Showing papers on "Ammonia published in 2000"
TL;DR: In this paper, a Solid Polymer Electrolyte Cell (SPE) was used to synthesize ammonia from nitrogen and water at Ru cathodes, at atmospheric pressure and low temperature.
392 citations
TL;DR: A review of the literature on the chemical reduction of nitrate in aqueous systems has found about a hundred articles dealing with nitrate removal from such systems, with the majority having been published over the last decade as discussed by the authors.
278 citations
TL;DR: The assimilation of inorganic N, in the form of ammonia, onto C skeletons for the production of amino acids is one of the most important biochemical processes in plants.
Abstract: The assimilation of inorganic N, in the form of ammonia, onto C skeletons for the production of amino acids is one of the most important biochemical processes in plants. In an actively growing plant, N is taken up as nitrate and to a lesser extent as ammonia. Nitrate is reduced in the cytoplasm by
231 citations
TL;DR: In this article, a model of a V2O5-MoO3-TiO2 DeNOx catalyst has been presented and briefly characterized, and the adsorption of urea on it has also been investigated.
Abstract: A model V2O5–MoO3–TiO2 DeNOx catalyst has been prepared and briefly characterized. The adsorption of urea on it (and of ammonia for comparison) has also been investigated. It has been observed that urea can adsorb over the catalyst in an anionic form that can later decompose to isocyanate anions and ammonia and ammonium ion species. This mechanism suggests that the potential reactivity of the anionic form of urea and of isocyanate anions with VOCs, if they are present in the waste gas, possibly rise to polluting compounds must be taken into account for applications of the urea/DeNOx process.
213 citations
Patent•
27 Sep 2000
TL;DR: In this paper, a single-stage process was described for the preparation of primary aliphatic polyamines of the formula in which R 1 and R 2 independently of one another are hydrogen, methyl, ethyl or aminomethyl, by reaction of polyalcohols on a Co/Ni catalyst with supercritical ammonia.
Abstract: A single-stage process is described for the preparation of primary aliphatic polyamines of the formula in which R 1 and R 2 independently of one another are hydrogen, methyl, ethyl or aminomethyl, by reaction of polyalcohols on a Co/Ni catalyst with supercritical ammonia in the presence of hydrogen.
174 citations
TL;DR: In this paper, the authors used a gold amalgam (Au/Hg) voltammetric microelectrode to measure the distributions of O 2, Mn(II), Fe(II, I(2I), I (2I) and HS(2) in bioturbated sediment cores from the Laurentian Trough.
173 citations
TL;DR: In this article, the authors investigated the effect of ammonium ions (NH+4) and ammonium (NH3) on the growth rate of the duckweed Spirodela polyrrhiza and found that ammonium is the preferred nitrogen source of the plant but at certain levels it may become inhibitory to the plant.
171 citations
TL;DR: In this article, a combination of dielectric barrier discharge plasma and a monolithic V2O5-WO3/TiO2 catalyst using ammonia as a reducing agent was studied in synthetic gas mixtures at temperatures between 100 and 250°C.
Abstract: The selective catalytic reduction (SCR) of nitrogen oxides (NOx) by a combination of dielectric barrier discharge plasma and a monolithic V2O5-WO3/TiO2 catalyst using ammonia as a reducing agent was studied in synthetic gas mixtures at temperatures between 100 and 250°C. The mixtures were similar to diesel exhaust gases. For gas mixtures (NOx,0=NH3,0=500 ppm) in which 95% of the nitrogen oxides were in the form of NO, the removal of NOx below 140°C without plasma treatment was negligible. Treating the gas mixture with dielectric barrier discharges before the catalytic conversion, about 70% of the NOx was reduced at temperatures as low as 100°C. By plasma treatment 170 ppm of the NO was converted, 110 ppm by oxidation to NO2 and 60 ppm by reduction with products of NH3. Due to the coexistence of NO and NO2 on the catalyst, the selective catalytic reduction was enhanced. Similar effects were observed for the selective catalytic reduction in gas mixtures containing equal amounts of NO and NO2 without plasma treatment. Relative reaction rates for different NOx-reducing reactions over the catalyst are evaluated using a macroscopic model.
154 citations
TL;DR: In this article, a hydroxide-bridged dinuclear nickel complex with a urea molecule linking the two metal ions through its carbonyl oxygen atom has been prepared as a model for the metalloenzyme urease.
Abstract: A hydroxide-bridged dinuclear nickel complex with a urea molecule linking the two metal ions through its carbonyl oxygen atom has been prepared as a model for the metalloenzyme urease. This complex, [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3, where bdptz is the dinucleating ligand 1,4-bis(2,2‘-dipyridylmethyl)phthalazine, effects the hydrolysis of urea upon heating in a two-step reaction. In the first step, a molecule of ammonia is eliminated from urea with concomitant production of cyanate, the first-order rate constant in acetonitrile being (7.7 ± 0.5) × 10-4 h-1. This reaction is at least 500 times faster than the spontaneous decomposition of urea under the same conditions. When the cyanate-containing product is further heated in the presence of water, the cyanate is hydrolyzed with a second-order rate constant of (9.5 ± 1) × 10-4 M-1 h-1. Reaction of [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3 in 50% aqueous acetonitrile afforded ammonia with no appreciable buildup of the cyanate-containing spe...
146 citations
TL;DR: In this article, a microkinetic model for catalytic ammonia synthesis over non-promoted ruthenium is developed, based mostly on results from surface science investigations, where Nitrogen dissociation is assumed to be the rate-determining step.
140 citations
TL;DR: Ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid state proton-conducting cell reactor as discussed by the authors, where two types of reactors were used, one doublechamber and one single-chamber cell.
TL;DR: In this article, the decomposition and reactivity of NH4HSO4 in situ formed on various V2O5/AC and V2 O5/TiO2 catalysts were studied in detail using a temperature-programmed method.
TL;DR: In this article, a mechanism for ammonia oxidation to nitrogen is proposed wherein part of the ammonia fed to the catalyst is converted into nitric oxide, and a pool of monoatomic surface nitrogen species of varying oxidation states is established.
TL;DR: In this article, high quality β zeolite (BEA) with a Si/Al 2 ratio of 30:70 was readily prepared by a dry gel conversion method, and the acidity was measured by an improved technique of temperature programmed desorption of ammonia.
TL;DR: The higher α-amylase productivity during growth on casein hydrolysate was not caused by increased transcription of the α-AMylase genes but was caused by a faster secretion of α-Amylase or by a lower binding of α -amyl enzyme to the biomass.
Abstract: The influence of the nitrogen source on the α-amylase productivity of Aspergillus oryzae was quantified in continuous cultivations. Both inorganic and complex nitrogen sources were investigated and glucose was used as the carbon and energy sources. For production of α-amylase, nitrate was shown to be inferior to ammonia as a nitrogen source. A mixture of ammonia and complex nitrogen sources, such as yeast extract or casein hydrolysate, was better than with ammonia as the sole nitrogen source. Even a low concentration of casein hydrolysate (0.05 g l−1) resulted in a 35% increase in the α-amylase productivity. The higher α-amylase productivity during growth on casein hydrolysate was not caused by increased transcription of the α-amylase genes but was caused by a faster secretion of α-amylase or by a lower binding of α-amylase to the biomass.
TL;DR: Fe-ZSM-5 showed the best catalytic performance (nearly 100% N2 yield) and resistance to water vapor for selective catalytic N2oxidation of NH3 to N2 at a high gas hourly space as discussed by the authors.
TL;DR: In this paper, the ammonia removal by physical chemical treatment from young leachate and anaerobically treated young landfill leachates was experimentally investigated, and the results showed that up to 80% COD removal was obtained with MAP precipitation of raw leACHate.
TL;DR: In this paper, a coulometric flow titration with electrogenerated bromine was combined with chemiluminescent and amperometric flow detection to determine low concentrations of hydrazine and ammonium.
01 Jan 2000
TL;DR: In this article, Schulze et al. describe the major processes in the soil nitrogen cycle, which is defined as the biotic conversion of organic N into inorganic N, mainly NH4 + and NO3 −.
Abstract: Mineralisation, nitrification and denitrification are major processes in the soil nitrogen cycle (see Schulze, Fig. 1.2, this Vol. Chap. 1). Nitrogen (N) mineralisation is by definition the biotic conversion of organic N into inorganic N, mainly NH4 + and NO3 −. Many organism groups, bacteria, fungi and certain soil animals, possess this capability, and the product formed is generally ammonia/ammonium, depending on the soil pH. Ammonium (NH4 +) can be oxidised via nitrite (NO2 − to nitrate (NO3 −. Both chemoautotrophic (using CO2 as a C source) and heterotrophic (using organic C as a C source) microorganisms can perform this nitrification process (Prosser 1986). Heterotrophic microorganisms can also produce nitrate directly from organic N sources (Killham 1986). Nitrate can be reduced via nitrite to nitric oxide (NO), nitrous oxide (N2O) and/or dinitrogen (N2) (denitrification). In addition to these processes, ammonium/ammonia, nitrite and nitrate can be assimilated (immobilised) by microorganisms, mycorrhizal fungi and roots. Further, ammonia and nitrite are known to react with certain organic compounds and, thus, be chemically immobilised (Nommik and Vahtras 1982; Azhar El Sayed et al. 1986).
TL;DR: In this paper, the authors observed octahedral aluminum species connected to the framework structure of zeolite Beta, and these aluminum sites exhibit characteristics of Lewis acid sites, which are created by partial hydrolysis of framework Si-O-Al bonds; they convert reversibly to tetrahedral aluminum sites upon aqueous NH+4 exchange or reaction with NH3 gas.
TL;DR: In the biofiltration system utilized in this study, the shortest retention time that the system could attain was 0.532min, but the retention time can be decreased further without decreasing the ammonia removal efficiency.
TL;DR: In this paper, a microbial process was developed for the removal of ammonia from simulated mine effluents, which is accomplished in two steps in the first step, ammonia is oxidized to nitrate, and in the second step, nitrate is reduced to dinitrogen gas.
TL;DR: In this paper, the saturating reaction of ammonia on trimethylaluminum (TMA)-modified porous silica was studied from 423 to 823 K. This reaction step completes a reaction cycle of TMA and ammonia in aluminum nitride growth by ALCVD, a technique based on well-separated saturating gas−solid reactions.
Abstract: The saturating reaction of ammonia was studied on trimethylaluminum (TMA)-modified porous silica. This reaction step completes a reaction cycle of TMA and ammonia in aluminum nitride growth by atomic layer chemical vapor deposition (ALCVD), a technique based on well-separated saturating gas−solid reactions. The reaction was studied from 423 to 823 K. In addition, the separate reactions of TMA at 423 K and ammonia at 823 K were studied on silica dehydroxylated at 1023 K. The reaction products on the surface were identified by IR and 29Si, 13C, and 1H NMR spectroscopy, and they were quantified by element determinations and 1H NMR. In the reaction of TMA on silica, methyl groups were attached to the surface indirectly through aluminum and through direct bonding to silicon. In the subsequent ammonia reaction, ligand exchange of ammonia with the methyl groups occurred at all reaction temperatures, resulting in primary amino groups and the release of methane. Also, secondary amino groups were found on the surfa...
TL;DR: The ability of several alumina-supported metal catalysts and transition-metal ion-exchanged zeolite Y catalysts to oxidize ammonia to nitrogen and water at low temperatures (between 200 and 350°C) was tested both at high and low ammonia concentrations as mentioned in this paper.
TL;DR: In this article, the relaxed eddy-accumulation technique (REA) was used to measure ammonia fluxes over a corn field after urea application, and denuder tubes, coated with oxalic acid, were used at the inlet of the REA system to trap ammonia in air.
Abstract: Ammonia emissions from fertilized fields not only decrease the fertilizer value but also contribute to environmental pollution in the form of off-site deposition. Quantifying the magnitude of ammonia fluxes is therefore of great interest because of economical and environmental aspects. Two factors make ammonia flux measurements particularly challenging: (i) ammonium in particulate phase often interferes with gas phase ammonia and (ii) ammonia is easily adsorbed on surfaces. Due to the lack of a suitable fast-response ammonia sensor, we decided to explore the feasibility of using denuder tubes with the relaxed eddy-accumulation technique (REA) for measuring ammonia fluxes. In the spring of 1996, the REA technique was successfully used to measure ammonia fluxes over a corn field after urea application. The denuder tubes, coated with oxalic acid, were used at the inlet of the REA system to trap ammonia in air. During the 23 days of measurements, ammonia emission rates ranged from 1 to 1023 ng NH3 m-2 s-1, a...
TL;DR: A nitrogen flux model is described, in which the product of symbiont nitrate reduction, ammonia, is the primary source of nitrogen for the host and the symbionts and fulfills the association's nitrogen needs via incorporation of ammonia into amino acids.
Abstract: The hydrothermal vent tubeworm Riftia pachyptila lacks a mouth and gut and lives in association with intracellular, sulfide-oxidizing chemoautotrophic bacteria. Growth of this tubeworm requires an exogenous source of nitrogen for biosynthesis, and, as determined in previous studies, environmental ammonia and free amino acids appear to be unlikely sources of nitrogen. Nitrate, however, is present in situ (K. Johnson, J. Childress, R. Hessler, C. Sakamoto-Arnold, and C. Beehler, Deep-Sea Res. 35:1723–1744, 1988), is taken up by the host, and can be chemically reduced by the symbionts (U. Hentschel and H. Felbeck, Nature 366:338–340, 1993). Here we report that at an in situ concentration of 40 μM, nitrate is acquired by R. pachyptila at a rate of 3.54 μmol g−1 h−1, while elimination of nitrite and elimination of ammonia occur at much lower rates (0.017 and 0.21 μmol g−1 h−1, respectively). We also observed reduction of nitrite (and accordingly nitrate) to ammonia in the trophosome tissue. When R. pachyptila tubeworms are exposed to constant in situ conditions for 60 h, there is a difference between the amount of nitrogen acquired via nitrate uptake and the amount of nitrogen lost via nitrite and ammonia elimination, which indicates that there is a nitrogen “sink.” Our results demonstrate that storage of nitrate does not account for the observed stoichiometric differences in the amounts of nitrogen. Nitrate uptake was not correlated with sulfide or inorganic carbon flux, suggesting that nitrate is probably not an important oxidant in metabolism of the symbionts. Accordingly, we describe a nitrogen flux model for this association, in which the product of symbiont nitrate reduction, ammonia, is the primary source of nitrogen for the host and the symbionts and fulfills the association's nitrogen needs via incorporation of ammonia into amino acids.
TL;DR: In this article, a Ni catalyst was used for catalytic ammonia decomposition and light tar reduction in a fixed-bed gasifier with a space time of about 3 s at 800-900 degreesC and 12 atm.
Abstract: Catalytic ammonia decomposition and tar reduction by a Ni catalyst were studied using a feed gas from a pilot-scale pressurized fluidized-bed gasifier. Tests were conducted in a tubular fixed-bed reactor with a space time of about 3 s at 800-900 degreesC and 12 atm. Ammonia removals of 35-95% and light tar conversions of 90-95% were observed. The amount of the light hydrocarbons was found to have a negative effect on the ammonia decomposition. An ammonia concentration in the fuel gas, gas residence time, and catalytic bed temperature also had a significant influence on the ammonia removal efficiency. After the catalyst, CO2 and CO approached equilibrium values,but the content of H-2 and H2O was lower because of reactions with tar. The heating value of the fuel gas remained the same; The gasification efficiency increased by about 10%, mainly because of catalytic tar cracking. Deactivation of the catalyst was not observed in the fuel gas containing 50-150 ppm H2S and about 10 g/Nm(3) tar. (Less)
TL;DR: In a number of runs, stable plasma operation was attained at pressures close to atmospheric, and the use of microwave-plasma discharge within the flue gas was explored as a potential pollution-control method.
TL;DR: In this article, the temporal characteristics of annual volume-weighted average ammonium (NH4+) ion concentration in precipitation and local ammonia (NH3) emissions over the period 1982−1997 at Nat...
Abstract: The temporal characteristics of annual volume-weighted average ammonium (NH4+) ion concentration in precipitation and local ammonia (NH3) emissions are investigated over the period 1982−1997 at Nat...
TL;DR: In this paper, the relationship between the acidic property and the composition of a zeolite was precisely measured using Y- and mordenite-type samples with high aluminum contents, and it was suggested that the lack of acidity on the hydrogen form zeolites with high aluminium concentration is due to the destruction of crystal structure, which is in...
Abstract: The relationship between the acidic property and the composition of a zeolite was precisely measured using Y- and mordenite-type samples with high aluminum contents. The ammonium form zeolite was evacuated and heated to yield the hydrogen form, and subsequently, the ammonia adsorption and temperature-programmed desorption were carried out in-situ without exposure of the hydrogen form sample to humid atmosphere. The number of the desorbed ammonia, showing the acid amount, was approximately same to the number of [Al] − [Na] atoms over the experimental range. This is quite different from the conventionally observed relationship between the acidic property and composition, in which the acidity is absent at the high aluminum concentration where the secondary-neighboring aluminum species (Al−O−Si−O−Al) is formed. On the basis of the X-ray diffraction, it is suggested that the lack of acidity on the hydrogen form zeolite with high aluminum concentration is due to the destruction of crystal structure, which is in...