Nitrous oxide decomposition reaction mechanism

One of the few cases in which hydrogenated surface complexes have been suggested to be active involves the decomposition of nitrous oxide.The reaction was suggested to involve hydrogen in the carbon, although the reaction mechanism was written in terms of gas phase hydrogen involved in a free radical chain reaction. As a result, the importance of hydrogenated complexes is open to question. 

Mechanism of the Epoxidation Reaction - Involvement of Adsorbed Oxygen Species. Herzog has reported that the use of nitrous oxide rather than oxygen as the oxidant for ethylene epoxidation results in a considerably reduced selectivity. Since nitrous oxide decomposition leads primarily to adsorbed atomic oxygen, Herzog concluded that molecular oxygen species are required for the partial oxidation reaction. More recently this experiment has been repeated in a closed recirculatory system the same result was obtained. When the reaction was carried out in the presence of both 02 and N2 0 the ethylene oxide contained 0 exclusively while was incorporated into the carbon dioxide. 

Theories of catalysis (2-5) would associate the activity with certain electronic and geometric attributes of the catalyst which are fundamental to our understanding of reaction mechanisms. The electronic mechanism for the heterogeneous dehydrogenation of hydrocarbons has been postulated by Weyl (6) to be similar to that of nitrous oxide decomposition. To clarify the electronic mechanism of re-forming reactions, the decomposition of nitrous oxide was studied. 

Hansen N, Heyden A, BeU AT, KeU FJ (2007) A reaction mechanism for the nitrous oxide decomposition on binuclear oxygen bridged iron sites in Fe-ZSM-5. J Phys Chem C 111 2092... 

The decomposition of nitrous oxide over various metal oxides has been widely investigated by many investigators (1-3). Dell, Stone and Tiley (4) have compared the reactivity of metal oxides and shown that in general p-type oxides were the best catalysts and n-type the worst, with insulators occupying an intermediate position. It has been generally accepted (5) that this correlation indicates that the electronic structure of the catalyst is an important factor in the mechanism of the decomposition of nitrous oxide over metal oxides catalysts. The reaction is usually written (4) as... 

Nitrosyidisulfonic acid, reaction mechanisms, 22 129, 130 Nitrous acid, 33 103 decomposition, rate constants, 22 157 as oxidizing agent, 22 133 reaction mechanisms, 22 143-156 electrophilic nitrosations, 22 144-152 with inorganic species, 22 148, 149 nitrite oxidation by metals, 22 152-154 oxidation by halogens, 22 154, 155 in solution, 22 143, 144 reduction by metals, 22 155, 156 Nitrous oxide reductase, 40 368 Nitroxyl, reaction mechanisms, 22 138 Nitrozation, pentaamminecobalt(III) complexes, 34 181... 

It is probable that the actual mechanism of the decomposition is unimolecular, but, the observed order of the reaction being zero, we cannot tell whether the molecules decompose singly or by interaction with their neighbours. The catalytic decomposition of hydrogen iodide on the surface of platinum can actually be shown to be unimolecular. The heat of activation in this instance is even lower (14,000 cals.), but is again subject to the same uncertainty as the values for the unimolecular reactions of nitrous oxide. 

The ability of nitrous oxide to forma 1,3-dipole (Section 7.2) seems to be of critical importance for the reaction with alkenes. The oxygen transfer proceeds via the 1,3-dipolar cycloaddition mechanism, assuming intermediate formation of a 1,2,3-oxadiazoline complex, the decomposition of which leads to a carbonyl compound ... 

The majority of the data seem to favor the hypothesis that in complex molecules the energy must become localized in a particular valence bond before reaction can take place. This seems to be a reasonable assumption, and furthermore, it offers a mechanism for the time-lag which is necessary between activation and decomposition. We saw that this was particularly true of the complex molecules, and, as a matter of fact, the simple molecules such as nitrous oxide are so small that there is no chance for special localization of energy. 

The first-order reaction rate constant for the isomerization of peroxynitrous acid to nitrate is 4.5 s 1 at 37°C therefore, at pH 7.4 and at 37°C the half-life of the peroxynitrite/peroxynitrous acid couple (let both these species be referred to as peroxynitrite for the sake of brevity) is less than 1 s. The reaction mechanism of peroxynitrite decomposition was a subject of controversy. Primarily proposed was that peroxynitrous acid decomposes by homolysis, producing two strong oxidants hydroxyl radical and nitrous dioxide (B15) ... 

PlOC-3 See The decomposition of nitrous oxide on neodymium oxide, dysprosium oxide and erbium oxide, J. Catal., 28, 428 (1973). Some investigators have reported the rate of this reaction to be independent of oxygen concentration and first-order in nitrous oxide concentration, while others have reported the reaction to be first-order in nitrous oxide concentration and negative one-half-order in oxygen concentration. Can you propose a mechanism that is consistent with both observations ... 

More generally, if this structural modification is a common phenomenon, it is liable to occur during all catalytic reactions, even at moderate temperatures, at the surface of catalysts which have not been sintered at high temperatures. A study of the mechanism of decomposition of nitrous oxide at 250° on a divided nickel oxide [NiO(250°)J, during successive runs, is particularly interesting in this respect. 

Since the initial rate of decomposition on the surface of a freshly prepared sample of NiO(250°) does not depend upon the initial pressure of nitrous oxide (Table XVIII), the first step of the reaction mechanism is the adsorption of nitrous oxide in an ionic form, as shown by conductivity measurements (55). 

Regardless of the particular mechanism, if the activation process is accomplished through the absorption of single or multiple frequencies, then a marked increase in the radiation density of these frequencies should cause a change in reaction velocity. The decomposition of ozone and nitrous oxide have been studied from this point of view and are reported here. Since the inception of this work, it has been found elsewhere3 that the oxidation of alcohol vapor and the decomposition of nitrogen pentoxide and hydrochloric acid were not affected by infra-red radiation. The present work confirms these results for two additional reactions. 

Summary.—The mechanism of the activation process in gaseous systems has been investigated from the point of view of (1) activation by radiation (2) activation by collision. An increase in the radiation density of possible activating frequencies has resulted in no increased reaction velocity. The study of the bimolecular decomposition of nitrous oxide at low pressures has led to the conclusion that the reaction is entirely heterogeneous at these pressures. A study of the unimolecular decomposition of nitrogen pentoxide between pressures of 7io mm. Hg and 2 X 10 3 mm. Hg shows no alteration in the rate of reaction such as was found by Hirst and Rideal but follows exactly the rate determined by Daniels and Johnson at high pressures. No diminution of the reaction velocity as might be ex-expected from Lindemann s theory was observed. 

The kinetics of the reaction between peroxomonosulphate and thiocyanate were earlier interpreted in terms of the intermediate of species such as HS(0)CN, (SCN)a, and HO(SO)CN. No definite proof of this is available, but the detection of similar intermediates, RSO2CN and R(SO)CN, in reactions between alkyl thiocyanates and peroxomonosulphate lends support to the intermediacy of HS(0)CN and HO(SO)CN in the peroxomonosulphate-thiocyanate reaction.The kinetics of decomposition of the iV-nitroso-hydroxylamine-A -sulphonate anion to sulphate and nitrous oxide have already been described under nitrogen. The mechanism of substitution at sulphur(iv) in sulphinyl compounds, RS(0)Y, is still a topic of unresolved discussion, despite much effort in this area. The question awaiting answer is whether the mechanism is simple Ssl or whether there is a four-co-ordinate intermediate of significant lifetime. > Though the determination of Bronsted coefficients did not provide definite mechanistic evidence relating to substitution at... 

We introduce at this point a simple example mechanism that will be used in Sections 4 and 6 to illustrate important features of combustion mechanisms. Suppose that nitrous oxide N2O is heated rapidly to 1500 K at atmospheric pressure, whereupon it decomposes in an exothermic reaction. The species that one might assume to be present as the decomposition proceeds are to include N2O itself, N2,02, NO, NO2, N2O4, and O atoms, a total of = 7 species. Suppose that the forward and reverse directions of the following eight reactions are to be tested as a possible reaction mechanism ... 

Many reactions which formally involve nitrites in acidic solutions or in presence of a number of buffers turn out to have mechanisms in which the nitrogen oxides are dominant species. These reactions are to be discussed elsewhere and include the decomposition of nitrous acid and its reverse , and of its reaction with arsenious acid ... 

The sum of S11-S14 yields the overall NO oxidation reaction (R5). The proposed mechanism involves the oxidation of NO by ferric hydroxide (Fe -OH), producing HONO. The production of the Fe nitrite surface species (Fe -ONO) subsequently occurs by the reaction of nitrous acid with additional Fe -OH. The latter species has been shown to be thermally stable under UHV conditions at temperatures up to ca. 400 °C [70]. Decomposition of the nitrite results in reduction to Fe and yields NO2. Reoxidation of Fe " occurs with molecular oxygen in S14. The proposed mechanism considers that the decomposition step S13 is the rate-determining step, so steps Sll, S12, and S14 are equilibrated and the concentration of nitrous acid and other species is determined by the equilibrium of steps Sll and SI2. In essence, the Redox model requires the formation of nitrite for NO2 to be generated. 

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