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.

Ammonium Limitation Results in the Loss of Ammonia-Oxidizing Activity in Nitrosomonas europaea

Abstract: The effects of limiting concentrations of ammonium on the metabolic activity of Nitrosomonas europaea, an obligate ammonia-oxidizing soil bacterium, were investigated. Cells were harvested during late logarithmic growth and were incubated for 24 h in growth medium containing 0, 15, or 50 mM ammonium. The changes in nitrite production and the rates of ammonia- and hydroxylamine-dependent oxygen consumption were monitored. In incubations without ammonium, there was little change in the ammonia oxidation activity after 24 h. With 15 mM ammonium, an amount that was completely consumed, there was an 85% loss of the ammonia oxidation activity after 24 h. In contrast, there was only a 35% loss of the ammonia oxidation activity after 24 h in the presence of 50 mM ammonium, an amount that was not consumed to completion. There was little effect on the hydroxylamine oxidation activity in any of the incubations. The loss of ammonia oxidation activity was not due to differences in steady-state levels of ammonia monooxygenase (AMO) mRNA (amoA) or to degradation of the active site-containing subunit of AMO protein. The incubations were also conducted at a range of pH values to determine whether the loss of ammonia oxidation activity was correlated to the residual ammonium concentration. The loss of ammonia oxidation activity after 24 h was less at lower pH values (where the unoxidized ammonium concentration was higher). When added in conjunction with limiting ammonium, short-chain alkanes, which are alternative substrates for AMO, prevented the loss of ammonia oxidation activity at levels corresponding to their binding affinity for AMO. These results suggest that substrates of AMO can preserve the ammonia-oxidizing activity of N. europaea in batch incubations by protecting either AMO itself or other molecules associated with ammonia oxidation.

Process for the simultaneous absorption of sulfur oxides and production of ammonium sulfate

Abstract: Process for the removal of sulfur oxides from sulfur oxide-containing gas with simultaneous production of ammonium sulfate. The process is carried out by first passing hot sulfur oxide-containing gas through a prescrubber wherein the gas contacts saturated aqueous ammonium sulfate liquor which is recycled in the prescrubber, followed by passing the prescrubbed gas through an absorber wherein the prescrubbed gas contacts dilute aqueous ammonium sulfate liquor. The sulfur oxide in the sulfur oxide-containing gas is absorbed by the dilute aqueous ammonium sulfate liquor in the absorber, and scrubbed gas is removed from the absorber. The dilute aqueous ammonium sulfate liquor is treated with ammonia and air and the absorbed sulfur dioxide is converted to ammonium sulfate in the liquor. The dilute ammonium sulfate liquor is recycled into contact with the prescrubbed gas in the absorber. Dilute aqueous ammonium sulfate liquor is removed from the absorber and added to the saturated aqueous ammonium sulfate liquor in the prescrubber where it becomes saturated due to evaporation caused by the hot gas. Ammonium sulfate crystals form in the saturated aqueous ammonium sulfate liquor in the prescrubber are recovered as product from saturated aqueous ammonium sulfate withdrawn from the prescrubber.

A new family of metal borohydride ammonia borane complexes: Synthesis, structures, and hydrogen storage properties

Abstract: We report the first two examples of borohydride ammonia borane complexes: Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2. Their structures are successfully determined using a combination of X-ray diffraction and first-principles calculations. Both structures are composed of alternating layers of borohydride and ammonia borane. Examination of bond lengths indicates that this arrangement is stabilized via dihydrogen bonding between ammonia borane and their surrounding BH4−, and the interactions between ammonia borane ligands and cations. Our experimental results show that more than 10 wt% and 11 wt% hydrogen can be released from Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2, respectively. Negligible ammonia was detected compared to ammonia borane and its ammidoborane derivatives. Further improvements are needed to reduce borazine emission. Cycling studies show that decomposed Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2 can be partially hydrogenated under hydrogen pressures at high temperatures.