Zeolite nitrous oxide

Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium, platinum, palladium, or irridium. The oxidizing agent is nitrous oxide, which is unavoidable a byproduct from the oxidation of KA oil (see KA oil, this chapter) to adipic acid using nitric acid as the oxidant. 

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

AROMATICS HYDROXYLATION WITH NITROUS OXIDE 2.1. Discovering zeolite catalysts... 

In the 1980 s zeolites attracted a renewed attention. They were shown to be rather promising catalysts if, instead of O2, a chemically pre-modified oxygen entering the oxygen-containing molecules is used. The most known example is an excellent catalytic performance of titanium silicalites in the liquid phase oxidations with H2O2 [5]. A gas phase oxidation with nitrous oxide is another approach in this field being intensively developed in the last years [2],... 

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. 

Despite several decades of studies devoted to the characterization of Fe-ZSM-5 zeolite materials, the nature of the active sites in N20 direct decomposition (Fe species nuclearity, coordination, etc.) is still a matter of debate [1], The difficulty in understanding the Fe-ZSM-5 reactivity justifies a quantum chemical approach. Apart from mononuclear models which have been extensively investigated [2-5], there are very few results on binuclear iron sites in Fe-ZSM-5 [6-8], These DFT studies are essentially devoted to the investigation of oxygen-bridged binuclear iron structures [Fe-0-Fe]2+, while [FeII(p-0)(p-0H)FeII]+ di-iron core species have been proposed to be the active species from spectroscopic results [9]. We thus performed DFT based calculations to study the reactivity of these species exchanged in ZSM-5 zeolite and considered the whole nitrous oxide catalytic decomposition cycle [10],... 

Figure 2. Energy versus reaction coordinate for the dissociation of the first nitrous oxide over i) Z " Fe, (p-t))(p-OI I)Fe211 and ii) Z " Qh [Fe1( t-0)( t-0H)Fe2]+. For clarity sake, the clusters representing part of the zeolite were omitted in these figures. N20 molecule is represented by a red ball (O) and two bleu balls (N).

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. ... 

Fluorobenzene is hydroxylated in 90% yield with nitrous oxide (N,0) over a zeolite catalyst, but a mixture of regioisomers is formed (Table 7).1091,2,4,5-Tetrafluorobenzene is oxidized, instead of nitrated, by fuming nitrie acid to 2,5-difluoro-l,4-bcnzoquinone (1) in low yield.1,0... 

A statistical thermodynamic equation for gas adsorption on synthetic zeolites is derived using solid solution theory. Both adsorbate-adsorbate and adsorbate-adsorbent interactions are calculated and used as parameters in the equation. Adsorption isotherms are calculated for argon, nitrogen, ammonia, and nitrous oxide. The solution equation appears valid for a wide range of gas adsorption on zeolites. 

The reduced iron atoms of complex C, being inert to dioxygen, are readily oxidized by nitrous oxide into complex D to give adsorbed species of a-oxygen, Oa. As Figure 7.3 shows, the reversible redox transition Fc" <-> Fe provides the catalytic activity of FeZSM-5 both the oxidation cycle due to the oxygen transfer from N20 to a substrate and the decomposition cycle of N20 into N2 and 02 due to recombination of a-oxygen into the gas phase. The decomposition is an environmentally important process, and FeZSM-5 zeolites are considered to be the best catalysts for this reaction (see review [117] and references therein). 

A specificity of N20 oxidant compared to 02 is one of the most interesting points arising from benzene oxidation over FeZSM-5 zeolites. The specificity is clearly seen from the results presented in Table 7.6 [ 118]. With nitrous oxide, benzene conversion is 27% at 623 K, whereas with dioxygen it is only 0.3% at 773 K. Moreover, the reaction route changes totally N20 leads to selective formation of phenol, while 02 leads only to the products of complete oxidation. 

Although the epoxidation by nitrous oxide proceeds over non-zeolite catalysts, they also include iron as an active element One may think that in all these cases a special oxygen species generated by N20 plays an important role, similar to the a-oxygen on FeZSM-5. 

Nitrous oxide offers a tempting possibility for the epoxidation of propylene and butylene in the gas phase. Encouraging results were obtained with Fe-modified Si02 and some zeolite-like catalysts. No other oxidant allows selective performance of these delicate reactions. 

The H-ZSM-5 coatings were tested for the one-step oxidation of benzene by nitrous oxide to phenol. The grids had a total area of 9 cm2, a wire diameter of 250 pm and a mesh size of 800 pm. Fifteen grids formed a stack separated by steel rings. By acid pretreatment of the grids, defects were generated which are known to become crystallization centers during the synthesis of the zeolite. 

It was shown (Ovanesyan et al., 2000) that iron complexes formed during the thermal treatment of FeZSM-5 zeolite perform single-turnover cycles of methane oxidation to methanol at ambient conditions when nitrous oxide is used as a source of oxygen. The long-living active intermediate is capable of transferring an accepted O atom into a C-H bond of methane to produce methanol at 100% selectivity. On the basis of joint Mossbauer and catalytic data, the structure and composition of iron active centers are suggested. 

AlphOx A process for oxidizing benzene to phenol, using nitrous oxide as the oxidant and a zeolite catalyst. Developed by the Boreskov Institute of Catalysis and Solutia, and proposed to be commercialized in Pensacola, FL, in 2003 however, this plan was subsequently abandoned. In 2004 the process was relaunched by GTC Technology Inc. and Solutia, following extensive testing by Solutia in Pensacola. 

Closer to industrial application however, is the gas phase hydroxylation with nitrous oxide as the oxidant (Equation 39). The reaction is carried out at 350°C with a selectivity to phenol of 98%, at 27% benzene conversion. The catalyst is Fe-ZSM-5 a zeolite containing A1 and Fe in the silicalite-1 framework. Active sites are thought to be binuclear clusters of iron oxide, formed in the channels by the migration of Fe, during thermal treatments of the zeolite. Selectivity is of... 

Sorption thermodynamic functions of nitrous oxide, N2O, are described for zeolites NaLSX and CaLSX in shapes cA clay-bound beads. They were determined by the Sorption Isosteric Method (SIM) over complete ranges of sorption-phase concentration and compared with those for carbon dioxide, C(>2. nepo earlier for the same NaLSX sorbent... 

Modified high-silica zeolites are used for selective oxidation of mono- and difluorobenzenes into corresponding fluorophenols using nitrous oxide as an oxidant. The nature of the active sites and the reaction mechanism are discussed. 

In this paper, we have investigated the oxidation of fluorobenzenes on the modified HZSM-5 zeolites using nitrous oxide as an oxidizing agent. 

We used HZSM-5 zeolites (Si02/AI203 = 40 - 120) and H[Ga]ZSM-5 zeolites (Si02/AI203 = 60) prepared by decationization of the Na-form with a 1 N aqueous solution of HCI. The preliminary activation of all catalyst samples was carried out at temperatures of 820 - 1120 K either in an Ar flow or in an air flow for 6 h. For comparison, we prepared the HZSM-5 zeolite modified by 2 wt % Cu (wet impregnation with a 1 M nitrate solution with further nitrate decomposition at 820 K in air) and tested this sample in the fluorobenzene oxidation by nitrous oxide. 

We studied the oxidation of fluorobenzene with nitrous oxide under the same conditions as reported in [8, 11]. Oxidation of monofluorobenzene on the HZSM-5 zeolite modified in such a way that strong Lewis acidity is induced in the sample... 

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 . 

The various processes for the catalytic reaction are similar. The factor that makes the difference is the choice of catalyst, which in turn affects the temperature regime needed to trigger the decomposition of nitrous oxide. In the literature, numerous works illustrate the several classes of catalysts appropriate for this reaction [9a, k] noble metals (Pt, Au), pure or mixed metal oxides (spinels, perovskite-types, oxides from hydrotalcites), supported systems (metal or metal oxides on alumina, silica, zirconia) and zeolites. 

The selective insertion of an oxygen atom into a benzene carbon-hydrogen bond to yield phenol is not a classical organic chemistry reaction. The first process for such a reactions was the Solutia process, based on discoveries by Panov and coworkers at the Boreskov Institute of Catalysis in Novosibirsk and then developed in close cooperation with Monsanto. In this process, the oxidant is nitrous oxide, N2O, while an iron-containing zeolite is used as the catalyst (Equation 13.4) ... 

Figure 13.3 shows a plant layout. Recycled benzene along with makeup benzene and nitrous oxide are preheated and continuously fed to a moving bed reactor utilizing the zeolite catalyst. The latter flows vertically down the reactor by gravity, while the reaction gas flows across the annular catalyst beds. The predominant reactions are exothermic about 250 kj are released per mole of phenol produced. In addition, significantly more heat can be generated by the deep oxidation of benzene to... 

ZSM5 type zeolites were used as catalysts for the one-step synthesis of phenol hy benzene partial oxidation with nitrous oxide. Isomorphous substitution of Al ions by other trivalent metal ions revealed a high catalytic performance of the H-Ga-ZSM5 in a wide temperature range. Systematic variation of the partial pressures of the reactants led to satisfactory preliminary kinetic models. Deactivation could be reduced by postsynthetic catalyst silylation which is believed to block the strongest acid sites responsible for coke formation. 

With worldwide phenol consumption exceeding 5 million tons in 1995, optimizing production routes of this essential chemical becomes very important. As an alternative to the traditional cumene process, a one-step-synthesis of phenol from benzene is highly desirable. With a ZSM5 type zeolite in its acid form as catalyst and nitrous oxide as oxidant, benzene may be directly oxidized to phenol [1-4] ... 

The main problems of this new route to phenol are the high costs of nitrous oxide and the strong deactivation of zeolite catalysts due to coke formation. Nevertheless less expensive nitrous oxide may be recovered from the waste gas stream of adipic acid plants, attempts to reduce deactivation by a modification of the zeolite catalysts appear promising. 

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