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.

A Kinetic Model for the Selective Catalytic Reduction of NOx with NH3 over an Fe-zeolite Catalyst

Abstract: The selective catalytic reduction of NOx with ammonia over all Fe-zeolite catalyst was investigated experimentally and a transient kinetic model was developed. The model includes reactions that describe ammonia storage and oxidation, NO oxidation, selective catalytic reduction (SCR) of NO and NO2, formation of N2O, ammonia inhibition and ammonium nitrate formation. The model call account for a broad range of experimental conditions in the presence of H2O, CO2 and O-2 at temperatures from 150 to 650 degrees C. The catalyst stores ammonia at temperatures up to 400 degrees C and shows ammonia oxidation activity from 350 degrees C. The catalyst is also active for the oxidation of NO to NO2 and the oxidation reaches equilibrium at 500 degrees C. The SCR of NO is already active at 150 degrees C and the introduction of equal amounts of NO and NO2 greatly enhances the conversion of NOx at temperatures up to 300 degrees C. The formation of N2O is negligible if small fractions of NO2 are fed to the reactor, but a significant amount of N2O is formed at high NO2 to NO ratios. An ammonia inhibition oil the SCR of NO is observed at 200 degrees C. This kinetic model contains 12 reactions and is able to describe the experimental results Well. The model was validated using short transient experiments and experimental conditions not used in the parameter estimation and predicted these new conditions adequately.

Interference Effect of Alcohol on Nessler’s Reagent in Photocatalytic Nitrogen Fixation

Abstract: Photocatalytic ammonia synthesis is another important reaction to mimic natural nitrogen fixation, which has attracted more and more attention. In recent reports, sacrificial agents are often used to promote charge separation, and high-activity photocatalysts are discovered by using Nessler’s reagent method as a detection technique of ammonia production. However, there is an open question on the rationality and accuracy of the ammonia production amount in the presence of the sacrificial agent and Nessler’s reagent detection method. In this report, P25 TiO2 is employed as a model photocatalyst and alcohol as sacrificial agent, and both Nessler’s reagent and cation exchange chromatography are employed as ammonia detection methods. The different ammonia production amount was found by the different detection method. HPLC and 1H NMR results indicate that carbonyl compounds (formaldehyde, acetaldehyde, and acetone) are produced in the reaction. When the carbonyl compound was added to the ammonia standard soluti...

Field investigations of ammonia exchange between barley plants and the atmosphere. I. Concentration profiles and flux densities of ammonia

Abstract: The exchange of ammonia between the atmosphere and the canopy of spring barley crops growing at three levels of nitrogen application (medium N, high N and excessive N) was studied over two consecutive growing seasons by use of micrometeorological techniques. In most cases, ammonia was emitted from the canopy to the atmosphere. The emission started around 2 weeks before anthesis, and peaked about or shortly after anthesis. The volatilization of ammonia only took place in the daytime. During the night-time, atmospheric ammonia was frequently aborbed by the canopy. Occasionally, plants in the medium and high N treatments also absorbed ammonia from the atmosphere during the daytime. Daytime absorption of ammonia never occurred in the excessive N canopy. The loss of ammonia from the canopy amounted in both years to 0.5–1.5 kg NH3-N ha−1 and increased with the N status of the canopy. In agreement with the small losses of ammonia, the content of 15N-labelled nitrogen in the plants did not decline during the grain-filling period. The experimental years were characterized by very favourable conditions for grain dry matter formation, and for re-utilization of nitrogen mobilized from leaves and stems. Consequently, a very high part of the nitrogen in the mature plants was located in grain dry matter (80–84% in 1989; 74–80% in 1990). The efficient re-utilization of nitrogen may have reduced the volatilization of ammonia.

Determination of Ammonia Oxidation Rate in Sub- and Supercritical Water

Abstract: The supercritical water oxidation of ammonia was investigated in two isothermal, isobaric plug-flow reactors constructed of stainless steel and having different surface-to-volume ratios, at temperatures ranging from 803 to 903 K and pressures ranging from 14 to 28 MPa for 1-min-scale residence time under oxygen addition of 53−267% of the main reaction stoichiometry. Ammonia was mainly converted to nitrogen, while low levels (<1.6%) of nitrous oxide and nitrate ions were also produced. Ammonia was oxidized through both homogeneous and heterogeneous mechanisms, with the heterogeneous reaction being predominant. Pressure had an important effect in the homogeneous phase, although it could be concealed by the catalytic effect of the wall when the surface-to-volume ratio was high. The reaction rates were calculated as 105.74 exp(−144.74/RT)[NH3]0.74[H2O]-1.93 for the homogeneous reaction and 107.74 exp(−166/RT)[NH3]0.89 for the heterogeneous phase (activation energies are in kJ·mol-1).