Ammonia oxidation system

Figure 18-19 The ammonia oxidation system of the bacterium Nitrosomonas. Oxidation of ammonium ion (as free NH3) according to Eq. 18-17 is catalyzed hy two enzymes. The location of ammonia monooxygenase (step a) is uncertain but hydroxylamine oxidoreductase (step b) is periplas-mic. The membrane components resemble complexes I, III, and IV of the mitochondrial respiratory chain (Fig. 18-5) and are assumed to have similar proton pumps. Solid green lines trace the flow of electrons in the energy-producing reactions. This includes flow of electrons to the ammonia monoxygenase. Complexes HI and IV pump protons out but complex I catalyzes reverse electron transport for a fraction of the electrons from hydroxylamine oxidoreductase to NAD+. Modified from Blaut and Gottschalk.315...

Some aspects of fluidized-bed reactor performance are examined using the Kunii-Levenspiel model of fluidized-bed reactor behavior. An ammonia-oxidation system is modeled, and the conversion predicted is shown to approximate that observed experimentally. The model is used to predict the changes in conversion with parameter variation under the limiting conditions of reaction control and transport control, and the ammonia-oxidation system is seen to be an example of reaction control. Finally, it is shown that significant differences in the averaging techniques occur for height to diameter ratios in the range of 2 to 20. 

Suzuki I, Chan CW, Takeuchi TL (1992) Oxidation of elemental sulfur to sulfite by Thiobacillus thiooxidans cells. Appl Environ Microbiol 58 3767-3769 Suzuki I, Dular U, Kwok S-C (1974) Ammonia or ammonium ion as substrate for oxidation by Nitrosomonas europaea cells and extracts. J Bacteriol 120 556-558 Suzuki I, Kwok S-C (1970) Cell-free ammonia oxidation by Nitrosomonas europaea effects of polyamines, Mg2+ and albumin. Biochem Biophys Res Commun 39 950-955 Suzuki I, Kwok S-C (1981) A potential resolution and reconstitution of the ammonia oxidizing system of Nitrosomonas europaea. Role of cytochrome c-554. Can J Biochem 59 484-488... 

In the ammonia oxidation system shown in Fig. 18, ammonia is adsorbed in the presence of oxygen on Cu(l 11). At lower surface coverages, atomic oxygen increases the adsorption energy of ammonia by 30 kJ/mol. The adsorption energy for ammonia in the presence of oxygen is -48... 

Above pH 9, decomposition of ozone to the reactive intermediate, HO, determines the kinetics of ammonia oxidation. Catalysts, such as WO, Pt, Pd, Ir, and Rh, promote the oxidation of dilute aqueous solutions of ammonia at 25°C, only two of the three oxygen atoms of ozone can react, whereas at 75°C, all three atoms react (42). The oxidation of ammonia by ozone depends not only on the pH of the system but also on the presence of other oxidizable species (39,43,44). Because the ozonation rate of organic materials in wastewater is much faster than that of ammonia, oxidation of ammonia does not occur in the presence of ozone-reactive organics. 

Ammonia production by partial oxidation of hydrocarbon feeds depends to some degree on the gasification step. The clean raw synthesis gas from a Shell partial oxidation system is first treated for sulfur removal, then passed through shift conversion. A Hquid nitrogen scmbbiag step follows. 

Ammonia oxidation was a prototype system, but subsequently a number of other oxidation reactions were investigated by surface spectroscopies and high-resolution electron energy loss spectroscopy XPS and HREELS. In the case of ammonia oxidation at a Cu(110) surface, the reaction was studied under experimental conditions which simulated a catalytic reaction, albeit at low... 

Simultaneously with the STM studies, Kulkarni et al,14 in Cardiff studied by XPS and HREELS the interaction of ammonia with Ni(l 10)-O and Ni(100)-0 surfaces. There was evidence in the N(ls) spectra for more than one nitrogen state present including N(a), but differentiating between NH(a) and NH2(a) was not possible. The intensity in the N(ls) spectrum region was broad over the range 397-400 eV. As the oxygen coverage increased to >0.3, the oxide O2 component became more prominent and the activity for ammonia oxidation decreased, as was observed by STM. Similar conclusions were reached for water interaction with the Ni(110)-O system.15... 

The main reactions, which have to be considered on SCR catalysts, are the standard-SCR, fast-SCR, and the N02-SCR reactions, beside the ammonia oxidation and the formation of N20. The fast-SCR reaction is promoted by N02 in the feed that can be generated from NO in a pre-oxidation catalyst. However, the right dimensioning of the oxidation catalyst is critical in order to prevent the production of an excess of hazardous N02. This problem is further aggravated if a continuous regenerating DPF is installed in front of the SCR system, as part of the N02 produced by the oxidation catalyst is always consumed in the filter for soot oxidation. 

S02 and NOx in flue gas from coal combustion contribute to smog and acid rain. Methods to remove these pollutants include alkaline wet scrubber systems that fix S02 to solid CaS04, and selective catalytic reduction by metal/metal oxide systems of NO/NOz to N2 and steam in the presence of ammonia. Particulate active carbons have also been used in flue gas decontamination, especially as they avoid costly scrubber processes and can operate at lower temperatures. The potential of active carbon fibers in this application has been explored by a... 

Kf., while not quantified experimentally, was recently introduced by Kirby and coworkers on the basis of product formation from O-attack at electrophilic P and C centers, as well as MO calculations incorporating the novel species, ammonia oxide, NH3+-0 . In common with other ambident nucleophiles, factors such as electronic, steric, kinetic and thermodynamic effects will determine actual extant pathways in a given system. Af-substituted hydroxylamines (see Scheme 1) can in principle partake of the equilibria shown in Scheme 2. Again, actual outcomes will be influenced by the aforementioned criteria. 

To describe the NH3 + NO + O2 (standard SCR) reacting system, NH3 adsorption-desorption, ammonia oxidation to nitrogen and standard SCR have been considered with the kinetics already presented in the previous section. 

To describe the NH3 + NO/NO2 reaction system over a wide range of temperatures and NO2 NOxfeed ratios in addition to ammonia adsorption-desorption, ammonia oxidation and standard SCR reaction with the associated kinetics already discussed in Section 2.3.2, the following reactions and kinetics have been considered by Chatterjee and co-workers [79] ... 

In 1959, Idol (2), and in 1962, Callahan et al. (2) reported that bismuth/molybdenum catalysts produced acrolein from propylene in higher yields than that obtained in the cuprous oxide system. The authors also found that the bismuth/molybdenum catalysts produced butadiene from butene and, probably more importantly, observed that a mixture of propylene, ammonia, and air yielded acrylonitrile. The bismuth/molybdenum catalysts now more commonly known as bismuth molybdate catalysts were brought to commercial realization by the Standard Oil of Ohio Company (SOHIO), and the vapor-phase oxidation and ammoxidation processes which they developed are now utilized worldwide. 

The multiplicity phenomenon in chemically reactive systems was first observed in 1918 by Liljenroth [1] for ammonia oxidation and it later appeared in the Russian literature of the 1940s [2]. However, it was not until the 1950s that major investigations of this phenomenon began. This development was inspired by the Minnesota school of Amundson and Aris and their students [3-5]. The Prague school also had a notable contribution in expanding the field [13-16]. 

Nitrate Reductases. These enzymes have two important functions (38). They serve as a terminal oxidation system in some microorganisms, and in many microorganisms, molds, fungi, and higher plants they are utilized in the assimilation of nitrogen into the cell via production of ammonia, which is subsequently metabolized into cell components. 

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