N2O production

CO2, N2 and N2O production as a function of the catalyst potential, UWR> obtained at 62IK for fixed inlet pressures of NO and CO. A sharp increase in reaction rate and product is observed as the catalyst potential is reduced below 0 V, i.e., upon Na supply to the Pt catalyst. The selectivity to N2, Sn2, is enhanced from 17% to 62%. This dramatic enhancement in catalytic performance is due to (a) enhanced NO vs CO chemisorption on Pt with decreasing potential and (b) Na-induced dissociation of chemisorbed NO. 

At low temperatures, reaction towards N2 and N2O product formation preferentially occurs at the (100) surface, and hence a significant particle shape sensitivity is predicted. At higher temperatures when NO readily desorbs, overall activation barriers on the different surfaces tend to become similar and hence surface sensitivity becomes less. The high selectivity toward NO at higher temperatures relates... 

Poth M, DD Focht (1985) N kinetic analysis of N2O production by Nitrosomonas europaea an examination of nitrifier denitrification. Appl Environ Microbiol 49 1134-1141. 

Steady state measurements of NO decomposition in the absence of CO under potentiostatic conditions gave the expected result, namely rapid self-poisoning of the system by chemisorbed oxygen addition of CO resulted immediately in a finite reaction rate which varied reversibly and reproducibly with changes in catalyst potential (Vwr) and reactant partial pressures. Figure 1 shows steady state (potentiostatic) rate data for CO2, N2 and N2O production as a function of Vwr at 621 K for a constant inlet pressures (P no, P co) of NO and CO of 0.75 k Pa. Also shown is the Vwr dependence of N2 selectivity where the latter quantity is defined as... 

Firestone, M. K. and Davidson, E. A. (1989). Microbiological basis of NO and N2O production and consumption in soil. In "Exchange of Trace Gases Between Terrestrial Ecosystems and the Atmosphere", (M. O. Andreae and D. S. Schimel, Eds), pp. 7-21. John Wiley Sons, New York. 

The 8 N- and 8 0-values of atmospheric N2O today, range from 6.4 to 7.0%c and 43 to 45.5%c (Sowers 2001). Terrestrial emissions have generally lower 8-values than marine sources. The 8 N and 8 0-values of stratospheric N2O gradually increase with altitude due to preferential photodissociation of the lighter isotopes (Rahn and Wahlen 1997). Oxygen isotope values of atmospheric nitrous oxide exhibit a mass-independent component (Cliff and Thiemens 1997 Clifif et al. 1999), which increases with altitude and distance from the source. The responsible process has not been discovered so far. First isotope measurements of N2O from the Vostok ice core by Sowers (2001) indicate large and 0 variations with time (8 N from 10 to 25%c and 8 0 from 30 to 50%c), which have been interpreted to result from in situ N2O production via nitrification. 

Detailed and fundamental studies of the mechanistic aspects of the electrochemical reduction and oxidation of nitric oxide were carried out by the Eindhoven group [82, 83] on a series of metals (Pt, Pd, Rh, Ru, Ir, and Au) both in the case of polycrystalline and well-defined single-crystal surfaces. It was found that the reduction process at all metals studied shows a high selectivity with respect to N2O production at high potentials while at low potentials the formation of NH3 is the dominant... 

As the result of a study in which NO and N2O production was measured among several organisms (e.g., Al. faecalis) as a function of the partial pressure of O2, Anderson et al. (1993) concluded that heterotrophic nitrification may well be a significant source of N2O in microaerobic soils. 

Anderson, I. C., Poth, M., Homstead, j., and Burdige, D. (1993). A comparison of NO and N2O production by the autotrophic nitrifier Nicrosomonas europaea and the het-erotrophic nitriher Alcaligenes faecalis. Appl. Environ Microbiol. 59, 3525-3533. 

Estuaries have been shown to be active sites of N2O production. DIN loading to sediments was positively correlated with N2O fluxes, indicating that eutrophication may be linked with increases in global emissions of N2O. In fact, a model of DIN transport by world rivers and estuaries indicates that 90% of the denitrification in rivers and estuaries occurs in the northern hemisphere. 

Seitzinger, S.P., and Nixon, S.W. (1985) Eutrophication and the rate of denitrification and N2O production in coastal marine sediments. Limnol. Oceanogr. 30, 1332-1339. 

Usui, T., Koike, I., and Ogura, N. (2001) N2O production, nitrification and denitrification in an estuarine sediment. Estuar. Coastal Shelf Sci. 52, 769-781. 

Screening results for L8 in the 02-promoted oxidation showed the expected Rh > Pd > Pt activity plus a temperature dependence for the most active alloy catalysts. Eighty percent to 85% of Rh was preferred in the alloys below 350 °C, while at higher temperatures the most active library individuals contained just 70-80% Rh. The NO-promoted oxidation could also lead to production of N2O via an undesired secondary process that should preferably be minimized. The screening results (measured as N2 and N2O production) were often comparable in terms of metal reactivity, but N2O formation at different temperatures was indeed observed and could be minimized, selecting Rh-rich alloys at 600 °C as the best catalysts from L8. 

A Studies with cultures of Nitrosomonas sp. and Nitrosomonas oceanus of marine origin N2O yield=ratio of N2O production to N02 production. B N2O yield=ratio of N2O production to NH4 consumption C N2O yield=ratio of N2O production to NO3" production D N2O yield=ratio of AN2O/AOU in combination with Redfield stoichiometry E N2O yield=ratio of water-column integrated AN2O to water-column integrated nitrogen deficit. 

It is obvious that sedimentary denitrification and water-column nitrification seem to be the major N2O formation processes. However, the yield of N2O from both processes strongly depends on the local O2 concentrations, thus dissolved O2 is the key factor regulating N2O production (and its subsequent emissions to the atmosphere). Additionally, N2O distributions in estuaries show a pronounced seasonal variability. 

Barford, C. C., Montoya, J. P., Altabet, M. A., and Mitchell, R. (1999). Steady-state nitrogen isotope effects of N2 and N2O production in Paracoaus denitrificans. Appl. Environ. Microbiol. 65(3), 989—994. 

How do the physiological characteristics of the AOA compare with those of the AOB in terms of substrate affinity, light sensitivity, growth rates, oxygen requirements, N2O production, etc. I.e., are AOA and AOB regulated in the environment by similar factors ... 

Morel et al. (2001) Present data on the vertical and latitudinal distribution of N2O and estn. of fluxes across the sea-air and thermocline interfaces in tropical ocean waters north and south of Puerto Rico. Observations provide evidence for active N2O production in near-surface tropical waters... 

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