Benzene to Phenol with

It was reported independently by three research groups that MFI-type zeolites selectively catalyze the reaction of N20 with benzene to give phenol C6H6 + N20 — C6H5OH + N2 [93-96]. Fe/ZSM-5 shows remarkable performance in benzene hydroxylation to phenol with N20 as oxidant, which is the first example of a successful gas phase direct phenol synthesis from benzene [97]. No other catalysts show similar high performances to the Fe/ZSM-5 catalyst. At present, iron is the sole element capable of catalyzing the benzene-to-phenol reaction [98]. Direct oxidation of benzene to phenol by N20 has been commercialized in the so-called AlphOx process in Solutia Inc., US A, where N20 is obtained as a by-product in adipic acid production with nitric acid [97, 99, 100] a selectivity 95% to phenol is achieved at 40% conversion at around 4000 C. But the process is cost-effective only if N20 can be obtained cheaply as a by-product in adipic acid production. 

Considerable efforts have been made to understand ZSM-5-based catalysts for the selective oxidation of benzene to phenol by nitrous oxide. However, the nature of the active species remains unclear. The most important proposals for the active species are extraframework Fe species [101], Bronsted add sites [102] and Lewis and A1 sites [103, 104]. The activity is usually interpreted in terms of very small, possibly 

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Scheme 21 Hydroxylation of benzene to phenol with nonheme iron complex 35 [142]...

Hensen EJM, Zhu Q, van Santen RA. 2005. Selective oxidation of benzene to phenol with nitrous oxide over MFI zeolites. 2. On the effect of the iron and aluminum content and the preparation route. J Catal 233 136-146. 

Another example of heterogeneous catalysis by oxo-ions is the one-step oxidation of benzene to phenol with nitrous oxide, N2O. Fe/MFI catalysts have, again been found to be very active. This catalysis was discovered by Iwamoto and has been extensively studied by the group of G. Panov in Novosibirsk. " Preparations of Fe/MFI which appear highly active for this reaction display poor activity for NOj reduction and those which are optimum for that process, are poor for benzene oxidation. This shows that different sites are used. Work by Jia et al. revealed that the active sites for benzene oxidation appear to be Fe-oxo-ions containing only one Fe ion. This does not necessarily mean that the sites are mononuclear. A recent work by Zhu et al. has rather suggested that the site consists of one Fe and one Al + ion, the latter ion having left the zeolite framework. ... 

J. Jia, K. S. Pillai, and W. M. H. Sachtler, One-step oxidation of benzene to phenol with nitrous... 

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. 

The same authors reported the liquid-phase oxidation of benzene to phenol, with O2 as the oxidant and Cu-zeolite or Cu-MCM as the catalyst (175, 176). However, phenol yields were low, a large amount of supported Cu was required, and ascorbic acid was used as a stoichiometric coreductant. Phenol production was accompanied by the formation of H2O2 in solution ... 

The oxidation of benzene to phenol can also be achieved using nitrous oxide as an oxidant in the presence of a catalytic system such as vanadium, molybdenum or tungsten oxides at 550 °C, and after addition of 30% of water to afford phenol in 10% yield . More effective catalytic systems have been investigated and zeolites show promise to be good catalysts for the oxidation of benzene to phenol with nitrous oxide . The use of zeolite catalysts has led to a reduction in the reaction temperature to 300-400°C, to the exclusion of water addition to the reaction mixture and to an increase in the yields up to 25-30% . Recently, direct oxidation of benzene to phenol by nitrous oxide has been commercialized . 

Direct Oxidation of Benzene to Phenol with Hydrogen Peroxide... 

Balducci, L., Bianchi, D., Bortolo, R., D Aloisio, R., Ricci, M., Tassinari, R. and Ungarelli, R. (2003) Direct oxidation of benzene to phenol with hydrogen peroxide over a modified titanium silicalite. Angew. Chem. Int. Ed., 115, 5087-5090. 

Characteristic features of vanadium containing heteropoly catalysts for the selective oxidation of hydrocarbons have been described. MAA yield ftom isobutyric acid was successfully enhanced by the stabilization of the vanadium-substituted heteropolyanions by forming cesium salts. As for lower alkane oxidation by using vanadium containing heteropoly catalysts, it was found that the surface of (V0)2P207 was reversibly oxidized to the Xi (8) phase under the reaction conditions of n-butane oxidation. The catalytic properties of cesium salts of 12-heteropolyacids were controlled by the substitution with vanadium, the Cs salt formation, and the addition of transition metal ions. By this way, the yield of MAA from isobutane reached 9.0%. Furthermore, vanadium-substituted 12-molybdates in solution showed 93% conversion on H2O2 basis in hydroxylation of benzene to phenol with 100% selectivity on benzene basis. 

The 0 rigin o f t he c atalytic a ctivity i n t he v arious r eactions c atalyzed b y F e-zeolites h as been intensively debated over the last decade. In spite of the considerable efforts to characterize these materials, available data are not yet sufficient to conclude exclusively on the structure of the active iron. Binuclear iron species in FeZSM-5 have been designated as the active site in various reactions, including direct N2O decomposition, selective oxidation of benzene to phenol with N2O, and selective catalytic reduction (SCR) of NO c with hydrocarbons. However, in the last reaction, small oligonuclear species of composition Fc404 and isolated iron ions have also been proposed as active sites. ... 

Copper(I) chloride promotes the oxidation of benzene to phenols with molecular oxygen [37a], The active species is proposed to be a hydroxyl radical generated in the following manner ... 

A high selectivity of iron-containing ZSM-5 has been demonstrated for the direct oxidation of benzene to phenol with N2O as the oxidant (which can be obtained from the waste streams of other processes). 

Fe-MFI is among the reported (209) catalysts for the oxidation of benzene to phenol with reactants in the gas phase. At a benzene... 

The single-step oxidation of benzene to phenol without coproduct formation is a great industrial challenge. Currently, phenol is produced by the Cumene process, which also yields stoichiometric amounts of acetone. However, there are recent developments in the oxidation of benzene to phenol with aqueous hydroperoxides as oxidants, TS-1 as the catalyst, and sulfolane (thiophene, tetrahydro, 1,1-dioxide) as a cosolvent (204b). 

Figure 1.17 Reaction steps, reaction conditions, and typical results for the direct hydroxylation of benzene to phenol with modified Fe-ZSM-5 as the catalyst and NjO as the oxidizing agent according to the Solutia process. Adapted from Chemical Engineering, September 2004, p. i, with permission from Chemical Engineering.

Niwa S., Eswaramoorthy M., Jalajakumari N., Anuj R., Naotsugu L, Hiroshi S., Takemi N., Fuji M. 2002. A one-step conversion of benzene to phenol with a palladium membrane. Science 295 105-107. 

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