Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Ammonia-oxidizing bacteria are more responsive than archaea to nitrogen source in an agricultural soil

Abstract: In the majority of agricultural soils, ammonium (NH4+) is rapidly converted to nitrate (NO3−) in the biological ammonia and nitrite oxidation processes known as nitrification. The often rate-limiting step of ammonia oxidation to nitrite is mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4 N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kg N ha−1, and steer-waste compost (200 kg total N ha−1) over four seasons. DNA was extracted from the soil, and real-time PCR and 454-pyrosequencing were used to evaluate the quantity and diversity of the amoA gene which encodes subunit A of ammonia monooxygenase. Soil pH, nitrate pools, and nitrification potentials were influenced by ammonium and organic fertilizers after the first fertilization, while changes in AOB abundance and community structure were not apparent until after the second fertilization or later. The abundance of AOA was always greater than AOB but was unaffected by N treatments. In contrast, AOB abundance and community structure were changed significantly by ammonium fertilizers. Specific inhibitors of nitrification were used to evaluate the relative contribution of AOA and AOB to nitrification. We found that AOB dominantly contributed to potential nitrification activity determined at 1 mM ammonium in soil slurries and nitrification potential activity was higher in soils treated with ammonium fertilizers relative to control soils. However, AOA dominated gross nitrification activity in moist soils. Our result suggests that AOB activity and community are more responsive to ammonium fertilizers than AOA, but that in situ nitrification rate is controlled by ammonium availability in this agricultural soil. Understanding this response of AOA and AOB to N fertilizers may contribute to improving strategies for the management of nitrate production in agricultural soils.

An experimental, theoretical and kinetic-modeling study of the gas-phase oxidation of ammonia

Abstract: A complete understanding of the mechanism of ammonia pyrolysis and oxidation in the full range of operating conditions displayed by industrial applications is one of the challenges of modern combustion kinetics. In this work, a wide-range investigation of the oxidation mechanism of ammonia was performed. Experimental campaigns were carried out in a jet-stirred reactor and a flow reactor under lean conditions (0.01 ≤ Φ ≤ 0.375), such to cover the full range of operating temperatures (500 K ≤ T ≤ 2000 K). Ammonia conversion and the formation of products and intermediates were analyzed. At the same time, the ammonia decomposition reaction, H-abstractions and the decomposition of the HNO intermediate were evaluated ab initio, and the related rates were included in a comprehensive kinetic model, developed according to a first-principles approach. Low-temperature reactor experiments highlighted a delayed reactivity of ammonia, in spite of the high amount of oxygen. A very slow increase in NH3 consumption rate with temperature was observed, and a full reactant consumption was possible only ∼150–200 K after the reactivity onset. The use of flux analysis and sensitivity analysis allowed explaining this effect with the terminating effect of the H-abstraction on NH3 by O2, acting in the reverse direction because of the high amounts of HO2. The central role of H2NO was observed at low temperatures (T < 1200 K), and H-abstractions from it by HO2, NO2 and NH2 were found to control reactivity, especially at higher pressures. On the other side, the formation of HNO intermediate via NH2 + O = HNO + H and its decomposition were found to be crucial at higher temperatures, affecting both NO/N2 ratio and flame propagation.

Acrylic acid doped polyaniline as an ammonia sensor

Abstract: Chemically synthesised acrylic acid doped polyaniline (PANI:AA) has been utilised as an ammonia vapour sensor in a broad range of concentrations, viz. 1–600 ppm. The response, in terms of decrease in dc electric resistance on exposure to ammonia was observed. The change in resistance, ΔR, is found to increase linearly with NH3 concentration upto 58 ppm and saturates thereafter. The decrease in resistance has been explained on the basis of removal of proton from the free acrylic acid (AA) dopant by the ammonia molecules thereby rendering free conduction sites in the polymer matrix. These results are well supported by FTIR spectral analysis and the X-ray diffraction studies. The FTIR spectra show a remarkable increase in benzenoid and quinoid vibrations. Also, simultaneous appearance of COO− and ammonium ion vibrations is indicative of the interaction of ammonia molecules with acrylic acid. The degree of crystallinity was found to increase substantially upto 58 ppm concentration.

Non-aqueous gas diffusion electrodes for rapid ammonia synthesis from nitrogen and water-splitting-derived hydrogen

Abstract: Electrochemical transformations in non-aqueous solvents are important for synthetic and energy storage applications. Use of non-polar gaseous reactants such as nitrogen and hydrogen in non-aqueous solvents is limited by their low solubility and slow transport. Conventional gas diffusion electrodes improve the transport of gaseous species in aqueous electrolytes by facilitating efficient gas–liquid contacting in the vicinity of the electrode. Their use with non-aqueous solvents is hampered by the absence of hydrophobic repulsion between the liquid phase and carbon fibre support. Herein we report a method to overcome transport limitations in tetrahydrofuran using a stainless steel cloth-based support for ammonia synthesis paired with hydrogen oxidation. An ammonia partial current density of 8.8 ± 1.4 mA cm−2 and a Faradaic efficiency of 35 ± 6% are obtained using a lithium-mediated approach. Hydrogen oxidation current densities of up to 25 mA cm−2 are obtained in two non-aqueous solvents with near-unity Faradaic efficiency. The approach is then applied to produce ammonia from nitrogen and water-splitting-derived hydrogen. Non-polar gaseous reactants such as N2 and H2 exhibit low solubility and slow transport in non-aqueous solvents and conventional gas diffusion electrodes cannot avoid non-aqueous electrolyte penetration. Here, transport limitations and catalyst flooding in tetrahydrofuran are overcome by using a stainless steel cloth-based support for lithium-mediated ammonia synthesis paired with H2 oxidation.