Removal of NO in NO/N2, NO/N2/O2, NO/CH4/N2, and NO/CH4/O2/N2 systems by flowing microwave discharges

In this paper, continuing previous work, we report on experiments carried out to investigate the removal of NO from simulated flue gas in nonthermal plasmas. The plasma-induced decomposition of small concentrations of NO in N2 used as the carrier gas and O2 and CH4 as minority components has been studied in a surface wave discharge induced with a surfatron launcher. The reaction products and efficiency have been monitored by mass spectrometry as a function of the composition of the mixture. NO is effectively decomposed into N2 and O2 even in the presence of O2, provided always that enough CH4 is also present in the mixture. Other majority products of the plasma reactions under these conditions are NH3, CO, and H2. In the absence of O2, decomposition of NO also occurs, although in that case HCN accompanies the other reaction products as a majority component. The plasma for the different reaction mixtures has been characterized by optical emission spectroscopy. Intermediate excited species of NO*, C*, CN*, NH*, and CH* have been monitored depending on the gas mixture. The type of species detected and their evolution with the gas composition are in agreement with the reaction products detected in each case. The observations by mass spectrometry and optical emission spectroscopy are in agreement with the kinetic reaction models available in literature for simple plasma reactions in simple reaction mixtures.     

Synthesis of O2'-methyluridine, O2'-methylcytidine, N4,O2'-dimethylcytidine and N4,N4,O2'-trimethylcytidine from a common intermediate

A facile synthesis of the title compounds from a readily accessible precursor, 3',5'-O-bis-protected O4-(2-nitrophenyl)uridine, is described.     

Ab initio calculations of nitrogen oxide reactions: formation of N2O2, N2O3, N2O4, N2O5, and N4O2 from NO, NO2, NO3, and N2O

Ab initio computational methods were used to obtain Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) for the reactions 2 NO <=> N(2)O(2) (I), NO+NO(2) <=> N(2)O(3) (II), 2 NO(2) <=> N(2)O(4) (III), NO(2)+NO(3) <=> N(2)O(5) (IV), and 2 N(2)O <=> N(4)O(2) (V) at 298.15 K. Optimized geometries and frequencies were obtained at the CCSD(T) level for all molecules except for NO, NO(2), and NO(3), for which UCCSD(T) was used. In all cases the aug-cc-pVDZ (avdz) basis set was employed. The electronic energies of all species were obtained from complete basis set extrapolations (to aug-cc-pV5Z) using five different extrapolation methods. The [U]CCSD(T)/avdz geometries and frequencies of the N(x)O(y) compounds are compared with literature values, and problems associated with the values and assignments of low-frequency modes are discussed. The standard entropies are compared with values cited in the NIST/JANAF tables [NIST-JANAF Thermochemical Tables, J. Phys. Chem. Ref. Data Monograph No. 9, 4th ed. edited by M. W. Chase, Jr. (American Chemical Society and American Institute of Physics, Woodbury, NY, 1988)]. With the exception of I, in which the dimer is weakly bound, and V, for which thermodynamic data appears to be lacking, the calculated standard thermodynamic functions of reaction are in good agreement with literature values obtained both from statistical mechanical and various equilibrium methods. A multireference-configuration interaction calculation (MRCI+Q) for I provides a D(e) value that is consistent with previous calculations. The combined uncertainties of the NIST/JANAF values for Delta(r)H(o), Delta(r)G(o), and Delta(r)S(o) of II, III, and IV are discussed. The potential surface for the dissociation of N(2)O(4) was explored using multireference methods. No evidence of a barrier to dissociation was found.     

Molecular Simulations of CO2/CH4, CO2/N2 and N2/CH4 Binary Mixed Hydrates

Colloid Journal - Grand canonical Monte Carlo simulations were performed to study the occupancy of structure I multicomponent gas hydrates by CO2/CH4, CO2/N2, and N2/CH4 binary gas mixtures with...     

Zur solvensfreien Darstellung von Tetramethylammoniumsalzen: Synthese und Charakterisierung von [N(CH3)4]2[C2O4], [N(CH3)4][CO3(CH3)], [N(CH3)4][NO2], [N(CH3)4][CO2H] und [N(CH3)4][O2C(CH2)2CO2(CH3)]

Solvent-free Synthesis of Tetramethylammonium Salts: Synthesis and Characterization of [N(CH₃)₄]₂[C₂O₄], [N(CH₃)₄][CO₃CH₃], [N(CH₃)₄][NO₂], [N(CH₃)₄][CO₂H], and [N(CH₃)₄][O₂C(CH₂)₂CO₂CH₃] A general procedure to synthesize tetramethylammonium salts is presented. Several tetramethylammonium salts were prepared in a crystalline state by solvent-free reaction of trimethylamine and different methyl compounds at mild conditions: [N(CH₃)₄]₂[C₂O₄] (cubic; a = 1 114.8(3) pm), [N(CH₃)₄][CO₃CH₃] (P2₁/n; a = 813.64(3), b = 953.36(3), c = 1 131.3(4) pm, β = 90.03(1)°), [N(CH₃)₄][NO₂] (Pmmn; a = 821.2(4), b = 746.5(3), c = 551.5(2) pm), [N(CH₃)₄][CO₂H] (Pmmn; a = 792.8(7), b = 791.7(3), c = 563.3(4) pm) and [N(CH₃)₄][O₂C(CH₂)₂CO₂CH₃] (P2₁; a = 731.1(2), b = 826.4(3), c = 1 025.2(3) pm, β = 110.1(1)°). The tetramethylammonium salts were characterized by IR-spectroscopy and X-ray diffraction. The crystal structures of the methylcarbonate and the nitrite are described.     

Stability of nitrogen-oxygen cages N12O2, N14O2, N14O3, and N16O4

Molecules consisting entirely of nitrogen have been studied extensively for their potential as high energy density materials (HEDM). However, many such molecules are too unstable to serve as practical energy sources. This has prompted many studies of molecules that are mostly nitrogen but which incorporate heteroatoms into the structure to provide additional stability. In the current study, cages of three-coordinate nitrogen are viewed as candidates for stabilization by insertion of oxygen atoms into the nitrogen framework. Cages of N12, N14, and N16 with four-membered rings are studied because four-membered rings have been previously shown to be a destabilizing influence. Insertion of oxygen atoms, which converts N-N bonds to N-O-N bonding groups, relieves ring strain and can potentially result in stable molecules. These molecules are studied by theoretical calculations, using Hartree-Fock and Moller-Plesset (MP3 and MP4) theories, to determine the dissociation energies of the molecules. The primary result of the study is that stable molecules can result from oxygen insertion but that oxygen-oxygen proximity destabilizes the insertion products.     

The sila-explosives Si(CH2N3)4 and Si(CH2ONO2)4: silicon analogues of the common explosives pentaerythrityl tetraazide, C(CH2N3)4, and Pentaerythritol Tetranitrate, C(CH2ONO2)4

The reaction of tetrakis(chloromethyl)silane, Si(CH2Cl)4, with sodium azide afforded tetrakis(azidomethyl)silane (sila-pentaerythrityl tetraazide, Si(CH2N3)4 (1b)). Nitration of tetrakis(hydroxymethyl)silane, Si(CH2OH)4, with nitric acid resulted in the formation of tetrakis(nitratomethyl)silane (sila-pentaerythritol tetranitrate, Si(CH2ONO2)4 (2b)). Compounds 1b and 2b are extremely shock-sensitive materials and very difficult to handle. Spectroscopic data were obtained as good as sensitivity and safety allowed for umambiguous identification. Quantum chemical calculations (DFT) of the C/Si pairs C(CH2OH)4/Si(CH2OH)4, 1a/1b, and 2a/2b regarding the structures and electronic populations were performed.     

Point charge models for LiH,CH4, and H2O

Point charge models for LiH. CH₄, and H₂O are presented. The models preserve the correct total charge and dipole moment of the molecules. Relations between spherical Gaussian wave function values and point charge model values of a variety of one-electron molecular properties are derived. The errors inherent in some of the point charge model values are of two types: those which may be large but are easily evaluated and those which are small and diminish rapidly as the distance from the molecule increases. The models are shown to be a reliable means of calculating one-electron properties and possible uses of the models are suggested.     

DMSO/N2H4.H2O/I2/H2O/CH3CN: a new system for selective oxidation of alcohols in hydrated media

A new alternative system for the oxidation of secondary alcohols to ketones with DMSO/N2H4.H2O/I2/H2O/CH3CN in hydrated media has been developed. The system also selectively oxidizes the secondary alcoholic groups to the corresponding ketones in the presence of primary alcoholic groups present within the same molecule in moderate to very good yields at reflux temperature.     

三通道气相色谱法监测大气中CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)北大核心CSCD

我国正处于“碳达峰、碳中和”的关键时期,准确认识我国温室气体浓度时空格局以及变化对于评估“碳达峰”和“碳中和”行动成效非常重要。当前我国近地面温室气体高精度监测主要依赖进口的光学监测主机,单台仪器成本高且监测要素有限。为此,该研究基于传统的气相色谱法,自主设计了一套三通道气相色谱分析系统,在单台仪器上实现了5种主要长寿命温室气体(CH_(4)、CO、CO_(2)、N_(2)O和SF_(6))的高精度监测。对该系统的精密度、线性响应情况和准确度进行的针对性测试实验表明系统检测性能满足世界气象组织/全球大气观测(WMO/GAW)质控标准。针对环境浓度的CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)的连续分析精密度分别达0.08%、1.90%、0.05%、0.08%、0.66%。准确度测试中,5种气体(CH_(4)、CO、CO_(2)、N_(2)O和SF_(6))使用回归方程计算所得值与标称摩尔分数间的偏差分别达0.15×10-9、0.20×10-9、0.37×10-6、0.35×10-9、0.02×10-12(摩尔分数),CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)仪器响应值与标称摩尔分数的线性拟合相关系数(R2)均为0.9999,线性拟合残差和准确度基本达到WMO/GAW拓展质控目标。该系统对杭州城区大气温室气体在线连续监测结果显示,2021年5~7月期间大气CH_(4)、CO、CO_(2)和N_(2)O呈明显的日变化特征,主要受人为活动影响。综合测试和试运行结果表明,该研发系统具备良好的精密度、准确度、线性和稳定性,与目前国内广泛进口的仪器相比,具有技术自主可控、运行成本更低、自动化水平更高等优势,能满足多种温室气体在线监测研究的需求。     

CH3COOH.TiO2: An excellent catalyst for the green nitration of toluene by N2O4

The solvent-free nitration of toluene with N₂O₄ gas over solid acid catalysts is a green reaction for preparing the mono-nitrotoluene (NT) isomers. The acid-modified catalysts are more efficient than common catalysts for this type of reaction. For this purpose, a titanium dioxide (TiO₂) catalyst is synthesized with a sol-gel method and modified by acetic acid to increase catalytic properties. The acid-modified TiO₂ (CH₃COOH·TiO₂) is characterized by different analyses. To optimization of toluene nitration conditions, reaction temperature (X₁) (30 < X₁ < 60 °C), N₂O₄/toluene molar ratio (X₂) (0.5 < X₂ < 2), and the amount of catalyst (X₃) (0.05 < X₃ < 0.3 g) factors were investigated by Minitab software with the CCD-RSM. Three responses including the selectivity of meta-NT isomer (S_m), the ratio of para-NT to ortho-NT selectivity (S_p/o), and the selectivity of by-products (S_bp) were considered for the optimization. Statistical parameters were applied to evaluate the goodness of fitting for the models. Optimum values for X₁, X₂, and X₃ parameters are 57.9 °C, 1.91, and 0.25 g, respectively. The conversion of toluene under these conditions is 93.2%. The comparison of S_m, S_p/o, and S_bp in CH₃COOH.TiO₂ (1.51%, 0.8, and 5.48%, respectively) with Fe₂O₃ (8.5%, 0.43, and 20.57%, respectively), SiO₂ (8.43%, 0.48, and 16.24%, respectively), TiO₂ (5.9%, 0.57, and 13.87%, respectively), TiO₂–Fe₂O₃ (4.72%, 0.64, and 9.18%, respectively), and TiO₂–SiO₂ (4.42%, 0.67, and 5.73%, respectively) catalysts show that this catalyst has a low S_m and S_bp as well as a higher S_p/o than other mentioned catalysts. The mechanism of the mentioned reaction is reviewed in the presence of CH₃COOH·TiO₂ catalyst. The high stability of the CH₃COOH·TiO₂ is proved by the reusability test, and it is found that its stability against inactivation is more than the TiO₂ catalyst.     

Gas-chromatographische Simultanbestimmung von O2, N2, CO,CO2, N2O,SO2, CH4, C2H4 und C2H6 im ppm-Bereich. I. Mitteilung

Zusammenfassung Die vorliegende Arbeit beschreibt ein neues Verfahren zur gas-chromatographischen Simultananalyse von N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ und C₂H₆ im Konzentrations-bereich von 10% bis 10 ppm ohne Voranreicherung. Die temperaturprogrammierte Trennung der Einzelkomponenten erfolgt nach Vorsäulensplitting auf zwei parallel geschalteten Säulen. Zur Emittlung der Retentionszeiten und der Peakflächen werden zwei voneinander unabhängige Ultraschalldetektoren verwendet, deren Analogsignale nach Digitalisierung in einem Mikrocomputer verarbeitet werden. Instrumentierung und chromatographische Einzelheiten werden beschrieben und diskutiert.

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Simultaneous gas chromatographic determination of N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ and C₂H₆ at the ppm-level. Part I

Summary A new procedure for the simultaneous determination of N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ and C₂H₆ by gas chromatography is described. Concentrations from 10% down to 10 ppm can be determined without preconcentration. After a pre-column splitting the individual compounds of the sample are separated by a uniform temperature program on two different columns in parallel. Detection of the effluents is achieved by two individual ultrasonic detectors, the data from which are processed in a micro-computer. Instrumentation and gas chromatographic details are described and discussed.

     

Heterogeneous interaction of N2O5 with HCl doped H2SO4 under stratospheric conditions: ClNO2 and Cl2 yields

The reaction of dinitrogen pentoxide, N2O5, with hydrogen chloride, HCl, in sulfuric acid solutions was studied at temperatures and compositions relevant to the upper troposphere/lower stratosphere. Experiments were performed using a rotating wetted wall flow tube reactor coupled to a chemical ionization mass spectrometer for the gas-phase detection of reactants (N2O5 and HCl) and products (nitryl chloride, ClNO2, and Cl2) using I– as the reagent ion. Uptake coefficients, γ, were measured under stratospheric conditions: 205 < T < 225 K; 50 and 60 wt % H2SO4 solutions; 5.8 × 10(–5) < [HCl]liq < 0.1 M. Uptake coefficients of N2O5 on pure H2SO4/H2O (50 and 60 wt % H2SO4) and HCl-doped H2SO4 were found to be independent of temperature and sulfuric acid composition (weight percent of H2SO4 and HCl concentration) consistent with previous studies. ClNO2 was observed to be a major gas-phase product with its yield strongly dependent on the liquid-phase HCl concentration (5.8 × 10(–5) to 0.1 M HCl) and with a maximum yield of nearly unity at 0.005 M HCl in both 50 and 60 wt % sulfuric acid solutions. The Cl2 yield was <1% under all conditions studied. ClNO2 production was attributed to the heterogeneous reaction of NO2(+)(aq), or H2NO3(+)(aq) (formed in the dissociative ionization of N2O5), with Cl–. The variation of the ClNO2 yield with HCl concentration was attributed to the competition between the reaction of NO2(+)(aq), or H2NO3(+)(aq) with Cl– and H2O. Using our measured yields as a function of HCl concentrations in 50 and 60 wt % H2SO4 solutions at different temperatures, we calculated the variation of the ClNO2 yield under stratospheric conditions. The atmospheric implications of these findings were examined using a 2D atmospheric model. The contribution of this chemistry to ozone depletion was found to be a minor process under nonvolcanic background aerosol levels.     

Ionization gauge sensitivities of N2, O2, N2O,NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^?1 Pa≤p≤1.3·10^?3Pa. Nitrogen was used as a calibration standard.     

Syntheses and Structures of S4N4(OCH3)2 and CH3OS4N4(O)Cl

The reaction of S₄N₄Cl₂ with CH₃OH gives S₄N₄(OCH₃)₂, a simple dimethoxoderivative of S₄N₄. Its overall geometry is analogous to other compounds of the S₄N₄X₂ type. The chlorination of S₄N₄(OCH₃)₂ leads to the oxidation of one sulfur atom to S^VI and CH₃OS₄N₄(O)Cl is formed. The compounds were characterized by ir spectroscopy and their crystal structures were determined from single crystal diffraction data collected at ?153°C. The presence of S^VI in the molecule of CH₃OS₄N₄(O)Cl is manifested by a marked shortening of the bonds formed by this atom as compared with S₄N₄Cl₂ and S₄N₄(OCH₃)₂.