Simulation of thermobaric conditions of the formation,composition, and structure of mixed hydrates containing xenon and nitrous oxide

Structural, dynamic, and thermodynamic features of double hydrates of xenon and nitrous oxide are calculated. Thermodynamic stability regions of these hydrates are found. At the atmospheric pressure the xenon hydrate is in the equilibrium with the gas phase at temperatures up to 263 K, whereas at these pressures the nitrous oxide hydrate decomposes already at 218 K. A strong dependence of the equilibrium temperatures and pressures of the formation/decomposition of double nitrous oxide and xenon hydrates on the composition of their mixture in the gas phase is shown.     

The activity of cobalt aluminum catalyst in reaction of nitrous oxide decomposition

Data of activity of cobalt aluminum catalysts with various content of active component in reaction of nitrous oxide decomposition obtained both on laboratory equipment and model catalytic reactor are presented.     

Treatment of off-gas evolved from thermal decomposition of sludge waste

Korea Atomic Energy Research Institute (KAERI) started a decommissioning program of a uranium conversion plant. The treatment of the sludge waste, which was generated during the operation of the plant, is one of the most important tasks in the decommissioning program of the plant. The major compounds of sludge waste are nitrate salts and uranium. The sludge waste is denitrated by thermal decomposition. The treatment of off-gas evolved from the thermal decomposition of nitrate salts in the sludge waste is investigated. The nitrate salts in the sludge were decomposed in two steps: the first decomposition is due to the ammonium nitrate, and the second is due to the sodium and calcium nitrate and calcium carbonate. The components of off-gas from the decomposition of ammonium nitrate at low temperature are NH₃, N₂O, NO₂, and NO. In addition, the components from the decomposition of sodium and calcium nitrate at high temperature are NO₂ and NO. Off-gas from the thermal decomposition is treated by the catalytic oxidation of ammonia and selective catalytic reduction (SCR). Ammonia is converted into nitrogen oxides through the oxidation catalyst and all nitrogen oxides are removed by SCR treatment besides nitrous oxide, which is greenhouse gas. An additional process is needed to remove nitrous oxide, and the feeding rate of ammonia in SCR should be controlled properly for evolved nitrogen oxides.     

Effect of NO, SO2, and O2 on the conversion of nitrous oxide on iron-containing zeolite catalysts

Conditions were found for facilitation of the conversion of nitrous oxide in the presence of Fe-containing zeolite catalysts by oxidants (NO, SO₂, and O₂). The results were interpreted in the framework of a mechanism involving decomposition of N₂O. The effect of NO_x on the reduction of nitrous oxide by C₃-C₄ alkanes was established. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 4, pp. 241–245, July–August, 2006.     

Infrared-induced reactivity of N2O on small gas-phase rhodium clusters

Far- and mid-infrared multiple photon dissociation spectroscopy has been employed to study both the structure and surface reactivity of isolated cationic rhodium clusters with surface-adsorbed nitrous oxide, Rh(n)N(2)O(+) (n = 4-8). Comparison of experimental spectra recorded using the argon atom tagging method with those calculated using density functional theory (DFT) reveals that the nitrous oxide is molecularly bound on the rhodium cluster via the terminal N-atom. Binding is thought to occur exclusively on atop sites with the rhodium clusters adopting close-packed structures. In related, but conceptually different experiments, infrared pumping of the vibrational modes corresponding with the normal modes of the adsorbed N(2)O has been observed to result in the decomposition of the N(2)O moiety and the production of oxide clusters. This cluster surface chemistry is observed for all cluster sizes studied except for n = 5. Plausible N(2)O decomposition mechanisms are given based on DFT calculations using exchange-correlation functionals. Similar experiments pumping the Rh-O stretch in Rh(n)ON(2)O(+) complexes, on which the same chemistry is observed, confirm the thermal nature of this reaction.     

Comprehensive DFT study of nitrous oxide decomposition over Fe-ZSM-5

The reaction mechanism for nitrous oxide decomposition has been studied on hydrated and dehydrated mononuclear iron sites in Fe-ZSM-5 using density functional theory. In total, 46 different surface species with different spin states (spin multiplicity M(S) = 4 or 6) and 63 elementary reactions were considered. Heats of adsorption, activation barriers, reaction rates, and minimum energy pathways were determined. The approximate minimum energy pathways and transition states were calculated using the "growing string method" and a modified "dimer method". Spin surface crossing (e.g., O(2) desorption) was considered. The minimum potential energy structure on the seam of two potential energy surfaces was determined with a multiplier penalty function algorithm by Powell and approximate rates of spin surface crossings were calculated. It was found that nitrous oxide decomposition is first order with respect to nitrous oxide concentration and zero order with respect to oxygen concentration. Water impurities in the gas stream have a strong inhibiting effect. In the concentration range of 1-100 ppb, the presence of water vapor influences the surface composition and the apparent rate coefficient. This is especially relevant in the temperature range of 600-700 K where most experimental kinetic studies are performed. Apparent activation barriers determined over this temperature range vary from 28.4 (1 ppb H(2)O) to 54.8 kcal/mol (100 ppb H(2)O). These results give an explanation why different research groups and different catalyst pretreatments often result in very different activation barriers and preexponential factors. Altogether perfect agreement with experimental results could be achieved.     

Formation of nitric oxide and nitrous oxide in electron-irradiated H(2)18O/N2 ice mixtures--evidence for the existence of free oxygen atoms in interstellar and solar system analog ices

We investigated the irradiation of low temperature H(2)(18)O/N(2) ice mixtures with energetic electrons in an ultrahigh vacuum chamber. The newly formed species, such as nitric oxide (N(18)O), nitrous oxide (NN(18)O), hydrogen peroxide (H(2)(18)O(2)) and hydrazine (N(2)H(4)), were identified in the experiments with infrared absorption spectroscopy and mass spectrometry. The results suggest that the unimolecular decomposition of water molecules within water ices at 10 K can lead to the formation of transient, suprathermal oxygen atoms. These oxygen atoms may play an important role in the formation of oxygen-containing biomolecules such as amino acids and sugar, as well as the decomposition of the biomolecules in the ices.     

Recent Advances in Catalytic Decomposition of N<Subscript>2</Subscript>O on Noble Metal and Metal Oxide Catalysts

Catalytic decomposition of nitrous oxide (N₂O) is one of the most efficient methods for the removal of N₂O which is of high greenhouse potential and ozone-depleting property. Recent progress in the decomposition of N₂O has been reviewed with the focus on noble meal and metal oxide catalysts. The influence factors, such as catalyst support, preparation method, alkali metal additives and the reaction conditions (including O₂, H₂O, SO₂, NO and CO₂), on the performance of deN₂O catalysts have been discussed. Finally, future research direction for the catalytic decomposition of N₂O is proposed.     

Influence of urea on initiation and termination of reaction between nitric acid and formic acid

The influence of urea on initiation and termination of the reaction between nitric and formic acids was experimentally examined. The urea injection can terminate the denitration reaction in 2 to 10M salt-free nitric acid solutions and the simulated high level liquid wastes (HLLWs) with a nitric acid concentration of 2 to 6M. An excess of urea can interrupt the initiation of denitration in both simulated HLLW and salt-free nitric acid solutions. The initiation and termination of denitration are in relation with nitrous acid formation and decomposition. Urea reacts with nitrous acid easily in the denitrating solution and decomposes nitrous acid. As the urea concentration increases in the solution, the continuance of denitration become impossible because the decomposition rate of nitrous acid exceeds the generation rate. In addition, the nitrous acid concentration can not be high enough to initiate the denitration in the solution with an excess of urea because nitrous acid is decomposed by urea.     

The effect of nitric oxide on the hydrogen-atom induced decomposition of monogermane

The effect of low concentrations of nitric oxide on the hydrogenatom initiated decompositton of monogermane at room temperature has been studied by a mass-spcctrometrtc technique. Initiation by hydrogen atoms, formed by mercury photosensitization of hydrogen-rich mixtures, insure the primayy decomposition path to be one forming germyl free radicals. The nitric oxide reacts efficienlly with germyl radicals thereby completely suppressing the normal formation of digermane until the nitric oxide concentration has been greatly reduced. The producss of the suppressonn reaction are digermylether (digermoxane), nitrous oxide, nitrogen and a solid containing germanium, hydrogen and oxygen. A mechanssm to account for these experimental facts is proposed and some of the rate constanss of the elementary chemical reactions have been estimaeed.     

Preparation of LaNiO3 perovskite by oxalate and carbonate precursor method for utilization as catalyst for high-temperature decomposition of N2O

The mixed oxide LaNiO₃ with perovskite structure was prepared by two relatively new and unconventional methods including preparation and thermal decomposition of mixed metal oxalate or carbonate precursors. The intermediates were prepared by reaction in a highly concentrated suspension (paste). The thermal decomposition conditions of these intermediates were described, and the final calcination temperatures were determined, which were done using thermal analysis methods and X-ray diffraction. During the decomposition of mixed carbonates, one-phase LaNiO₃ is produced directly, and in case of decomposition of oxalates, a mixture of LaNiO₃ and La₂O₃ is produced due to the formation of La₂O₂CO₃ during the heating. Catalytic decomposition of nitrous oxide at high temperature (650–930 °C) and high loading (GHSV?=?350,000 h^?1) has shown high LaNiO₃ activity, even at lower temperatures. The results were compared with the same compound obtained by co-precipitation and by solid-state reaction. Methods of preparation based on decomposition of oxalate and carbonate intermediates lead to the preparation of materials with appropriate composition, morphology, specific surface and high catalytic activity.

     

Oxidative dehydrogenation of propane by nitrous oxide and/or oxygen over Co beta zeolite

The oxidative dehydrogenation of propane has been studied with nitrous oxide (or mixture of nitrous oxide and oxygen) as oxidant. Nitrous oxide is a more selective but less active oxidant as compared with molecular oxygen. Upon increasing the concentration of N2O in the reaction mixture of propane and oxygen results in a substantial increase of propane conversion, while the selectivity to propene remains constant. The synergistic effect of O₂ and N₂O leads to a threefold higher yield of propene relative to than that of oxygen or nitrous alone. This revised version was published online in June 2006 with corrections to the Cover Date.     

P-Nitrosophosphate compounds: new N-O heterodienophiles and nitroxyl delivery agents

P-Nitrosophosphates, such as 9, react as N-O heterodienophiles with 1,3-dienes to form highly functionalized cycloadducts that can be directly transformed into allylic phosphoramidates. The in situ periodate oxidation of the unstable N-hydroxyphosphoramidate precursors provides an efficient preparation of these new reactive intermediates. P-Nitrosophosphate (9) regioselectively reacts with 1-methoxy-1,3-butadiene to provide cycloadduct 16. P-Nitrosophosphate (9) also reacts with 9,10-dimethylanthracene to give cycloadduct 17, which undergoes retro Diels-Alder dissociation to re-form 9. In the absence of a 1,3-diene, the decomposition of 17 produces nitrous oxide, evidence for nitroxyl, the one-electron-reduced form of nitric oxide. An asymmetric P-nitrosophosphate reacted with 1,3-cyclohexadiene to form a mixture of diastereomeric cycloadducts (19 and 20) in a 1.6:1 ratio. These results identify P-nitrosophosphates as new species that react similarly to acyl nitroso compounds, making them useful synthetic intermediates and potential nitroxyl delivery agents.     

The back-titration of chemisorbed atomic oxygen on copper by carbon monoxide investigated by microcalorimetry and transient kinetics

The back-titration of atomic oxygen chemisorbed on metallic copper using carbon monoxide is investigated by microcalorimetry. Results from simulations based on a microkinetic model of the back-titration are used for processing of microcalorimetric data. In addition, surface oxidation of copper by nitrous oxide is investigated by microcalorimetry. The results are compared with results obtained by nitrous oxide reactive frontal chromatography and by static oxygen adsorption studied by microcalorimetry. The heat of adsorption of nitrous oxide on copper amounts to 304 kJ mol⁻¹, and the heat of adsorption of carbon monoxide on surfaceoxidized copper is in the range from 120 to 70 kJ mol⁻¹.     

Interactions of nitrous oxide with fluorinated liquids

The interactions of nitrous oxide with fluorinated liquids are investigated by reporting original experimental results on gas solubility and interpreting them using molecular simulation. Nitrous oxide is highly soluble in the three fluorinated liquids studied-perfluorooctane, 1-bromoperfluorooctane (perfluorooctylbromide), and perfluorohexylethane-with mole fraction solubilities on the order of 0.03 under ambient conditions. An intermolecular potential model was developed for nitrous oxide, with a functional form of the Lennard-Jones plus point charges type, adjusted to the experimental multipole moments and to vapor-liquid equilibrium properties. The solubility of nitrous oxide in perfluorocarbon liquids was calculated by molecular simulation methods, and a dissimilar interaction parameter of 0.92 in the Lennard-Jones well-depths between solute and solvent had to be introduced to reach agreement with the experimental results, similar to what is found for hydrocarbon-fluorocarbon interactions. The structure of the solutions was studied by analysis of solute-solvent radial distribution functions, showing that, although electrostatic interactions are not predominant, a small orientational effect is still present between the dipole of nitrous oxide and those of the substituted fluorinated liquids.     

Microdetermination of nitrates and nitrites-III Gasometric and gravimetric methods based on reduction with formic acid

Simple microgasometric and gravimetric methods for the determination of the nitrate and nitrite groups are described. These are based on reduction with formic acid whereby one mole of nitrous oxide and four moles of carbon dioxide are simultaneously liberated per two moles of nitrate; two moles of nitrous oxide and six moles of carbon dioxide are liberated per seven moles of nitrite. Nitrous oxide is measured gasometrically and carbon dioxide gravimetrically. Results accurate to +/- 0.2% absolute are obtained for both nitrate and nitrite.     

Heterocyclic analogs of pleiadiene. XVII. Nitration of perimidines with nitrous acid and nitrogen dioxide

The corresponding nitroperimidines are formed instead of the expected nitroso compounds in the reaction of nitrous acid with perimidine and aceperimidine derivatives. Nitrogen oxides formed during the decomposition of nitrous acid are apparently the nitrating agent. In fact, nitrogen dioxide very readily nitrates perimidines and aceperimidines.     

Binding and Activation of N2O at Transition‐Metal Centers: Recent Mechanistic Insights

No laughing matter, nitrous oxide’s role in stratospheric ozone depletion and as a greenhouse gas has stimulated great interest in developing and understanding its decomposition, particularly through the use of transition‐metal promoters. Recent advances in our understanding of the reaction pathways for N₂O reduction by metal ions in the gas phase and in heterogeneous, homogeneous, and biological catalytic systems have provided provocative ideas about the structure and properties of metal N₂O adducts and derived intermediates. These ideas are likely to inform efforts to design more effective catalysts for N₂O remediation.     

不可一笑置之的笑气——一氧化二氮

一氧化二氮(N₂O)俗称“笑气”,是一种重要的氮氧化物。通过介绍N₂O的化学合成及其在合成化学中的应用、N₂O在人体内的作用机制及其医学应用以及人类活动排放N₂O所引发的全球环境问题,普及N₂O涉及的有关合成化学、生物化学和环境化学的基础知识。     

The pressure dependence of the thermal decomposition of N2O

The pressure dependence of the thermal decomposition of nitrous oxide was investigated behind shock waves at temperatures between 1570 K and 3100 K and pressures from 0.3 atm to 450 atm. Nitrous oxide concentration profiles were measured using IR emission from the 4.5-μm ν₁ band of N₂O. The pressure dependence of the measured rate constant was described using simple Lindemann fits, resulting in the following low- and high-pressure limiting rate coefficients: These values were used to extrapolate current measurements of the rate coefficient to lower temperatures, where the agreement with past work is excellent. Therefore the limiting rate coefficients given above should be suitable for kinetic modeling over a temperature range of 800–2000 K and pressures up to 450 atm. © 1996 John Wiley & Sons, Inc.