Ammonia, formation from nitrate

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Many of the reactions producing imidazoles in tobacco and tobacco smoke involve the interaction of carbohydrates with ammonia, which has several precursors in tobacco. Amino acids and proteins can contribute to the formation of smoke amines and the formation of ammonia. Johnson et al. (1964) conclusively demonstrated through experiments with W-glycine that it is an ammonia source. In addition to amino acids, nitrates have been shown to be efficiently converted during the smoking of a cigarette to ammonia (1964). This ammonia from nitrates was shown to participate in the formation of many nitrogenous compounds in smoke. Thus, leaf nitrates as well as amino acids and proteins are considered the major sources of ammonia in tobacco smoke. 

Clayton et al. [22] also suggested that the ammonia formation mechanism includes the activation of H2 on Pt sites. They proposed that adsorbed nitrates are decomposed into NOx and released in the gas phase, due to hydrogen spill-over from the noble metal to the alumina support. NOx species are readily reduced to ammonia due to high local H/N ratio. 

Qualitative. The classic method for the quaUtative determination of silver ia solution is precipitation as silver chloride with dilute nitric acid and chloride ion. The silver chloride can be differentiated from lead or mercurous chlorides, which also may precipitate, by the fact that lead chloride is soluble ia hot water but not ia ammonium hydroxide, whereas mercurous chloride turns black ia ammonium hydroxide. Silver chloride dissolves ia ammonium hydroxide because of the formation of soluble silver—ammonia complexes. A number of selective spot tests (24) iaclude reactions with /)-dimethy1amino-henz1idenerhodanine, ceric ammonium nitrate, or bromopyrogaHol red [16574-43-9]. Silver is detected by x-ray fluorescence and arc-emission spectrometry. Two sensitive arc-emission lines for silver occur at 328.1 and 338.3 nm. 

With such a diversity of N-nItrosatlon pathways theoretically possible. It Is comforting to note that only a few combinations of circumstances have been Implicated In environmental nitrosamlne formation thus far. Two of these are so facile and prevalent that, as of 20 years ago, they were the only recognized mechanisms of N-nItrosatlon. They Involve the Interaction of di-or trisubstituted ammonia derivatives with a nitrite Ion, as Illustrated In Figure 1 for the secondary amines, under the catalytic Influence of acid. Note the Important special cases of nucleophilic displacement of water from the nitrous acldlum Ion, H20-N0 , by a second nitrite Ion to yield NoOo (as in the reaction at the top of Figure 1), and by nitrate (bottom of Figure... 

Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium precursors (acetate, chloride, nitrate, sulphate and ammonium dichromate) were studied in the selective ammoxidation of ethylene to acetonitrile. Cr-ZSM-5 catalysts were characterized by chemical analysis, X-ray powder diffraction, FTIR (1500-400 cm 1), N2 physisorption (BET), 27A1 MAS NMR, UV-Visible spectroscopy, NH3-TPD and H2-TPR. For all samples, UV-Visible spectroscopy and H2-TPR results confirmed that both Cr(VI) ions and Cr(III) oxide coexist. TPD of ammonia showed that from the chromium incorporation, it results strong Lewis acid sites formation at the detriment of the initial Bronsted acid sites. The catalyst issued from chromium chloride showed higher activity and selectivity toward acetonitrile. This activity can be assigned to the nature of chromium species formed using this precursor. In general, C r6+ species seem to play a key role in the ammoxidation reaction but Cr203 oxide enhances the deep oxidation. 

It appears that nitrates can be reduced by H 2 already at very low temperatures (from 60 °C), leading to the formation of ammonia and of minor amounts of N2 (Figure 13.18a). The overall H2 consumption is in line with the stoichiometry of the following reactions leading to the formation of NH3 and N2 ... 

The results ofNH3 TPSR experiment (Figure 13.18b) show that ammonia reduces the stored nitrates starting from 150 °C with formation of nitrogen according to the follovrtng overall stoichiometry ... 

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