N2O oxidation

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

In order to understand the reason for such a beneficial N2O oxidizing effect, a detailed mechanism of its decomposition as a stage supplying oxygen to the surface has been studied [4,12]. This study revealed a special type of iron active sites in ZSM-5 matrix (called a-sites), which decompose N2O producing a new oxygen form (a-form) ... 

Divalent Metal Molybdates. Except for the first point, the conversion of ethane did not change in the conditioning period at 823 K and it lay in the same range as for the N2O as oxidant. The main product was ethylene the selectivity of its foimation mai kedly exceeded that obtained with N2O as oxidant. Acetaldehyde was formed with 4.8% and 6.8% selectivity on the Mg and Zn salts. As a result, the yields for ethylene and acetaldehyde were much higher than in the case of N2O oxidation (Figure 5). Other hydrocarbons and alcohols were also detected in very small concentrations, with less than 1% selectivity. 

The synthesis and chemistry of platinum nitrates has been recently reviewed.1621 The only homoleptic nitrate complex is K2Pt(N03)6 formed from K tBre and N2Os. Oxidation of the nitrito complex K2Pt(N02)4 gives K2Pt(N02)6> and not the nitrate complex. 

K. Yoshizawa, Y. Shiota, T. Yumura and T. Yamabe, J. Phys. Chem. B, 104, 734 (2000) Chem. Eng. News, April 6, 21 (1998). See also the recent experimental work on the Fe-silicahte catalyst for the N2O oxidation of benzene to phenol R. Leanza, I. Rossetti,... 

The most widely used process of the high temperature growth of Si02 by LPCVD involves the N2O oxidation of SiCl2H2 (Eq. 5.14). 

Nitrous oxide is non-explosive itself, but can form flammable mixtures with organic compounds. This should be taken into account for providing a safe working environment when using N2O oxidant. Table 7.2 gives the flammability limits of some compounds in mixtures with N2O. These data are quite scarce and reported... 

A specificity of N2O oxidant compared to O2 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 N2O leads to selective formation of phenol, while O2 leads only to the products of complete oxidation. 

Recently, some other oxidation reactions using N2O oxidant such as the ammoxida-tion and epoxidation were successfully conducted. The ammoxidation of propane proceeds with rather high selectivity over FeZSM-5 zeolite [151]. Remarkably, the reaction most effectively proceeds in the presence of a N2O-O2 mixture. 

In 2002, this type of N2O oxidation was re-discovered by Panov et al. [168]. Being guided by quite a different idea, the authors [168] used milder conditions and obtained much better selectivity, which in many cases exceeded 90%. Such a high selectivity was shown to relate to a non-radical type reaction mechanism as well as to a remarkable feature of the oxidant. N2O reacts solely with alkene C=C bonds and is inert towards all other bonds. Therefore, reaction products having no double bonds are not subjected to overoxidation. Only non-oxidation side processes may be a reason for decreasing selectivity. 

Table 9 Values for the N NMR chemical shift of dinitrogen states [166] relative to gaseous N2O oxide in various adsorption...

Dinitrogen oxide, nitrous oxide, N2O. Colourless gas, m.p. —9T C, b.p. —88-5°C (heat on NH4NO3). Decomposes to N2 and O2 above SOO C can be detonated. Linear molecule NNO. Used as a mild anaesthetic. 

Admixtures of oxygen or oxidizing agents such as N2O to the silane plasma enable the deposition of Si02 films. Other Si-containing compounds such as SiCl or tetraethoxysilane (Si(OCH2CH2)4) are used for plasma-enlranced Si02 deposition at lower temperatures [33],... 

Although many variations of the cyclohexane oxidation step have been developed or evaluated, technology for conversion of the intermediate ketone—alcohol mixture to adipic acid is fundamentally the same as originally developed by Du Pont in the early 1940s (98,99). This step is accomplished by oxidation with 40—60% nitric acid in the presence of copper and vanadium catalysts. The reaction proceeds at high rate, and is quite exothermic. Yield of adipic acid is 92—96%, the major by-products being the shorter chain dicarboxytic acids, glutaric and succinic acids,and CO2. Nitric acid is reduced to a combination of NO2, NO, N2O, and N2. Since essentially all commercial adipic acid production arises from nitric acid oxidation, the trace impurities patterns ate similar in the products of most manufacturers. 

Other Methods. A variety of other methods have been studied, including phenol hydroxylation by N2O with HZSM-5 as catalyst (69), selective access to resorcinol from 5-methyloxohexanoate in the presence of Pd/C (70), cyclotrimerization of carbon monoxide and ethylene to form hydroquinone in the presence of rhodium catalysts (71), the electrochemical oxidation of benzene to hydroquinone and -benzoquinone (72), the air oxidation of phenol to catechol in the presence of a stoichiometric CuCl and Cu(0) catalyst (73), and the isomerization of dihydroxybenzenes on HZSM-5 catalysts (74). 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

A smaller factor in ozone depletion is the rising levels of N2O in the atmosphere from combustion and the use of nitrogen-rich fertilizers, since they ate the sources of NO in the stratosphere that can destroy ozone catalyticaHy. Another concern in the depletion of ozone layer, under study by the National Aeronautics and Space Administration (NASA), is a proposed fleet of supersonic aircraft that can inject additional nitrogen oxides, as weU as sulfur dioxide and moisture, into the stratosphere via their exhaust gases (155). Although sulfate aerosols can suppress the amount of nitrogen oxides in the stratosphere... 

Exceptions are salts of oxidizing anions, which decompose with oxidation of the ammonium ion to nitrous oxide [10024-97-2], N2O, or nitrogen, N2. 

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