Nitrous oxide, formation

Cant, N.W., Angove, D.E. and Chambers, D.C. (1998) Nitrous oxide formation during the reaction of simulated exhaust streams over rhodium, platinum and palladium catalysts, Appl. Catal. B 17, 63. 

Martin, J.A., Yates, M., Avila, P. et al. (2007) Nitrous oxide formation in low temperature selective catalytic reduction of nitrogen oxides with V205/Ti02 catalysts, Appl. Catal. B... 

Clemens, J., J. Burkhardt, and H. Goldbach, Abiogenic Nitrous Oxide Formation on Aerosols, Atmos. Environ., 31, 2961-2964 (1997). 

P. Glarborg, K. Dam-Johansen, J.A. Miller, R.J. Kee, and M.E. Coltrin. Modeling the Thermal DeNOx Process in Flow Reactors. Surface Effects and Nitrous Oxide Formation. Int. J. Chem. Kinetics, 26 421-436,1994. 

The system of equations obtained from the stage steady-state conditions can be solved without simplifications (it is reduced to a quadratic equation). However, a simple approximate solution is sufficient, based on the rate of nitrous oxide formation, r(3), being much less than the sum (r(1) + r<2)) of the rates along the routes iV and jV<2). 

Calculated fc(5.39) value is extremely low, therefore, the contribution of stage (5.39) to nitrous oxide formation is negligibly small. As (5.39) 0, nitrous oxide synthesis rate will be determined from the following equation ... 

Thus, the gas-phase oxidation of nitrogen with hydrogen peroxide is rather complicated and consists of primary nitrous oxide formation (up to 20%). When nitrous oxide with the... 

Hulgaard, T., and Dam-Johansen, K. (1993) Homogeneous Nitrous oxide Formation and Destruction under Combustion Conditions. AIChE J., 39 (8), 1342-1354. 

It is generally agreed that in terrestrial ecosystems denitrification is a significant source of both N2 and N2O under natural and agricultural conditions. See Figure 17 for better understanding of nitrous oxide formation. 

Wetlands, including tropical and subtropical irrigated rice, have soil conditions suitable for both methane and nitrous oxide formation and, as a result, are major anthropogenic sources of atmospheric methane and nitrous oxide. Aerobic and anaerobic enviromnents existing in wetland soil-plant systems provide conditions for both production and consumption of methane and nitrous... 

Soils inclnding wetland soils are important sonrces of atmospheric nitrous oxide. A wide range of processes may produce nitrous oxide, as well as minor amounts of NO, but not all of these seem to be fully understood. The main biological processes of nitrous oxide formation in soils are shown in Figure 16.5. They include nitrification, denitrification, the dissimilatory reduction of nitrate to ammonium, and the assimilatory reduction of nitrate wherein N is incorporated in the cell biomass. Additionally, some NO and nitrous oxide may be released due to chemo-denitrification and pyro-denitrification. Of these processes, nitrification and denitrification are the most important with respect to nitrous oxide production. 

FIGURE 16.7 The critical redox potential for nitrous oxide formation in flooded soil. (From Smith et al., 1983.)... 

Redox zone with little methane or nitrous oxide formation... 

Ammonia oxidation is conducted on a pre-oxidised platinum sponge catalyst. Figure 20 shows the conversion and selectivity at 373 K. The same selectivity characteristics as on the reduced platinum sponge catalyst are observed (Fig. 14). Thus, a high oxygen surface coverage does not favour initial nitrous oxide formation. The main difference with the reduced platinum sponge is the faster deactivation of the pre-oxidised catalyst below 413 K. 

Fig. 1.10 Nitrous oxide formation in ammonia slip catalysts is promoted by high N0 NH3 ratios coming out of the SCR catalyst [45]...

At relatively low temperatures (200 °C), nitrogen is the only product. At higher temperatures, nitrous oxide formation begins passing through a maximum at 400 °C [28]. The desired nitric oxide (NO) begins to be formed at 300 °C and the yield of nitric oxide continues to increase with temperature. Most plants operate at about 900 °C. However, even at this temperature, both nitrogen and nitrous oxide are byproducts. 

In the SCR process, NOX impurities are reduced with added ammonia in the presence of some residual oxygen from the furnace. The main NOX reduction reactions are shown in Table 11.5 together with some of the undesirable oxidation reactions, which can both produce sulfur trioxide and waste some of the added ammonia. Between 0.6-0.9 moles of ammonia per mole of NOX are added to limit the aimnonia shp to downstream equipment where it would deposit as sulfates. NOX conversion is therefore hmited to between 60-90%. At low NOX levels, there is little conversion to itrous oxide. Nitrous oxide formation is also inhibited by water. Gas leaving the boiler is usually at a temperature in the range 300-430°C and contains dust Dust is removed in an elee-trostatic precipitator with little heat loss before sulfur dioxide is removed as gypsum by reaction with lime. Alternatively, sulfur dioxide can also be eonvert-ed to sulfuric acid. The effluent is then vented to atmosphere. In the first power plants to be retrofitted with SCR units there were three possible loeations for the catalyst bed ... 

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