Ammonia oxidation chemistry

Notably, all commercial nitric acid production methods used today are centred around the oxidation of ammonia. It is therefore appropriate to investigate the chemistry of this process, in the knowledge that it is directly applicable to any of the production 

The chemistry of the oxidation of ammonia is surprisingly simple. It begins with a single pure compound, plus air and water, and ends 

The first step in the process is the heterogeneous, highly exothermic, gas-phase catalytic reaction of ammonia with oxygen (Reaction 2). The primary oxidation of ammonia to nitric acid (over a catalyst gauze of 9 l platinum/rhodium alloy) proceeds rapidly at process temperatures between 900-970°C. 

The second step in the process involves two reactions (Reactions 3 and 4). These are the oxidations of nitrogen monoxide to the dioxide and tetroxide forms. The equilibrium mixture is loosely referred to as nitrogen peroxide. Both reactions are homogenous, moderately exothermic, gas-phase catalytic reactions. 

All reactions shown are highly exothermic. The known side reactions and their heats of reaction are presented in Appendix A (Table A.2). The source of this reaction data is Ref. PT1 (p.174). 

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I 1.2.2. Nitric Acid by Ammonia Oxidation Chemistry and Theory... 

Toray. The photonitrosation of cyclohexane or PNC process results in the direct conversion of cyclohexane to cyclohexanone oxime hydrochloride by reaction with nitrosyl chloride in the presence of uv light (15) (see Photochemical technology). Beckmann rearrangement of the cyclohexanone oxime hydrochloride in oleum results in the evolution of HCl, which is recycled to form NOCl by reaction with nitrosylsulfuric acid. The latter is produced by conventional absorption of NO from ammonia oxidation in oleum. Neutralization of the rearrangement mass with ammonia yields 1.7 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. The novel chemistry is as follows ... 

IndChem 23, 17—24 (1947) (Ammonia oxidation process and concentration of nitric acid) 37) O.A. Hougen K.M. Watson, Chemical Process Principles , J. Wiley, NY, Combined volume (1947), 224 (Heat capacities of nitric acid) 38) W.M. Latimer J.H. Hildebrand, Reference Book of Inorganic Chemistry , Macmillan, NY (1947), 202-207 39) S. 

There are various passivation chemistries commonly available. Some are better than others, but the strongest oxidizers produce the most effective passivation. The addition of air to the boiler during passivation improves weaker passivators such as ammonia/hydrazine. Chemistries include ... 

In view of the spectroscopic evidence available, particularly from coadsorption studies (see Chapter 2), ammonia oxidation at Cu(110) became the most thoroughly studied catalytic oxidation reaction by STM. However, a feature of the early STM studies was the absence of in situ chemical information. This was a serious limitation in the development of STM for the study of the chemistry of surface reactions. What, then, have we learnt regarding oxygen transient states providing low-energy pathways in oxidation catalysis ... 

Fig. 18. PECVD TEOS oxide slurry removal efficiency in ammonia-based chemistries (0.25, 6) performed at 55°C during 10 min. Diluted ammonia with megasonics gives results as good as the scrubber.

The chemistry of ammonia oxidation is remarkably simple with only six main reactions that need to be considered. There are also... 

The gas feed for ammonia oxidation is normally oxygen rich ( 10% NHa/air stoicheiometric ratio 14% NHs/air) but the Andrussow HCN process is operated on the fuel-rich side of stoicheiometric [(CH4 + NH3VO2 = 1.5]. The likely surface chemistry under both conditions is therefore of interest. 

Present-day nitric acid production is almost entirely via the oxidation of ammonia and absorption of the oxidation products in water. The chemistry of this process was proven experimentally by Kuhlmann in 1839, but had to wait for the development of an economical route to ammonia before it could become commercially significant [38]. Ostwald, working in Germany in about 1900, reexamined and extended Kuhlmann s data and established the proper conditions required for the ammonia oxidation step. Very shortly after this plants operating on these principles were constructed both in Germany and the U.S. Since 1980, 3-5 million metric tonnes of nitric acid (100% basis) have been produced annually in Germany, and 7-9 million tonnes in the U.S. (Table 11.7). 

First-principle quantum chemical methods have advanced to the stage where they can now offer qualitative, as well as, quantitative predictions of structure and energetics for adsorbates on surfaces. Cluster and periodic density functional quantum chemical methods are used to analyze chemisorption and catalytic surface reactivity for a series of relevant commercial chemistries. DFT-predicted adsorption and overall reaction energies were found to be within 5 kcal/mol of the experimentally known values for all systems studied. Activation barriers were over-predicted but still within 10 kcal/mol. More specifically we examined the mechanisms and reaction pathways for hydrocarbon C-H bond activation, vinyl acetate synthesis, and ammonia oxidation. Extrinsic phenomena such as substituent effects, bimetallic promotion, and transient surface precursors, are found to alter adsorbate-surface bonding and surface reactivity. 

To test the reaction mechanism pure ammonia-oxygen-diluent flames were studied under a wide range of stoichiometries and dilutions. Peterson and Laurendeau(23) had previously studied NH3 doped flames which elucidate much of the NHi oxidation chemistry. The present experiments probe the same reactions and also reactions between nitrogeneous species. Flame speeds were first considered in order to establish a subset of literature reaction rates which would describe this major flame feature. Comparison of the other flame features confirm that the flame speed is a good test bed for the reaction mechanism. 

Ammonia Oxidation with Pt + Ion-Exchanged Zeolite Catalysts Catalysis Through Coordination Chemistry... 

The ammonia oxidation reaction, which is catalyzed by a Pt + complex, proceeds via the rapid formation of a Pt(NH3)3NO complex. This complex is generated by the oxidation of Pt(NH3) in which an H+ is accepted by a basic lattice oxygen atom in the zeolite and H2O is generated. The zeolite lattice oxygen atom takes over the role of the basic ligands in organometaUic chemistry or the role of the proton-accepting water molecules. 

Daniele, S., Baldo, M.A., Bragato, C. et al. (2002) Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia. Analytical Chemistry, 74,3290-3296. 

Another interesting feature of the diazo-oxide chemistry is the possibility to decarboxylate the indene carboxylic acid by thermal activation in the presence of a catalyst (e.g. ammonia)... 

In its chemistry, cadmium exhibits exclusively the oxidation state + 2 in both ionic and covalent compounds. The hydroxide is soluble in acids to give cadmium(II) salts, and slightly soluble in concentrated alkali where hydroxocadmiates are probably formed it is therefore slightly amphoteric. It is also soluble in ammonia to give ammines, for example Of the halides, cadmium-... 

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