Nitrates decomposition mechanism

To darify better the role of Pt in the reduction mechanism, a physical mixture of the binary Pt/Y-Al2O3 (1 100 w/w) and Ba/Y-Al2O3 (20 100 w/w) samples was prepared and tested [117]. Also in this case NO was stored at 350 °C upon adsorption of NO in the presence of excess O2 [102], then the stability/reactivity of stored nitrates was investigated by means of TPD and H2 TPSR. The TPD data showed that decomposition of adsorbed nitrates occurs at temperatures very dose to that of adsorption the presence of H2 (TPSR run) does not decrease significantly the temperature threshold for nitrate decomposition (which is still observed near 350 °C), but instead provokes the reduction of the evolved NO to NH3 and N2. Hence the previously invoked Pt-catalyzed route is active only when Pt and Ba are dispersed over the same particle of the support. 

The vibration spectra of nitrated l,2,4-triazol-5-ones [611, 614, 615] and their energetic salts [616] are discussed. The thermal decomposition mechanism under rapid heating of thin films of 3-nitro-l,2,4-triazol-5-one was studied by pulsed infrared laser and Fourier-transform infrared spectroscopy [1071],... 

The mechanisms of n- and iso-propyl nitrate decomposition flames appear to be the same as that of the ethyl nitrate flame, the main attack on the nitrate ester being by nitrogen dioxide and nitrous acid [136]. 

Nitrates may retain water strongly and special preparative methods may be required to obtain the anhydrous salts. Residual water in nitrates and nitrites can hydrolyze the reactant on heating with the formation of basic salts and nitric acid. Studies of the radiolysis of nitrates [52-55] have provided additional information on decomposition mechanisms. 

Ammonium Nitrate. Like AP, the decomposition of AN occurs via complex decomposition mechanisms. Studies performed by Oxley and coworkers indicate two modes of decomposition.[52-54] In the temperature range 200-300 °C, decomposition starts through an endothermic dissociation to ammonia and nitric acid and the formation of the nitronium ion is the rate-determining step (See Scheme II). 

The application of the third-law method to decomposition studies [52] supported the basic assumptions underlying the physical approach to interpretation of decomposition kinetics. A good fit of e3q)eriment to theory for the ratio of the initial decomposition temperature to the E parameter, the peculiarities of carbonate decomposition in CO2 and the regularities of solid and melted nitrate decompositions are in complete agreement with the mechanism of dissociative evaporation and consumption of a part x of the condensation energy by the reactant. 

It is difficult to determine the diameter of diethyleneglycol dinitrate from experiments. Zeng et al. [3] analyzed the thermal decomposition mechanism of nitrate ether and suggested the diameter (li = 5.10 x 10 cm) of one ether, whose molecular weight is very close to diethyleneglycol dinitrate. The collision number... 

Sorescu et al. have published theoretical and computational studies of energetic salts [22]. Opinions concerning the mechanism of thermal decomposition of nitrates are approximately the same in both monographs. The decomposition mechanism of the best-known oxidizer, ammonium nitrate (AN), is given below. In the solid state, AN is dissociated according to the following equilibrium [ 11,22] ... 

Poly(azophenylene-o-carborane) (see 6) has been prepared from diphenyl-o-carborane by means of nitration, reduction, and acylation to initially give 1,2-bis(/ -nitroso-acetylaminophenyl)-o-carborane (NAFC). Rapid decomposition in solution affords phenylene amino phenyl carborane (PAFC) by recombination of phenylene and azophenylene radicals.40 These radicals have also been utilized to form copolymers of carborane-containing copolymers from monomers polymerizable via radical mechanisms. Thus, copolymers of polystyrene and poly(azophenylene) can be readily formed by means of emulsion copolymerization of styrene with NAFC decomposition products. 

Above 140°C its exothermic decomposition to metal and carbon dioxide readily becomes explosive [1], A 1 kg batch which had been thoroughly dried at 50°C exploded violently when mechanical grinding in an end-runner mill was attempted [2], Explosions have been experienced when drying the oxalate as low as 80°C [6], It is a compound of zero oxygen balance. The explosion temperature of the pure oxalate is lowered appreciably (from 143 to 122°C) by application of an electric field [3], The salt prepared from silver nitrate with excess of sodium oxalate is much less stable than that from excess nitrate [4], Decomposition at 125°C in glycerol prevents explosion in the preparation of silver powder [5],... 

Malecki A., Gajerski R., Labus S., Prochowska-Klisch B., and Wojciechowski K.T. 2000. Mechanism of thermal decomposition of d-metals nitrates hydrates. J. Therm. Anal. Calorim. 60 17-23. 

Fig. 9.1. Simplified reaction mechanisms in the hydrolytic decomposition of organic nitrates. Pathway a Solvolytic reaction (Reaction a) with formation of a carbonium ion, which subsequently undergoes SN1 addition of a nucleophile (e.g., HO ) (Reaction b) or proton E1 elimination to form an olefin (Reaction c). Pathway b HO -catalyzed hydrolysis (,SN2). Pathway c The bimolecular carbonyl-elimination reaction, as catalyzed by a strong base (e.g., HO or RO ), which forms a carbonyl derivative and nitrite.

There are a number of reaction mechanisms by which nitrates can undergo hydrolytic decomposition, as summarized in simplified form in Fig. 9.1 [23], Pathway a is the unimolecular solvolytic route, which forms nitrate and a carbonium ion (Pathway a, Reaction a). The latter can add a nucleophile,... 

On the basis of these data, the following mechanism for reduction by hydrogen can be suggested. H2, activated over the Pt sites according to the Pt-catalyzed pathway discussed previously, reduces the stored nitrates directly to ammonia or, more likely, induces the decomposition of nitrates to gaseous NO, which are then reduced by H2 to NH3 over the Pt sites [overall reaction (13.47)]. Once ammonia has been formed, it can react with adsorbed nitrates and this reaction is very selective towards nitrogen. It is worth noting that the reaction of ammonia with NOx obeys the stoichiometry of reaction (13.49), which is different from that of the well-known NH3-NO SCR reaction because it implies the participation of nitrates. 

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