Topic
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.
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TL;DR: In this paper, the removal of iron, manganese and ammonia from groundwater originating from four different locations in northern Croatia was studied, and four pilot plants, mainly differing in their aeration systems and operation pressures, have been used.
109 citations
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TL;DR: In this article, the free energies of all reaction barriers for all steps in the mechanism and built these results into a kinetic Monte Carlo model for predicting steady state catalytic rates to compare with single-crystal experiments at 673 K and 20 atm.
Abstract: The Haber-Bosch industrial process for synthesis of ammonia (NH3) from hydrogen and nitrogen produces the millions of tons of ammonia gas annually needed to produce nitrates for fertilizers required to feed the earth’s growing populations. This process has been optimized extensively, but it still uses enormous amounts of energy (2% of the world’s supply), making it essential to dramatically improve its efficiency. To provide guidelines to accelerate this improvement, we used quantum mechanics to predict reaction mechanisms and kinetics for NH3 synthesis on Fe(111)—the best Fe single crystal surface for NH3 synthesis. We predicted the free energies of all reaction barriers for all steps in the mechanism and built these results into a kinetic Monte Carlo model for predicting steady state catalytic rates to compare with single-crystal experiments at 673 K and 20 atm. We find excellent agreement with a predicted turnover frequency (TOF) of 17.7 s–1 per 2 × 2 site (5.3 × 10–9 mol/cm2/sec) compared to TOF = 10 ...
109 citations
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TL;DR: Molecular tunnels between distant active sites have been identified in tryptophan synthase and glutamine phosphoribosyl pyrophosphate amidotransferase and are likely architectural features in an expanding list of enzymes.
Abstract: The amidotransferase family of enzymes utilizes the ammonia derived from the hydrolysis of glutamine for a subsequent chemical reaction catalyzed by the same enzyme. The ammonia intermediate does not dissociate into solution during the chemical transformations. A well-characterized example of the structure and mechanism displayed by this class of enzymes is provided by carbamoyl phosphate synthetase (CPS). Carbamoyl phosphate synthetase is isolated from Escherichia coli as a heterodimeric protein. The smaller of the two subunits catalyzes the hydrolysis of glutamine to glutamate and ammonia. The larger subunit catalyzes the formation of carbamoyl phosphate using 2 mol of ATP, bicarbonate, and ammonia. Kinetic investigations have led to a proposed chemical mechanism for this enzyme that requires carboxy phosphate, ammonia, and carbamate as kinetically competent reaction intermediates. The three-dimensional X-ray crystal structure of CPS has localized the positions of three active sites. The nucleotide bind...
108 citations
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TL;DR: The results suggest that the increase in pH often observed in the later stages of ripening is related to a decrease in electrolyte dissociation and/or an increase in the concentration of buffering proteins as well as to the formation of ammonia.
108 citations
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TL;DR: The rate of urea excretion by goldfish was dependent on the 24-hr experimental ammonia levels but was not affected by the concentration of ambient ammonia during acclimation or the duration of acclimations.
108 citations