdenum-based catalysts for toluene ammoxidation... 

Fig. 4. Mechanism of toluene ammoxidation to benzonitrile. Reprinted from Ref. (71), Copyright (1988), with permission from Elsevier Science.

The kinetic analysis of toluene ammoxidation reveals an additional reaction pathway. This reaction pathway is dominant at intermediate to low partial... 

Bruckner, A., Martin, A., Steinfeldt, N., Wolf, G.-U., and Liicke, B. Investigation of vanadium phosphorus oxide catalysts (VPO) during toluene ammoxidation new mechanistic insights by in-situ EPR. J. Chem. Soc., Faraday Trans. 1996, 92, 4257- 263. 

CavaUi, R, Cavani, R, El-Sawi, M., Manenti, I., and Trifiro, R Kinetic and mechanistic analysis of toluene ammoxidation to benzonitrile on vanadium-titanium oxides. Ind Eng Chem Res 26, 804-810 (1987). 

Martin, A., Zhang, Y, Zanthoff, H.-W.,Meisel, M., andBaems, M. The role of ammonium ions during toluene ammoxidation on a-(NH )j[(VO)j(PjO )J used as catalyst. Appl Catal A 139, L11-L16 (1996). http //en.wikipedia.org/wiki/Andrussow process Andrussow, L. Ange-w Chem 48, 593 (1935). 

Martin, A., Bemdt, H., Lilcke, B., and Meisel, M. Reaction pathway of benzonitri-le formation during toluene ammoxidation on vanadium phosphate catalysts. Topics Catal3, 377-386(1996). 

Ben2onitrile can be produced in high yield by the vapor-phase catalytic ammoxidation of toluene (76) ... 

So, our data and the known organic chemistry suggest, according to the literature (8,12), that ammoxidation and oxidation mechanisms are interplayed. We can consequently propose the following mechanism for the surface reactions relative to ammoxidation of toluene ... 

The IR study performed in static controlled atmospheres in the IR cell allowed us to identify a number of adsorbed intermediate and secondary products, together with the main reaction products in oxidation and ammoxidation of toluene and the three xylene isomers. Surface reactions schemes are proposed that account for most of the mechanistic features of the heterogeneously-catalyzed industrial reactions. Our data support the following conclusions ... 

Many substances can be partially oxidized by oxygen if selective catalysts are used. In such a way, oxygen can be introduced in hydrocarbons such as olefins and aromatics to synthesize aldehydes (e.g. acrolein and benzaldehyde) and acids (e.g. acrylic acid, phthalic acid anhydride). A selective oxidation can also result in a dehydrogenation (butene - butadiene) or a dealkylation (toluene -> benzene). Other molecules can also be selectively attacked by oxygen. Methanol is oxidized to formaldehyde and ammonia to nitrogen oxides. Olefins and aromatics can be oxidized with oxygen together with ammonia to nitriles (ammoxidation). 

Ammoxidation can be successfully applied to methyl aromatics (e.g. toluene and xylene) as it can to propene. However, the subject has not received much attention in the literature, mainly due to the fact that there are no important applications for aromatic nitriles at present. 

The kinetics of the toluene oxidation over Bi2Mo06 and a commercial Bi—Mo—P—O ammoxidation catalyst were investigated by Van der Wiele and Van den Berg [348]. A flow reactor was used at 450—550°C, 1—3 atm and varying feed rate, toluene and oxygen partial pressures. Benzaldehyde formation and combustion reactions are the main process the parallel-consecutive scheme which applies is... 

The selectivity of the ammoxidation of molecules like toluene and xylene is much higher than that of the oxidation of these compounds to aldehydes. The selectivity difference is more pronounced here than in case of propene. The initial selectivities of the propene oxidation and ammoxidation are practically the same, and the selectivity difference is mainly due to the high stability of acrylonitrile compared with acrolein. For aromatic (amm)oxidation, however, the initial selectivities also differ. Apparently, ammonia interacts with the catalyst in such a way that the activity for oxidation of the aromatic nucleus is reduced. 

A few contributions with respect to the ammoxidation of aromatic hydrocarbons that have appeared in the literature concern toluene and xylene. 

Ammoxidation, a vapor-phase reaction of hydrocarbon with ammonia and oxygen (air) (eq. 2). can be used to produce hydrogen cyanide (HCN), acrylonitrile, acetonitrile (as a by-product of acrylonitrile manufacture), methacrylonitrile, benzonitrile, and toluinitriles from methane, propylene, butylene, toluene, and xylenes, respectively. See also Acrylonitrile and Methacrylic Acid and Derivatives,... 

Ammoxidation of Aromatic Hydrocarbons. - The ammoxidation of toluene with V2O5, both pure and supported on A1203, was studied by Murakami et 0/.27,46,97,98 They conclude that the catalyst is bifunctional toluene is adsorbed oxidatively on V2O5, the oxidized product is stabilized as a benzoate ion on the alumina carrier and subsequently reacts with ammonia giving benzonitrile. It was observed that the oxidation state of the vanadium oxide was close to V204 and that benzaldehyde is probably the product formed in the initial step. 

Potential applications of superconducting cuprates in electronics and other technologies are commonly known. These cuprates also exhibit significant catalytic activity. Thus, YBa2Cu307 3 and related cuprates act as catalysts in oxidation or dehydrogenation reactions (Hansen et al. 1988 Halasz 1989 Mizuno et al. 1988). Carbon monoxide and alcohol are readily oxidized over the cuprates. NH3 is oxidized to N2 and H20 on these surfaces. Ammoxidation of toluene to benzonitrile has been found to occur on YBa2Cu307 (Hansen et al. 1990). 

Ammoxidation is also used for the manufacture of isophthalonitrile from m-xylene. The catalysts claimed in the patents are mixed oxides, e.g., of Mo, V, and Sb. The dinitrile is hydrogenated to m-xylylene diamine and m-diamino-dimethylcyclohexane, used for the production of the corresponding diisocyanates that are less toxic than toluene diisocyanate TDL A different use is for the production of tetrachloroisophthalonitrile, a potent fungicide. 

Thus, in ammonia synthesis, mixed oxide base catalysts allowed new progress towards operating conditions (lower pressure) approaching optimal thermodynamic conditions. Catalytic systems of the same type, with high weight productivity, achieved a decrease of up to 35 per cent in the size of the reactor for the synthesis of acrylonitrile by ammoxidation. Also worth mentioning is the vast development enjoyed as catalysis by artificial zeolites (molecular sieves). Their use as a precious metal support, or as a substitute for conventional silico-aluminaies. led to catalytic systems with much higher activity and selectivity in aromatic hydrocarbon conversion processes (xylene isomerization, toluene dismutation), in benzene alkylation, and even in the oxychlorination of ethane to vinyl chloride. 

The ammoxidation of toluenes substituted with electron-donating groups, for example hydroxy- and alkoxy-substituted toluenes is rather less selective. However, under carefully chosen conditions (choice of the catalyst, feed composition, reaction conditions) adequate yields of nitriles can be achieved. Stabihty of the catalyst performances is typically an issue. 

Other applications of the ammoxidation include the reactions of isobutene (—> a-methacrylonitrile), a-methylstyrene (- atropanitrile), y5-picoline nicotine nitrile and nicotinamide), toluene benzonitrile), and xylenes (—> phthalo-nitrile, terephthalonitrile, and isophthalonitrile on the way to fiber- grade diamines). 

The ammoxidation of substituted toluenes over differently prepared (NH4>2(V0)3(P207)2-and V0(P03)2-phases as well as over (VO)2P207 has been studied by catalytic and in situ-ESR measurements. For effective catalytic performance at least two structural properties were found to be essential i) Closely neighbouring centres must be exposed at the surface which enable the simultaneous adsorption and conversion of the substrate and ii) the catalyst structure must contain building blocks of exchange-coupled ions e. g. in the form of chains or layers which support the electron transport during the redox process. 

Fig. 2 Moment quotient of the ESR sngnals of various (NH4)2(V0)3(P207)2-based catalysts under ammoxidation conditions (NH3, H2O, air) in the absence ffilack bars) and in the presence of toluene (white bars)...

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