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Showing papers on "Ammonia published in 1995"


Journal ArticleDOI
TL;DR: In this article, the reaction mechanism and catalytic cycle for the selective catalytic reduction of nitric oxide by ammonia over vanadia/titania catalysts has been elucidated by in situ on-line FTIR studies under steady-state conditions.

488 citations


Journal ArticleDOI
TL;DR: There are diverse physiological functions of nitrogen end products in different animal groups, including excretion, acid-base regulation, osmoregulation and buoyancy, and both invertebrates and vertebrates use nitrogen-containing organic compounds as intracellular osmolytes.
Abstract: There are diverse physiological functions of nitrogen end products in different animal groups, including excretion, acid-base regulation, osmoregulation and buoyancy. Animals excrete a variety of nitrogen waste products, but ammonia, urea and uric acid predominate. A major factor in determining the mode of nitrogen excretion is the availability of water in the environment. Generally, aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid. Ammonia, urea and uric acid are transported across cell membranes by different mechanisms corresponding to their different chemical properties in solution. Ammonia metabolism and excretion are linked to acid-base regulation in the kidney, but the role of urea and uric acid is less clear. Both invertebrates and vertebrates use nitrogen-containing organic compounds as intracellular osmolytes. In some marine invertebrates, NH4+ is sequestered in specific compartments to increase buoyancy.

393 citations


Journal ArticleDOI
TL;DR: In this paper, the catalytic activity in the reduction of NO by ammonia in the presence of oxygen (SCR process) is reported for CuO-TiO2 and for different catalysts belonging to the MgO-Fe2O3 system.

385 citations


Journal ArticleDOI
TL;DR: In this article, it has been shown that the NH3/HCN ratio is dependent on the heating rate of the fuel, which may result in higher NH3 ratio in the former types of reactors.

239 citations


Book
01 Jan 1995
TL;DR: In this article, the structure and surface chemistry of Industrial Ammonia Synthesis Catalysts and related properties are discussed. But they do not consider the effect of poisonings of ammonia synthesis catalysts.
Abstract: 1 Thermodynamic Properties in Ammonia Synthesis.- 2 Structure and Surface Chemistry of Industrial Ammonia Synthesis Catalysts.- 3 Ammonia Synthesis over Non-Iron Catalysts and Related Phenomena.- 4 Kinetics of Ammonia Synthesis and Decomposition on Heterogeneous Catalysts.- 5 Poisoning of Ammonia Synthesis Catalysts.- 6 Ammonia Production Processes.- 7 Ammonia Storage and Transportation-Safety.

159 citations


Journal ArticleDOI
TL;DR: In this paper, the anaerobic treatment of wastewaters from the seafood processing industry was studied in a 15 m3 industrial pilot-plant, where the adaptation of the biomass to the salinity and the antagonistic effects on sodium toxicity caused by the presence of other ions made it possible to operate at these high sodium concentrations.

144 citations


Journal ArticleDOI
TL;DR: In this article, the amounts of ammonia released from thermal degradation of amino acids were measured using the ammonia electrode method using an aqueous solution of each amino acid was adjusted to pH 8 and heated at 180 °C for 2 h in a stainless steel reactor.
Abstract: The amounts of ammonia released from thermal degradation of amino acids were measured using the ammonia electrode method. An aqueous solution of each amino acid was adjusted to pH 8 and heated at 180 °C for 2 h in a stainless steel reactor. Among the 19 amino acids studied, asparagine, aspartic acid, cysteine, and glutamine released large amounts of ammonia under the conditions employed. The effect of temperature on the generation of ammonia was studied for asparagine, asparatic, glutamine, glutamic acid, and cysteine.

140 citations



Journal ArticleDOI
TL;DR: Ammonia, pyridine and ammonium acetate were found to be extremely effective as inhibitors of Pd/C catalyzed benzyl ether hydrogenolysis.

138 citations


Journal ArticleDOI
TL;DR: To overcome growth inhibition in bioreactors a pH-controlled feeding strategy was developed and provides an effective method for the production of biomass of M. chlorophenolicum serving as the inoculum in remediation technologies.
Abstract: The inhibitory effect of ammonia on the growth of the polychlorinated xenobiotic-degrading bacterium Mycobacterium chlorophenolicum was examined. The strain is inhibited by both the ionized and nonionized forms of ammonia. At pH 6.9 50% reduction of the growth rate was observed at 6.8 g l−1 total ammonium. For 23 experiments performed in shake-flask culture at different pH values and ammonium concentrations a growth model based on the extended Monod kinetic fits the data with a deviation of 5.3%. To overcome growth inhibition in bioreactors a pH-controlled feeding strategy was developed for effective cultivation of M. chlorophenolicum at an ammonium level below 0.3 g l−1. The ammonium addition was controlled on-line by the stoichiometric interdependence of ammonium consumption and pH decline. With this on-line control strategy a biomass concentration as high as 26.2 g l−1 can be achieved within less than 1 week of cultivation, compared to a biomass concentration of 15.5 g l−1 in normal batch culture after 2 weeks of cultivation. The yield is also increased from 0.32 g to 0.43 g biomass (g glucose)−1. The strategy developed provides an effective method for the production of biomass of M. chlorophenolicum serving as the inoculum in remediation technologies.

119 citations


Journal ArticleDOI
01 Nov 1995-Fuel
TL;DR: In this paper, the effects of temperature, pressure, ammonia concentration and gas residence time on the efficiency of Ni-based catalysts in the IGCC process were investigated. But the results showed that two of the catalysts tested are capable of efficiency reducing the concentration of ammonia in the gas.

Journal ArticleDOI
TL;DR: In this article, microcalorimetric measurements and infrared spectroscopy of ammonia adsorption were used to characterize the acidic properties of sulfated zirconia catalysts.
Abstract: Microcalorimetric measurements and infrared spectroscopy of ammonia adsorption were used to characterize the acidic properties of sulfated zirconia catalysts. Reaction kinetic measurements forn-butane isomerization were conducted over catalysts that were selectively poisoned with controlled amounts of ammonia. Initial heats of ammonia adsorption on the strong acid sites of sulfated zirconia were 150–165 kJ/mol, and these sites contain Bronsted acid and possibly Lewis acid centers. Sulfated zirconia samples that show high activity for the isomerization ofn-butane possess Bransted acid sites of intermediate strength, with differential heats of ammonia adsorption between 125 and 140 kJ/mol. The results of selective poisoning of sulfated zirconia with ammonia confirm that Bransted acid sites of intermediate strength are active forn-butane isomerization at 423 K while not discounting a possible role of the stronger acid sites.

Journal ArticleDOI
TL;DR: Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia.
Abstract: Mixed ruminal bacteria were cultured with glucose, cellulose or no carbohydrate, and ammonium bicarbonate or casein hydrolysate. Changes in amounts of bacterial ammonia and non-ammonia N were measured. Ratios of N isotopes expressed as delta 15N (delta 15N) were measured by isotope ratio mass spectrometry. When bacteria were cultured with glucose and ammonium bicarbonate, bacterial delta 15N decreased from .9 to -5.8/1000 and residual ammonia delta 15N increased from -1.4 to 12.7/1000. Fractionation of N isotope occurred during ammonia incorporation because the difference between delta 15N of ammonia and delta 15N of bacteria (delta 15N) was 18.8/1000 (P .1), indicating no fractionation of N isotopes occurred during utilization of amino acids. The amount of bacterial N was highest at 24 h of incubation when cellulose was the carbohydrate source. At that time, delta 15N between ammonia and bacteria was 8.9/1000 when ammonia was the N source, but delta 15N between non-ammonia and bacteria was 1.7/1000 when casein hydrolysate was the N source. Bacterial N decreased after 24 h when cellulose was the source of carbohydrate. Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia. Fractionation of N isotopes during incorporation of ammonia N may be used as a marker to study N metabolism by ruminal bacteria.

Journal ArticleDOI
TL;DR: In this paper, high volume open face triple filter packs and cascade impactors were used together with ion-chromatographic analyses to measure gaseous nitric acid and particulate nitrate in addition to other trace species.

Journal ArticleDOI
TL;DR: In this paper, the kinetics of the selective catalytic reduction (SCR) of nitric oxide with ammonia over an 8 mol-% V 2 O 5 /TiO 2 catalyst was studied in the temperature range 180-380°C, with Nitric oxide and ammonia feed concentrations in the range 500-2500 ppm with excess of oxygen.
Abstract: The kinetics of the selective catalytic reduction (SCR) of nitric oxide with ammonia over an 8 mol-% V 2 O 5 /TiO 2 catalyst was studied in the temperature range 180–380°C, nitric oxide and ammonia feed concentrations in the range 500–2500 ppm with excess of oxygen. It was found that the reaction order with respect to ammonia strongly depends on reaction temperature, in contrast to the case of the reaction order with respect to nitric oxide. The apparent activation energy of the reaction for nitrogen formation depends more on the feed concentration of ammonia than of nitric oxide. This activation energy varies between 12 and 9 kcal mol −1 for ammonia concentrations in the range 500–2000 ppm. Temperature-programmed desorption (TPD) studies revealed the presence of three well-resolved ammonia peaks corresponding to desorption energies in the range 22–28 kcal mol −1 . Transient isotopic experiments with 18 O 2 showed that at 400°C only small amounts of lattice oxygen of V 2 O 5 can be exchanged with gaseous oxygen. Similar experiments with 15 NO showed also that only very small quantities of nitric oxide adsorbed on the catalyst surface from a mixture containing 15 NO/O 2 /He. The partial oxidation reaction of ammonia to nitrogen and nitrous oxide at 350°C was studied by steady-state tracing techniques. The results obtained suggest that at the level of ammonia conversion of 75% there is an appreciable amount of NH x intermediate species (8.3 μmol/g) which are found in the reaction pathway of nitrogen formation, but a small amount (0.4 μmol/g) is found in the reaction pathway of nitrous oxide formation. In addition, adsorption and desorption steps of ammonia must be considered as faster steps than those involved in reaction between adjacent adsorbed NH x species to form nitrogen and nitrous oxide.


Journal ArticleDOI
TL;DR: In this paper, the surface reactivity in NO conversion to N2 in the presence or absence of ammonia and oxygen of a copper-on-alumina catalyst was studied by pulse and step-change transient catalytic experiments.

Journal ArticleDOI
TL;DR: In this paper, the authors measured gaseous ammonia in the atmosphere of a dry bat cave containing several million insectivorous bats and revealed a peak concentration of 1779 ppm (0.96 mg/dm3).
Abstract: Direct measurements of gaseous ammonia in the atmosphere of a dry bat cave containing several million insectivorous bats revealed a peak concentration of 1779 ppm (0.96 mg/dm3). Observations indicate that the origin of the gaseous ammonia is rapid microbial decomposition of bat urea, not chitinous guano. Modelling of ammonia distribution and diffusion indicates that ammonia production at the Cueva del Tigre is ∼257 g NH3/day, equivalent to the decomposition of ∼454 g urea/day. Ammonia production is also characterized by significant isotopic fractionation favoring isotopically light (δ15N depleted) ammonia.

Journal Article
TL;DR: Although significant differences were observed in cellular contents, the biochemical composition of the nitrate, nitrite and urea-grown cells was very similar and the biochemical profile was more affected by the growth phase than by the N source.
Abstract: Cultures of the marine diatom Phaeodaetylum trieornutum were grown in nitrate, nitrite, ammonia or urea media. Nitrogen transformation efficiencies were close to 100% in cultures with nitrate, nitrite or urea, with productivities in dry biomass between 2.2 g.l-1 (urea) and 2.8 g.t 1 (nitrate). However growth in ammonia cultures ceased due to a drop in pH of the medium. The biochemical profile was more affected by the growth phase than by the N source. Cellular contents of chlorophylls a and e decreased and the chlorophyll ale ratio increased when cultures entered the stationary phase. Protein and RNA were higher during exponential growth (about 30% and 8% ash free dry weight (AFDW), respectively), but carbo­ hydrates increased up to 220% in the stationary phase. Although significant differences were observed in cellular contents, the biochemical composition (as % AFDW) of the nitrate, nitrite and urea-grown cells was very similar. The highest total fatty acids and polyunsaturated fatty acids (PUFAs) contents in the stationary phase were obtained in the urea-grown cells, with an eicosapentaenoic acid (EPA) content of 26.8 mg.g- 1 of dry biomass.


Journal ArticleDOI
TL;DR: In this paper, the authors performed a large number of experiments under various conditions similar to those employed with apparent success by others, and the results suggest that the reported putative reaction does not occur.
Abstract: The reported heterogenous photocatalytic sythesis of NH 3 from N 2 and H 2 O in the presence of iron-doped TiO 2 or other semiconducting metal oxides has been investigated. Skepticism about this thermodynamically and mechanistically daunting process is appropriate, and the results reported here support a skeptical position. To assess the reproducibility of the results obtained by previous workers, we performed a large number of experiments under various conditions similar to those employed with apparent success by others. We also carried out 15 N isotope labelling experiments in which the lower limit of detection was around 0.2–1 nmol of added 15 NH 3 in 10 μmol of natural ammonia, i.e. two to three orders of magnitude below the levels reported in successful syntheses by others. All the catalysts tested promoted the photo-oxidation of ammonia under the conditions said to give ammonia photosynthesis. Photocatalytic nitrogen fixation was not found in any of the experiments, although in some cases results were obtained that could have been mistaken for nitrogen fixation. Our results suggest that the reported putative reaction does not occur. We recommend that any further research in this area should be based on standards of demonstration as rigorous as those applied in experiments on the biological fixation of nitrogen.

Journal ArticleDOI
TL;DR: In this article, the interaction of ammonia with (VO)2P2O7 prepared by calcination of the precursor compound VOHPO4·0.5H2O under nitrogen has been studied using temperature-programmed desorption of ammonia (TPDA), temperatureprogrammed reaction spectroscopy (TPRS), and IR and EPR spectroscopic analysis.
Abstract: The interaction of ammonia with (VO)2P2O7 prepared by calcination of the precursor compound VOHPO4· 0.5H2O under nitrogen has been studied using temperature-programmed desorption of ammonia (TPDA), temperature-programmed reaction spectroscopy (TPRS), and IR and EPR spectroscopy. Mass-spectrometric detection was applied to observe possible ammonia decomposition or oxidation products. The investigation revealed that ammonia is not only adsorbed on but also reacts with (VO)2P2O7 in a redox process generating nitrogen, water and an amorphous VIII-containing compound, the concentration of which could be directly determined by potentiometric titration. The high amount of VIII found pointed towards reduction of VIV not only on the surface but also in deeper layers of the bulk. This was also confirmed by EPR spectroscopy. Furthermore, this reaction results in a change of the Bronsted and Lewis acidity observed by IR spectroscopy. The concentration of the Bronsted-acid OH groups was strongly enhanced by hydrolysis of P—O—P and/or V—O—P links by water formed during the redox reaction. The increased concentration of Lewis sites was caused by the removal of oxygen from surface vanadyl groups, probably creating additional coordinatively unsaturated sites. The influence of the observed redox reaction on the characterization of the acidity and the formation of VPO catalysts in the ammoxidation reaction are discussed.

Journal Article
TL;DR: This study establishes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.
Abstract: BACKGROUND Ionized ammonia (NH3) transport in the intestine has not been previously established as a mechanism of acidosis in urinary intestinal diversion or hepatic failure. STUDY DESIGN The purpose of this study was to establish that ionized transport of ammonium (NH4) occurs in the intestine and to characterize the mechanism of its transport using the methodology of brush border membrane vesicles and acridine orange fluorescence. RESULTS An NH4/H exchange was demonstrated and found to be the dominant mechanism causing a pH change when NH4 is transported across the lumenal membrane. Ionized NH4 transport was demonstrated to occur against an NH3 concentration gradient. The Km was 1.02 mmol and the Vmax was 247 U/sec. The Hill coefficient was 0.97, indicating a single port. Ammonium hydrogen exchange could be inhibited by amiloride but not by bumetanide. Sodium, potassium or chloride, or both, did not effect the NH4/H exchanger. CONCLUSIONS This study establishes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.

Journal ArticleDOI
TL;DR: It is concluded that in sheep hepatocytes 15NH4Cl removal leads to quantitative formation of [15N2]urea, even in the presence of a physiological mixture of amino acids, supporting the concept of mitochondrial ammonia being in equilibrium with cytosolic aspartate formation.
Abstract: Ruminants characteristically absorb a large proportion of dietary nitrogen across the portal-drained viscera as ammonia nitrogen which is detoxified by conversion to urea in the liver. In theory, ammonia can supply both nitrogen atoms of the urea molecule via mitochondrial (carbamoyl phosphate) and cyto-plasmic (aspartate) precursor pathways of the ornithine cycle but the effect of amino acids on the flux of nitrogen from ammonia to each of the two urea nitrogen atoms has not been determined. We report a study designed to determine the distribution of [15N] ammonia between [15N1]urea and [15N2]urea in sheep hepatocytes in response to ammonia concentrations (0.33, 0.67 and 1.00 mM) in the presence or absence of amino acids. In the absence of amino acids, the enrichment of [15N2]urea rose more rapidly during incubations than [15N1]urea and attained enrichments of 66–88% within 5 min of incubation. At the end of 2.5 h of incubation, [15N2]urea represented 60% and 90% of the total urea molecules at low and high ammonia concentrations, respectively. The enrichments of glutamate and aspartate were similar to [15N1]urea in the cells at the end of the incubations, even in the presence of unlabelled amino acids, supporting the concept of mitochondrial ammonia being in equilibrium with cytosolic aspartate formation. In the presence of amino acids basal urea synthesis increased but ammonia uptake and 15NH4Cl conversion to urea was less than in the absence of amino acids. The rate of formation of [15N1]urea was greater in incubations containing amino acids but when ammonia concentration in the media was raised only [15N2]urea flux increased with no change in either [15N1]urea or the unlabelled species. Measurement of media amino acid concentrations after 2.5 h of incubation in the presence of amino acids revealed that arginine, glutamine, glycine and alanine were removed while there was net formation of aspartate, threo-nine, serine, glutamate, and the branched chain amino acids. However, less than 12% of the 15N transfer appeared in free amino acids. The increases in basal and unlabelled urea synthesis in the presence of amino acids could be numerically accounted as the sum of arginine and glutamine removal from incubations. It is concluded that in sheep hepatocytes 15NH4Cl removal leads to quantitative formation of [15N2]urea, even in the presence of a physiological mixture of amino acids. The increase in the formation of the [15N1]urea in the presence of amino acids can be explained by the preferential utilisation of the amide nitrogen of glutamine for urea synthesis.

Journal ArticleDOI
TL;DR: Saccharomyces cerevisiae was grown in a continuous culture at a single dilution rate with input ammonia concentrations whose effects ranged from nitrogen limitation to nitrogen excess and glucose limitation, and the governing factor of nitrogen metabolism might be the concentration of ammonia rather than its flux.
Abstract: Saccharomyces cerevisiae was grown in a continuous culture at a single dilution rate with input ammonia concentrations whose effects ranged from nitrogen limitation to nitrogen excess and glucose limitation. The rate of ammonia assimilation (in millimoles per gram of cells per hour) was approximately constant. Increased extracellular ammonia concentrations are correlated with increased intracellular glutamate and glutamine concentrations, increases in levels of NAD-dependent glutamate dehydrogenase activity and its mRNA (gene GDH2), and decreases in levels of NADPH-dependent glutamate dehydrogenase activity and its mRNA (gene GDH1), as well as decreases in the levels of mRNA for the amino acid permease-encoding genes GAP1 and PUT4. The governing factor of nitrogen metabolism might be the concentration of ammonia rather than its flux.

Journal ArticleDOI
TL;DR: In this article, the authors studied the mechanisms of thermal growth of silicon nitride films in ammonia using a resistance heated conventional furnace and a halogen lamp heated rapid thermal furnace, and the results indicated that the atomic transport through the growing nitride film occurs via nitrogenous species that include hydrogen.
Abstract: We studied the mechanisms of thermal growth of silicon nitride films in ammonia using a resistance heated conventional furnace and a halogen lamp heated rapid thermal furnace. The methods are based on isotopic tracing of nitrogen and hydrogen using different kinds of isotopically enriched ammonia for the thermal growth, 14 NH 3 , 15 NH 3 , and 14 ND 3 . The total amounts of the different isotopes were measured by nuclear reaction analyses. The nitrogen and hydrogen profiles were measured by either nuclear resonance depth profiling or nuclear reaction analyses associated with step-by-step chemical etching. A pronounced exchange between the hydrogen atoms on the silicon nitride films and those in the nitriding gas was observed, as well as an exchange of nitrogen atoms on a smaller scale. The results of the present investigation indicate that the atomic transport through the growing nitride film occurs via nitrogenous species that include hydrogen. The transport of silicon atoms or ions can also participate in the growth process, but they cannot be the only mobile species

Journal ArticleDOI
TL;DR: In this paper, the kinetics of de-esterification of high ester citrus pectin, using aqueous hydrochloric acid (HCl) solution or treatment with a mixture of ammonia in isopropanol were studied with respect to changes in methyl ester groups, molecular weight, and the formation of acid amide groups.

Journal ArticleDOI
TL;DR: In this paper, the simultaneous solubility of ammonia and carbon dioxide in aqueous solutions of sodium sulfate was measured in the temperature range 313--393 K at total pressures up to 3 MPa.
Abstract: The solubility of weak electrolyte gases such as ammonia, carbon dioxide, sulfur dioxide, or hydrogen cyanide must be known for process design in many applications. Typical examples are applications in the chemical and oil-related industries, the production of fertilizers, and applications in environmental protection. Correlating and predicting the simultaneous solubility of ammonia and sour gases in aqueous phases are difficult tasks due to chemical reactions in the liquid phase resulting in the presence of ionic species. Furthermore, the liquid phase often contains other strong electrolytes, and solid phases might precipitate. The simultaneous solubility of ammonia and carbon dioxide in aqueous solutions of sodium sulfate was measured in the temperature range 313--393 K at total pressures up to 3 MPa. Experimental results are reported and compared to correlations and predictions. Predicted results generally agree well with experimental data.


Patent
14 Sep 1995
TL;DR: In this article, a process for preparing low-chloride or chloride-free aminofunctional organosilanes by reacting chlorofunctionals with organic amines or ammonia and separating off the organic hydrochlorides or ammonium chloride was described.
Abstract: The present invention relates to a process for preparing low-chloride or chloride-free aminofunctional organosilanes by reacting chlorofunctional organosilanes with organic amines or ammonia and separating off the organic hydrochlorides or ammonium chloride thus formed, wherein further amounts of organic hydrochlorides or ammonium chloride present are reacted by addition of metal alkoxides dissolved in alcohols and the metal chlorides formed are separated off, and also to aminofunctional organosilanes prepared thereby.