Showing papers on "Ammonia published in 2004"

Hydrogenation and cleavage of dinitrogen to ammonia with a zirconium complex

Abstract: Molecular nitrogen is relatively inert owing to the strength of its triple bond, nonpolarity and high ionization potential. As a result, the fixation of atmospheric nitrogen to ammonia under mild conditions has remained a challenge to chemists for more than a century. Although the Haber–Bosch process produces over 100 million tons of ammonia annually1 for the chemical industry and agriculture2, it requires high temperature and pressure, in addition to a catalyst3, to induce the combination of hydrogen (H2) and nitrogen (N2). Coordination of molecular nitrogen to transition metal complexes can activate and even rupture the strong N–N bond4 under mild conditions, with protonation yielding ammonia in stoichiometric5 and even catalytic yields6. But the assembly of N–H bonds directly from H2 and N2 remains challenging: adding H2 to a metal–N2 complex results in the formation of N2 and metal–hydrogen bonds or, in the case of one zirconium complex7, in formation of one N–H bond and a bridging hydride. Here we extend our work on zirconium complexes containing cyclopentadienyl ligands8,9 and show that adjustment of the ligands allows direct observation of N–H bond formation from N2 and H2. Subsequent warming of the complex cleaves the N–N bond at 45 °C, and continued hydrogenation at 85 °C results in complete fixation to ammonia.

Application of real-time PCR to study effects of ammonium on population size of ammonia-oxidizing bacteria in soil.

Abstract: limit of 1.3 10 5 cells/g of dry soil. The effect of the ammonium concentration on AOB population density was measured in soil microcosms by applying 0, 1.5, or 7.5 mM ammonium sulfate. AOB population size and ammonium and nitrate concentrations were monitored for 28 days after (NH4)2SO4 application. AOB populations in amended treatments increased from an initial density of approximately 4 10 6 cells/g of dry soil to peak values (day 7) of 35 10 6 and 66 10 6 cells/g of dry soil in the 1.5 and 7.5 mM treatments, respectively. The population size of total bacteria (quantified by real-time PCR with a universal bacterial probe) remained between 0.7 10 9 and 2.2 10 9 cells/g of soil, regardless of the ammonia concentration. A fertilization experiment was conducted in a tomato field plot to test whether the changes in AOB density observed in microcosms could also be detected in the field. AOB population size increased from 8.9 10 6 to 38.0 10 6 cells/g of soil by day 39. Generation times were 28 and 52 h in the 1.5 and 7.5 mM treatments, respectively, in the microcosm experiment and 373 h in the ammonium treatment in the field study. Estimated oxidation rates per cell ranged initially from 0.5 to 25.0 fmol of NH4 h 1 cell 1 and decreased with time in both microcosms and the field. Growth yields were 5.6 10 6 , 17.5 10 6 , and 1.7 10 6 cells/mol of NH4 in the 1.5 and 7.5 mM microcosm treatments and the field study, respectively. In a second field experiment, AOB population size was significantly greater in annually fertilized versus unfertilized soil, even though the last ammonium application occurred 8 months prior to measurement, suggesting a long-term effect of ammonium fertilization on AOB population size. Ammonium oxidation by autotrophic ammonia-oxidizing bacteria (AOB) is a key process in agricultural and natural ecosystems, with a large global impact. The product of this process, nitrite, is immediately oxidized by nitrite-oxidizing bacteria to nitrate, a nitrogen form susceptible to leaching. Nitrogen leaching can lead to groundwater pollution and sur

Aqua ammonia process for simultaneous removal of CO2, SO2 and NOx

Abstract: Experimental research work in applying aqueous ammonia solution for the simultaneous reduction of acidic gaseous emission from fossil fuel-fired utility plants is currently being performed at the National Energy Technology Laboratory. The traditional monoethanolamine process for CO2 removal suffers the disadvantages of low carbon dioxide loading capacity, equipment corrosion, amine degradation by SO2 and O2 in flue gas, and high energy penalty during absorbent regeneration. The aqueous ammonia process can simultaneously remove CO2, SO2, NOx, plus HCl and HF that may exist in the flue gas. There could be oxidation of SO2 and NO prior to contacting the aqueous ammonia absorbent. Test results pertaining to the ammonia/carbon dioxide reaction in a semi-continuous reactor system are presented. The parametric effects of sparger design, reaction temperature, and ammonia concentration on gas loadings and absorption rates are discussed. Regeneration test results, including solution-cycling between the regeneration and absorption steps to determine a realistic loading capacity for the ammonia solutions are also presented.

Chlorination byproduct formation in the presence of humic acid, model nitrogenous organic compounds, ammonia, and bromide.

Abstract: The formation of trihalomethanes (THMs), haloacetic acids (HAAs), and cyanogen halides (CNXs) after chlorination of synthetic solutions containing humic acid, nitrogenous organic (N-organic) compounds, ammonia, and bromide ions was studied. Humic acid (from Aldrich) was used to provide the source of the precursors. Glycine was chosen as the primary model N-organic compound and other four model N-organic compounds (including glutamic acid, glycylglycine, diethylamine, and methylamine) were also evaluated for comparison. The formation of THMs and HAAs was found to decrease with increasing glycine and ammonia concentrations but to increase with increasing bromide ion concentration. CNX formation was found to be highly sensitive to free chlorine to glycine ratios, and its formation trends were significantly affected by the presence/absence of ammonia. The incorporation of bromine changed the byproducts speciation toward brominated species and enhanced the yields of total THMs, HAAs, and CNXs. Different model ...

An FT-IR study of the adsorption and oxidation of N-containing compounds over Fe2O3/Al2O3 SCR catalysts

Abstract: The interaction of NO, ammonia (NH3), hydrazine (N2H4) and hydroxylamine (NH2OH) on Fe2O3/Al2O3 model catalyst was studied. The data support the idea that hydrazine can be intermediate in the oxidation of ammonia to nitrogen, while hydroxylamine-type species, can be intermediate in the oxidation of ammonia to NO. On the contrary to those observed over Fe2O3/TiO2 previously studied, hydroxylamine-type species are formed at relatively low temperature, indicating that Fe2O3/Al2O3 is less selective in SCR reaction with ammonia.

Ozonation of naphthalenesulphonic acid in the aqueous phase in the presence of basic activated carbons.

Abstract: The present study aimed to explore the possibility of increasing the purification efficacy of ozone in the removal of high-toxicity contaminants by using carbons of basic character and to analyze the mechanism involved in this process. These carbons were prepared by treating a commercial activated carbon (Witco, W) with ammonia (W−A), ammonium carbonate (W−C), or urea (W−U), under high pressure and temperature. The ammonia and carbonate treatments slightly increased the mesoporosity and, to a greater degree, the macroporosity of carbon W, whereas the urea treatment produced an increase in the porosity across the whole range of pore sizes. In addition, treatment of the activated carbon with these nitrogenating agents produced a marked change in the chemical nature of its surface. Thus, according to the pH of the point of zero charge (pHPZC) values obtained for each sample, carbon W was neutral (pHPZC = 7.12), but the treated carbons were basic, especially carbon W−U (pHPZC = 8.85). This basicity results fr...

Investigation of ammonia removal from polluted waters by Clinoptilolite zeolite

Abstract: Ammonia nitrogen compounds in the wastewaters and effluents have harmful effects on water resources. Ion exchange with zeolites is a separation process for ammonia removal from effluents. The objective of this research was to study the efficiency of an ammonia removal and the factor affecting to this process. The Clinoptilolite was obtained from Semnan mines at the north part of Iran. The samples were grounded and sieved based on the U.S. standard mesh number 20, 30, 40 and conditioned by ammonia sulfate and sodium chloride solutions. The characteristics of samples for ammonia removal and the selectivity sequence for adsorbing interfering cations were then determined. Results shown that the average ion exchange capacity of zeolite in batch and continuous systems were 6.65–16 and 16.31–19.5 mg NH4 + /g zeolite weight, respectively. In study on the zeolite for selective cations showed the ranking of K+, NH4 +, Na+, Ca2+ and Mg2+ respectively. Results indicated that high level of regeneration (95–98%) might be achieved with NaCl solution. Based on the results, Clinoptilolite may be effective applied in wastewater treatment, both from technical and economical aspects.

Supercritical water oxidation of phenol and 2,4-dinitrophenol

Abstract: The oxidation of high concentrations of phenol and 2,4-dinitrophenol (DNP) was investigated in a pilot-scale supercritical water oxidation (SCWO) system. Treatment for approximately 40 s at a pressure of 25 MPa, temperatures of 666–778 K and oxygen excess of 0–34%, resulted in phenol destruction from 94 to 99.98%, consistent with extrapolations of some global rate laws proposed in the literature. Destruction of total organic carbon (TOC) varied from 75 to 99.77%. Two different solutions that contained DNP were studied following the phenol experiments. The first solution contains 2.4 wt.% of 2,4-DNP with 2.1 wt.% of ammonium sulphate. Treatment at under 43 s at 25 MPa, 780 K with a large oxygen excess, resulted in destruction efficiencies of over 99.9996% for DNP and 99.92% for TOC. Mono-nitrophenols were detected as intermediates, but not in the final effluent, where residuals of ammonium bicarbonate and sulphates were detected. This solution was extremely corrosive to the Alloy 625 preheaters at temperatures of approximately 370 °C. The second solution contained 2.26 wt.% of 2,4-DNP, with ammonia but no sulphates and was treated at 24.5 MPa, 742–813 K and oxygen concentrations ranging from sub-stoichiometric to 67% excess. Destruction efficiencies for 2,4-dinitrophenol were over 99.9996% in all cases. TOC destruction efficiencies ranged from 98.98 to 99.98%, while ammonia destruction ranged from 15 to 50%. Picric acid and mono-nitrophenols were detected as intermediates, but not in the liquid effluent. No CO or NOx was present in the effluent gas samples, except in cases with less than stoichiometric oxygen.

Electrocatalytic reduction of nitrate on activated rhodium electrode surfaces

Abstract: Electrodeposited rhodium films on titanium substrates have been electrochemically activated to produce a high area surface with a specific activity for nitrate electroreduction directly to N2. The activation process involves oxidation/reduction cycles in an alkaline, KCl electrolyte containing nitrate ions. Surfaces of up to 230 times the geometric area are achieved, together with a surface morphological modification. While the active surface, once formed, is intrinsically unstable during long-term nitrate reduction, its activity can be maintained in situ by an electrochemical cycling procedure. The high area rhodium has the form of a nano-structured ‘sponge’, with a surface area of ca. 19 m2 g−1. The morphological modification is evidenced by a change in the hydrogen UPD structure, changes in the surface redox behaviour associated with OH adsorption, and a reduction in the activation energy for nitrate reduction from ca. 47 to 20 kJ mol−1. The reduction in activation energy, however, is accompanied by a decrease in the pre-exponential factor, and this apparent compensation effect results in similar rate constants on the activated and unactivated surfaces. The enhancement in the catalyst's activity for nitrate reduction results from an increase in the relative activity of nitrate reduction over water reduction. The activated catalyst sustains steady state nitrate reduction at an increased over-potential before the reaction to N2 decays, and hydrogen evolution and reduction to ammonia take place. The presence of nitrate ions is essential for the formation of the active surface, and specifically adsorbed nitrate ions and reductive intermediates are present at the surface when it is reformed. A mechanism for the elementary surface reaction steps involved in nitrate reduction, and the apparent ‘habit’ growth of the active surface phase in the nitrate containing solution is discussed.

Toxicological profile for ammonia

Abstract: DISCLAIMER The use of company or product name(s) is for identification only and does not imply endorsement by the Agency for Toxic Substances and Disease Registry. vi AMMONIA *Legislative Background The toxicological profiles are developed in response to the Superfund Amendments and Reauthorization Act (SARA) of 1986 (Public law 99-499) which amended the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA or Superfund). This public law directed ATSDR to prepare toxicological profiles for hazardous substances most commonly found at facilities on the CERCLA National Priorities List and that pose the most significant potential threat to human health, as determined by ATSDR and the EPA. The availability of the revised priority list of 275 hazardous substances was announced in the to prepare a toxicological profile for each substance on the list. Toxicological Profiles are a unique compilation of toxicological information on a given hazardous substance. Each profile reflects a comprehensive and extensive evaluation, summary, and interpretation of available toxicologic and epidemiologic information on a substance. Health care providers treating patients potentially exposed to hazardous substances will find the following information helpful for fast answers to often-asked questions. Chapter 1: Public Health Statement: The Public Health Statement can be a useful tool for educating patients about possible exposure to a hazardous substance. It explains a substance's relevant toxicologic properties in a nontechnical, question-and-answer format, and it includes a review of the general health effects observed following exposure. Chapter 3: Health Effects: Specific health effects of a given hazardous compound are reported by type of health effect (death, systemic, immunologic, reproductive), by route of exposure, and by length of exposure (acute, intermediate, and chronic). In addition, both human and animal studies are reported in this section. NOTE: Not all health effects reported in this section are necessarily observed in the clinical setting. Please refer to the Public Health Statement to identify general health effects observed following exposure. The following additional material can be ordered through the ATSDR Information Center: Case Studies in Environmental Medicine: Taking an Exposure History—The importance of taking an exposure history and how to conduct one are described, and an example of a thorough exposure history is provided. Other case studies of interest include Reproductive and Developmental viii AMMONIA Hazards; Skin Lesions and Environmental Exposures; Cholinesterase-Inhibiting Pesticide Toxicity; and numerous chemical-specific case studies. Managing Hazardous Materials Incidents is a three-volume set of recommendations for on-scene (prehospital) and hospital …

Electro-catalysts for the oxidation of ammonia in alkaline media

Abstract: An electro-catalyst for the oxidation of ammonia in alkaline media; the electrocatalyst being a noble metal co-deposited on a support with one or more other metals that are active to ammonia oxidation. In some embodiments, the support is platinum, gold, tantalum, or iridium. In some embodiments, the support has a layer of Raney metal deposited thereon prior to the deposition of the catalyst. Also provided are electrodes having the electro-catalyst deposited thereon, ammonia electrolytic cells, ammonia fuel cells, ammonia sensors, and a method for removing ammonia contaminants from a contaminated effluent.

Ammonium and hydroxylamine uptake and accumulation in Nitrosomonas

Abstract: Starved cells of Nitrosomonas europaea and further ammonia oxidizers were able to rapidly accumulate ammonium and hydroxylamine to an internal concentration of about 1 and 0·8 M, respectively. In kinetic studies, the uptake/accumulation rates for ammonium [3·1 mmol (g protein)−1 min−1] and hydroxylamine [4·39 mmol (g protein)−1 min−1] were determined. The uptake and accumulation process of ammonium and hydroxylamine was not coupled to ammonia or hydroxylamine oxidation and nitrite was not produced. In the presence of uncouplers the ammonium accumulation was completely inhibited, indicating an active, membrane-potential-driven transport mechanism. When the external ammonium or hydroxylamine pool was depleted, the internal ammonium and hydroxylamine was consumed within 12 h or 20 min, respectively. The binding of ammonium/ammonia was correlated with an energized membrane system, and hydroxylamine may bind to the hydroxylamine oxidoredutase.

Combustion of methane over palladium catalyst in the presence of inorganic compounds: inhibition and deactivation phenomena

Abstract: The influence of the presence of different inorganic gases, often found in methane-containing industrial off-gases (NH3, NO2, H2, H2O, SO2, H2S, CO and CO2) on the catalytic combustion of methane over a Pd/Al2O3 catalyst is studied in the present work, in a range of concentrations corresponding to typical industrial emissions, such as those of coke oven facilities. Results show that the effect of SO2 and H2S on the catalyst is similar, both compounds causing partially irreversible poisoning, whereas water (present in the feed or formed by combustion of H2 or CH4) causes reversible inhibition in the absence of sulphur compounds. Nitrogen-containing compounds increase methane conversion in the absence of sulphur-containing compounds, but ammonia has the opposite effect when sulphur compounds are present. The other compounds studied do not affect appreciably the catalytic combustion of methane.

Ammonia Absorption on Alkaline Earth Halides as Ammonia Separation and Storage Procedure

Abstract: For the low pressure ammonia synthesis (∼1 MPa, 573–623 K), 40–80 kPa of ammonia produced must be separated. For this purpose, the absorption behavior of five kinds of alkaline earth metal halides ...