Showing papers on "Ammonia published in 2011"
TL;DR: It is shown that N2H4 is produced from the anammox substrates ammonium and nitrite and that nitric oxide is the direct precursor of N2 H4, which presents a new biochemical reaction forging an N–N bond and fills a lacuna in understanding of the biochemical synthesis of the N2 in the atmosphere.
Abstract: Two distinct microbial processes, denitrification and anaerobic ammonium oxidation (anammox), are responsible for the release of fixed nitrogen as dinitrogen gas (N(2)) to the atmosphere. Denitrification has been studied for over 100 years and its intermediates and enzymes are well known. Even though anammox is a key biogeochemical process of equal importance, its molecular mechanism is unknown, but it was proposed to proceed through hydrazine (N(2)H(4)). Here we show that N(2)H(4) is produced from the anammox substrates ammonium and nitrite and that nitric oxide (NO) is the direct precursor of N(2)H(4). We resolved the genes and proteins central to anammox metabolism and purified the key enzymes that catalyse N(2)H(4) synthesis and its oxidation to N(2). These results present a new biochemical reaction forging an N-N bond and fill a lacuna in our understanding of the biochemical synthesis of the N(2) in the atmosphere. Furthermore, they reinforce the role of nitric oxide in the evolution of the nitrogen cycle.
694 citations
TL;DR: A molecular iron complex that reacts with N2 and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations, which give structural and spectroscopic insight into N2 cleavage and N-H bond-forming reactions of iron.
Abstract: The most common catalyst in the Haber-Bosch process for the hydrogenation of dinitrogen (N(2)) to ammonia (NH(3)) is an iron surface promoted with potassium cations (K(+)), but soluble iron complexes have neither reduced the N-N bond of N(2) to nitride (N(3-)) nor produced large amounts of NH(3) from N(2). We report a molecular iron complex that reacts with N(2) and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations. The product has a Fe(3)N(2) core, implying that three iron atoms cooperate to break the N-N triple bond through a six-electron reduction. The nitride complex reacts with acid and with H(2) to give substantial yields of N(2)-derived ammonia. These reactions, although not yet catalytic, give structural and spectroscopic insight into N(2) cleavage and N-H bond-forming reactions of iron.
426 citations
TL;DR: It is demonstrated that SR-AOP is a promising landfill leachate treatment method because it appears to be more advantageous over hydroxyl radical (OH∙)-based advanced oxidation processes (HR-A OPs) because OH∙ almost does not oxidize ammonia.
356 citations
TL;DR: In this paper, a stable continuous stripping of ammonia from the anaerobic wastewater treatment plant effluent was obtained in the ammonia stripping bench plant, where the operating parameters in the trials were chosen in respect of the economically feasible operating conditions in a biogas plant.
286 citations
TL;DR: Investigating the fate of nitrogen species during nitrate reduction by nano-scale zero valent iron and related reaction mechanisms determines that nitrate was converted to ammonium ion followed by ammonia stripping under a strong alkaline condition, which leads to a decrease in the total aqueous nitrogen amount.
282 citations
TL;DR: In this paper, a fuel system for ammonia-fired internal combustion engines using metal ammine complexes as ammonia storage is analyzed, and it is shown that a fuel mixture with 10 vol.% hydrogen performs best with respect to efficiency and power.
195 citations
TL;DR: The metabolic pathways, which could potentially contribute to NO and N₂O production by AOB have been conceptually reconstructed under conditions especially relevant to engineered nitrogen-removal systems, and suggest that engineering designs that achieve low effluent aqueous nitrogen concentrations also minimize gaseous nitrogen emissions.
Abstract: Chemolithoautotrophic AOB (ammonia-oxidizing bacteria) form a crucial component in microbial nitrogen cycling in both natural and engineered systems. Under specific conditions, including transitions from anoxic to oxic conditions and/or excessive ammonia loading, and the presence of high nitrite (NO2−) concentrations, these bacteria are also documented to produce nitric oxide (NO) and nitrous oxide (N2O) gases. Essentially, ammonia oxidation in the presence of non-limiting substrate concentrations (ammonia and O2) is associated with N2O production. An exceptional scenario that leads to such conditions is the periodical switch between anoxic and oxic conditions, which is rather common in engineered nitrogen-removal systems. In particular, the recovery from, rather than imposition of, anoxic conditions has been demonstrated to result in N2O production. However, applied engineering perspectives, so far, have largely ignored the contribution of nitrification to N2O emissions in greenhouse gas inventories from wastewater-treatment plants. Recent field-scale measurements have revealed that nitrification-related N2O emissions are generally far higher than emissions assigned to heterotrophic denitrification. In the present paper, the metabolic pathways, which could potentially contribute to NO and N2O production by AOB have been conceptually reconstructed under conditions especially relevant to engineered nitrogen-removal systems. Taken together, the reconstructed pathways, field- and laboratory-scale results suggest that engineering designs that achieve low effluent aqueous nitrogen concentrations also minimize gaseous nitrogen emissions.
Abbreviations: AMO, ammonia mono-oxygenase; anammox, anaerobic ammonium oxidation; AOB, ammonia-oxidizing bacteria; BNR, biological nitrogen removal; HAO, hydroxylamine oxidoreductase; IPCC, Intergovernmental Panel on Climate Change; Nor, nitric oxide reductase; USEPA, U.S. Environmental Protection Agency
167 citations
TL;DR: A linear relationship between the N(2)O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N(4)(+)-N/L production, and pH was shown to have a major impact on the AOB enriched culture.
167 citations
TL;DR: The electrochemical oxidation of ammonia has been studied in the most detail in alkaline solution at platinized platinum as discussed by the authors, in which elemental nitrogen is formed at mildly positive potentials with near quantitative current efficiency through dimerization of partly dehydrogenated ammonia molecules NH x (ads).
162 citations
TL;DR: In this article, the applicability of the natural zeolite for simultaneous removal of ammonia and humic acid, two of the most encountered concurrent contaminants in the surface waters, was examined.
161 citations
TL;DR: High salinity content benefited the MFC performance increasing power production and decreasing the internal resistance, and the activity of nitrifier microorganisms was inhibited at high free ammonia concentrations.
TL;DR: In this paper, a two-stage process to produce hydrogen and methane from lipid-extracted microalgal biomass residues (LMBRs) was developed, and the biogas production and energy efficiency were compared.
TL;DR: In this article, the authors examined the formation of nitrate using hourly measurements of sulfate and nitrate and a multiphase chemistry box model (RACM+CAPRAM).
TL;DR: In this article, the capture of carbon dioxide by ammonia in both aqueous and non-aqueous solutions was investigated at atmospheric pressure and 273 K under different operating conditions, and a preliminary mechanistic interpretation of the catalytic reaction was also briefly presented and commented.
TL;DR: Data indicate a highly active nitrogen cycle (N-cycle) in these springs and suggest that ammonia oxidation may be a major source of energy fuelling primary production.
Abstract: thermophilus narG revealed sediment populations of 1.3-1.7 ¥ 10 6 copies g -1 sediment. These data indicate a highly active nitrogen cycle (N-cycle) in these springs and suggest that ammonia oxidation may be a major source of energy fuelling primary production.
TL;DR: The results reveal that the reactions between alkylamines and ammonium salts contribute to particle growth and alter the composition of ammonium sulfate and bisulfate aerosols in the atmosphere.
Abstract: The heterogeneous reactions between alkylamines and ammonium salts (ammonium sulfate and ammonium bisulfate) have been studied using a low-pressure fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) at 293 ± 2 K. The uptake of three alkylamines, i.e., monomethylamine, dimethylamine, and trimethylamine, on ammonium sulfate shows a displacement reaction of ammonium by aminium, evidenced by the release of ammonia monitored using protonated acetone dimer as the reagent ion. For the three alkylamines, the initial uptake coefficients (γ0) range from 2.6 × 10–2 to 3.4 × 10–2 and the steady-state uptake coefficients (γss) range from 6.0 × 10–3 to 2.3 × 10–4 and decrease as the number of methyl groups on the alkylamine increases. A different reaction mechanism is observed for the uptake of the three alkylamines on ammonium bisulfate, which is featured by an acid–base reaction (neutralization) with irreversible alkylamine loss and no ammonia generation and occurs at a rate lim...
TL;DR: The effect of surface chemistry (nature and amount of oxygen groups) in the removal of ammonia was studied using a modified resin-based activated carbon and FTIR analyses of the exhausted oxidized samples confirm both the formation of NH(4)(+) species interacting with the Brønsted acid sites, together with the presence ofNH(3) species coordinated, through the lone pair electron, to Lewis acid sites on the graphene layers.
Abstract: The effect of surface chemistry (nature and amount of oxygen groups) in the removal of ammonia was studied using a modified resin-based activated carbon. NH(3) breakthrough column experiments show that the modification of the original activated carbon with nitric acid, that is, the incorporation of oxygen surface groups, highly improves the adsorption behavior at room temperature. Apparently, there is a linear relationship between the total adsorption capacity and the amount of the more acidic and less stable oxygen surface groups. Similar experiments using moist air clearly show that the effect of humidity highly depends on the surface chemistry of the carbon used. Moisture highly improves the adsorption behavior for samples with a low concentration of oxygen functionalities, probably due to the preferential adsorption of ammonia via dissolution into water. On the contrary, moisture exhibits a small effect on samples with a rich surface chemistry due to the preferential adsorption pathway via Bronsted and Lewis acid centers from the carbon surface. FTIR analyses of the exhausted oxidized samples confirm both the formation of NH(4)(+) species interacting with the Bronsted acid sites, together with the presence of NH(3) species coordinated, through the lone pair electron, to Lewis acid sites on the graphene layers.
TL;DR: In this paper, a cobalt-free La0.6Sr0.4Fe0.8Sm0.2O3-δ composite cathode and SDC-ternary carbonate composite electrolyte was used for the synthesis of ammonia.
TL;DR: In this article, the authors compared applications of an alternative fertilizer with urease inhibitor to reduce ammonia volatilization with conventional urea, under certain environmental and soil conditions, such as pH (4.0, 5.5, 6.3 and 6.8), soil water content (5, 10 or 20 % moisture), temperature (18 or 35 oC), and application method (over the surface or soil-incorporated).
Abstract: Ammonia volatilization is an important process of N loss which decreases the use efficiency of N by plants when urea is applied on the soil surface. To overcome this problem, some chemical compounds were mixed with urea to inhibit the urease action. The purpose of this study was to compare applications of an alternative fertilizer with urease inhibitor to reduce ammonia volatilization with conventional urea, under certain environmental and soil conditions. Four experiments were carried out in 2007 and 2008, under laboratory conditions, with samples of a Humic Haplumbrept. The treatments varied according to each experiment in terms of soil conditions, such as pH (4.0, 5.5, 6.3 and 6.8), soil water content (5, 10 or 20 % moisture), temperature (18 or 35 oC), aside from the fertilizer physical state (solid or liquid) and application method (over the surface or soil-incorporated). The experimental units consisted of plastic trays into which 12 kg of soil (dry basis) were filled in a 15 cm layer. Ammonia gas traps were installed across the soil surface. Frequent measurements were performed during the first 28 days of soil-fertilizer incubation. The peak of ammonia volatilization from the soil occurred in the first week after the application of traditional urea, and two or three days later for urea with urease inhibitor. Ammonia loss was not always higher from conventional than from treated urea, nor from solid than from liquid fertilizers. Ammonia volatilization increased with increases in soil pH, temperature and N rate and was lower at the lowest (5 %) and highest (20 %) soil moisture content. For surface-applied fertilizers, the maximum daily N loss rate was 14 kg ha-1 and the total cumulative loss ranged from 2 to 50 % of the applied N, depending mainly on the physical state of the fertilizer, temperature and on soil moisture. Soil incorporation of urea fertilizers was the best option to minimize ammonia volatilization in all treatments.
TL;DR: In this paper, a co-precipitation method was used to synthesize ammonia from hydrogen and nitrogen under atmospheric pressure using CoFe 2 O 4 as catalyst and carbonate-LiAlO 2 composite as electrolyte respectively.
TL;DR: The kinetics of the interactions of aqueous ammonia with aqueously carbon dioxide/carbonate species has been investigated using stopped-flow techniques by monitoring the pH changes via indicators and a complete reaction mechanism has been established.
Abstract: The kinetics of the interactions of aqueous ammonia with aqueous carbon dioxide/carbonate species has been investigated using stopped-flow techniques by monitoring the pH changes via indicators. The reactions include the reversible formation of ammonium carbamate/carbamic acid. A complete reaction mechanism has been established, and the temperature dependence of all rate and equilibrium constants including the protonation constant of the amine between 15 and 45 °C are reported and analyzed in terms of Arrhenius, Eyring, and van’t Hoff relationships.
TL;DR: In this paper, the rate of carbon dioxide absorption by aqueous ammonia solvent has been studied by applying a newly built wetted wall column, and the model could successfully predict the experimental measurements of CO 2 in loaded ammonia solutions.
TL;DR: Microbial community structure analysis revealed that the phylum Firmicutes dominated in the ammonia production, but the community structure changed at different sludge retention times, and in dry anaerobic digestion, the dominant bacteria shifted from thephylum Thermotogae to Firmicute.
TL;DR: In this paper, the volumetric overall mass transfer coefficients (KGaV) for CO2 absorption into aqueous ammonia solutions were evaluated over ranges of main operating variables, that is, up to 15 kPa partial pressure of CO2, 61 −214 m3/(m 2·h) gas flow rate, 0.76 −3.06 m3/m2·h liquid flow rate and 2%∼16% ammonia mass fraction, and 20 −50 °C temperature.
Abstract: The absorption of carbon dioxide into aqueous ammonia solution using a packed column was investigated. The volumetric overall mass transfer coefficients (KGaV) for CO2 absorption into aqueous ammonia solutions were evaluated over ranges of main operating variables, that is, up to 15 kPa partial pressure of CO2, 61–214 m3/(m2·h) gas flow rate, 0.76–3.06 m3/(m2·h) liquid flow rate, 2%∼16% ammonia mass fraction, and 20–50 °C temperature. An empirical KGaV correlation for this system was proposed. Experimental results show that the mass transfer process in CO2 absorption into aqueous ammonia solution is mainly controlled by the resistance in the liquid phase and the ammonia concentration has a great effect on the overall mass transfer coefficient.
TL;DR: In this paper, 24-h PM2.5 samples were collected using Harvard Honeycomb denuder/filter-pack system during different seasons in 2006 and 2007 at an urban site in Guangzhou, China.
TL;DR: In this article, the effects of ammonium exchange and SiO2/Al2O3 molar ratios on the reaction of methanol to propylene (MTP) over Na-ZSM-5 and H-Z SM-5 zeolites have been studied in a fixed-bed flow reactor under the operating conditions of T = 500 °C, P = 1 atm, and WHSV = 6 h−1.
TL;DR: In this article, the effects of operation parameters, such as ammonia concentration, Mg2+ concentration, reaction temperature and ageing temperature on morphology of magnesium hydroxide nanoparticles were investigated.
TL;DR: In this paper, Mg-Cu-Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia.
Abstract: Mg–Cu–Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N2 was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range.
TL;DR: In this article, the surface characterization before and after exposure to ammonia was carried out using X-ray diffraction, Fourier transform infrared spectroscopy, potentiometric titration, X -ray photoelectron spectrography, Raman spectrograms, transmission electron microscopy, thermal analysis and nitrogen adsorption.
TL;DR: In this article, the authors focused on the selective catalytic oxidation of hydrogen sulfide (H 2 S) over vanadia supported on TiO 2 -pillared clay catalysts (V/Ti-PILC) in the presence of ammonia and water.