含氮煤焦还原NO反应路径研究

采用量子化学密度泛函理论结合热力学和动力学分析研究了含氮煤焦还原NO的途径;从微观角度探究了含氮煤焦还原NO的间接还原和直接异相还原两种途径,分析了NO还原过程中的能量变化。结果表明,含氮煤焦先产生中间体NH_2再还原NO(间接还原)的过程决速步能垒值较直接异相还原NO的决速步能垒值高183.76 kJ/mol;由能垒角度分析,含氮煤焦与NO直接发生异相还原的过程更为有利。从热力学角度分析,含氮煤焦直接异相还原NO为可自发进行的单向放热反应,较间接还原过程有利。动力学分析结果表明,含氮煤焦间接还原NO的过程决速步速率常数较直接异相还原至少低10个数量级,说明含氮煤焦直接异相还原NO的路径更容易发生。     

苯硝化反应中电子转移反应重组能的计算

提出了重组能的量子化学算法,在用CISD/6-31G基组水平上,得到苯硝化反应中反应物及过渡态的结构.并计算了各自交换电子转移反应以及交叉电子转移反应的重组能,同实验重组能进行了比较.计算用了Gaussian 94程序.从重组能的角度分析了苯硝化反应.结果表明,对于NO2++NO2→NO2+NO2+的自交换电子转移反应,重组能较大,结论为: 在芳烃硝化反应中,存在以NO2+为氧化剂的电子转移步骤的可能性很小,而从动力学的角度上,用NO+作反应的氧化剂更有可能.     

MnZSM-5催化剂上NH3-SCR反应机理的研究

通过密度泛函理论（DFT）对Mn/ZSM-5催化剂上NH3-SCR反应机理进行了理论研究。一种为气态NO直接参与反应的E-R机理,NO分子与[NH2]反应生成中间体[NH2NO],该反应路径的能垒为43.35 kcal/mol;另一种为吸附态NO参与反应的L-H机理,[NO]与[NH3]反应生成[NH2NO],该反应路径的能垒为44.73 kcal/mol。因两种机理的反应能垒相差不大,因此在一定温度下遵循两种机理的反应皆能进行。     

由NO分子从头计算结果和紫外光电子能谱确定NO的分子结构

对于NO分子轨道的能级次序现有两种不同的说法,不少人根据NO与O_2~+是等电子体,由O_2~+分子的能级次序确定NO分子组态。本文用NO和O_2~(+)从头计算结果以及NO的紫外光电子能谱相结合的方法说明NO的5σ轨道是弱成键轨道,5σ的轨道能稍高于1π轨道能,也就是说NO的能级次序是与N_2分子相同的;NO与O_2~+虽是等电子体,但是能级次序并不相同,因此由O_2~+的能级次序确定NO分子的电子组态是不妥的。     

石墨炭负载单原子铁催化剂非均相还原NO的微观作用机理：DFT研究

基于密度泛函理论和经典过渡态理论,探究了石墨炭负载单原子Fe催化剂(Fe/G)异相还原NO的微观机理,并对催化剂失活原因进行分析。结果表明,基于E-R机理,NO还原反应依次经历了N₂O形成与释放、N₂形成与释放四个阶段。而基于L-H机理,NO还原反应主要经历了N₂形成与释放两个阶段。在E-R机理作用下,NO分子以N,O-down结构吸附在Fe原子上发生的NO还原反应的控速步骤能垒值仅为15.5 kJ/mol,小于其余路径控速步骤能垒值。由能垒角度分析,Fe原子上残留的活性氧被还原的能垒值高于NO还原生成N₂的能垒值。NO分解后残留在Fe原子表面的活性氧抑制了NO的吸附与还原,Fe原子活性位的缺失导致催化剂的失活,单原子Fe的存在促进了NO还原反应的进行。由动力学角度分析,随着反应温度的升高,NO还原速率较活性氧转移速率提升更为显著。     

硝基甲烷异构化反应势能面的ab initio研究

在B3LYP/6-311+ +G(2d,2p)水平上,优化得到硝基甲烷CH3NO2的10种异构体和23个异构化反应过渡态,并用G2MP2方法进行了单点能计算.根据计算得到的G2MP2相对能量,探讨了CH3NO2势能面上异构化反应的微观机理.研究表明,反应初始阶段的CH3NO2异构化过程具有较高的能垒,其中CH3NO2的两个主要异构化反应通道,即CH3NO2→CH3ONO和CH3NO2→CH2N(O)OH的活化能分别为270.3和267.8 kJ/mol,均高于CH3NO2的C-N键离解能.因而,从动力学角度考虑, CH3NO2的异构化反应较为不利.     

NO在Mn_2O_3(110)表面吸附的密度泛函理论研究

基于第一性原理密度泛函计算方法研究了NO在Mn_2O_3(110)面的吸附行为,计算了Mn_2O_3(110)面吸附NO和O_2的吸附构型的结构参数、吸附能和电子结构.结果表明,在Mn_2O_3(110)表面上,NO倾向于吸附在Mn top位,吸附前后的结构总能变化在-0.61~-1.29 eV之间,NO吸附后Mn吸附位周围的配位结构发生变化,使得Mn的电子向NO转移.进一步研究了吸附O_2后的Mn_2O_3表面再进一步吸附NO的行为,发现了ONOO*结构的形成.NO和O_2在表面共吸附形成ONOO*结构时的吸附能(-1.23和-1.39 eV)高于单纯吸附NO时的吸附能,此时Mn的电子向ONOO*结构转移,NO和O_2投影态密度的电子峰广泛交叠,说明成键原子之间有强共价键作用.     

N-亚硝基吲哚系列化合物及其自由基负离子在乙腈介质中N—NO键断裂能的测定

利用滴定量热技术并结合适当的热力学循环测定了乙腈溶液中7个取代的N-亚硝基吲哚化合物中N—NO键的异裂能和均裂能, 能量范围分别为206.1~246.2 kJ/mol和119.1~124.6 kJ/mol. 表明N-亚硝基吲哚均裂释放NO自由基(NO·)比异裂释放NO正离子(NO+)要容易得多, 通过热力学循环得到的相应自由基负离子中N—NO键的异裂能和均裂能的能量范围分别为25.5~34.4和5.0~40.5 kJ/mol, 表明所研究化合物的自由基负离子在室温下很不稳定.     

S-亚硝基-N-乙酰基-D,L-青霉胺二肽分子中S—NO键断裂能的测定

利用滴定量热技术并结合适当的热力学循环测定了乙腈溶液中7个S-亚硝基-N-乙酰基-D,L-青霉胺二肽化合物中S—NO键的异裂能和均裂能, 其能量范围分别为234.5—246.2 kJ/mol和101.6—122.1 kJ/mol. 结果表明, 所研究的亚硝基硫醇化合物更容易通过S—NO键的均裂释放NO自由基(NO·). 通过热力学循环对7个亚硝基硫醇化合物自由基负离子中S—NO键的异裂能和均裂能进行估算, 能量范围分别为19.2—35.5 kJ/mol和-4.2—22.6 kJ/mol, 表明这些自由基负离子在室温下不稳定, 容易通过S—NO键的异裂释放出NO-.     

Pt电极表面共吸附层NO和CO氧化还原的CV及原位FTIR研究

应用电化学循环伏安方法（CV）和原位傅里叶变换红外反射光谱（in situ FTIRS）研究了酸性溶液中Pt多晶电极表面NO和CO的共吸附行为及吸附态CO对吸附物种NO氧化还原反应的影响．研究结果表明,0．20V（VS．SCE）时,CO和NO能同时稳定吸附在Pt电极表面,CO以线性吸附态（CO L）存在,NO以桥式吸附态（NOB）和线性吸附态（NO L）共存．CO L 的共存使得NO的还原电流峰电位负移约0．024V,并且促使不易被氧化的NO B在0．93V处被氧化．原位FTIRS研究进一步表明,NO可以置换预吸附在电极表面的CO,NO和CO在Pt多晶电极表面的吸附是一个竞争吸附的过程．在0．45V-1．2V电位区间,NO和CO都能转化为环境友好产物,分别为NO3-和CO2．且Pt电极表面共吸附物种CO的量直接影响NO B的氧化产物NO3-的生成量．     

Determination of NO chemical affinities of benzyl nitrite in acetonitrile

There is an increasing interest in the study of NO chemical affinities of organic nitrites, for the biological and physiological effects of organic nitrites seem to be due to their ability to release NO. In this paper, NO chemical affinities of ten substituted benzyl nitrites were determined by titration calorimetry combined with a thermodynamic cycle in acetonitrile solution. The results show that ΔH _het(O-NO)s of benzyl nitrites are substantially larger than the corresponding ΔH _homo(O-NO)s, suggesting that these O-nitroso compounds much more easily release NO radicals by the O-NO bond homolytic cleavage. It is believed that the structural and energetic information disclosed in this work should be useful in understanding chemical and biological functions of organic nitrites. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(12): 2327–2329     

Cold-surface photochemistry of primary and tertiary alkyl nitrites

Reflection-absorption infrared spectroscopy (RAIRS) is used to explore the photochemistry of primary and tertiary alkyl nitrites deposited on a gold surface. The primary alkyl nitrites examined for this study were n-butyl, isobutyl, and isopentyl nitrite. These compounds showed qualitatively similar spectra to those observed in previous condensed-phase measurements. The photolysis of the primary nitrites involved the initial formation of an alkoxy radical and NO, followed by production of nitroxyl (HNO) and an aldehydic species. In addition, the formation of nitrous oxide, identified from its distinctive transition near 2230 cm(-1), was observed to form from the self-reaction of nitroxyl. The reaction rates for cis and trans conformer decay, as tracked through their intense N═O stretching modes, were found to be significantly different, potentially due to a structural bias that favors HNO formation for the initial trans conformer photoproducts over recombination. Tert-butyl nitrite demonstrates only the trans conformer in the RAIRS spectra prior to photolysis; however, recombination of the initial NO and RO(?) photoproducts was observed to produce the cis conformer in the photolyzed samples. The primary photoproducts from tert-butyl nitrite can also react to form acetone and nitrosomethane, but the absence of HNO prohibits the formation of N(2)O that was observed for the primary alkyl nitrites. Additionally, the RAIRS spectrum of isobutyl nitrite co-deposited with water was measured to examine the photolysis of this species on a water-ice surface. No change in the identity of the photoproducts was observed in this experiment, and minimal frequency shifting (1-3 cm(-1)) of the vibrational modes occurred. In addition to being a known atmospheric source of NO and various aldehydes, our results point to cold surface processing of alkyl nitrites as a potential environmental source of nitrous oxide.     

Reaction of nitric oxide at the beta-carbon of enamines. A new method of preparing compounds containing the diazeniumdiolate functional group

The reaction of nitric oxide (NO) with enamines has been investigated. Unlike previously reported reactions of NO as a free radical with alkenes, the electrophilic addition of NO to the beta-carbon of enamines results in the formation of compounds containing the diazeniumdiolate functional group (-[N(O)NO](-)). This reaction between NO and enamines has been shown to be quite general and a variety of enamine-derived diazeniumdiolates have been isolated and characterized. While enamines derived from aldehydes and ketones whose structures allow for sequential multiple electrophilic additions tended to undergo overreaction leading to unstable products, it has been shown that this complication may be overcome by suitable choice of reaction solvent. The products obtained may exist as zwitterionic iminium salts or as neutral species depending upon the structure of the parent enamine. The diazeniumdiolate derived from 1-(N-morpholino)cyclohexene is unique among the new compounds in that it spontaneously releases NO upon dissolution in buffered aqueous solution at pH 7.4 and 37 degrees C. While the total quantity of NO released by this material (ca. 7% of the theoretical 2 moles) is apparently limited by a competing reaction in which it hydrolyzes to an alpha-diazeniumdiolated carbonyl compound and the parent amine, this feature may prove to be of great value in the development of multiaction pharmaceuticals based upon this new type of NO-releasing compound. Reports of enzymatic (oxidative) release of NO from previously known carbon-bound diazeniumdiolates also suggest that analogues of these compounds may be useful as pharmaceutical agents. This new method of introducing the relatively rarely studied diazeniumdiolate functional group into organic compounds should lead to further research into its chemical and biological properties.     

NMR of Terminal Oxygen. Part 13. 17O-NMR spectra of C-nitroso compounds,thionitrites and NO+ Ion: Resonance effects in ON—X compounds and correlation with CD spectra

The ¹⁷O-NMR signals of four true C-nitroso compounds 1–4 appear at particularly low field (1550–1265 ppm), whereas the dimers (azodioxy type) resonate at ca. 400 ppm and the ‘isonitroso compounds’ ( ? quinone-oximes; 5 and 6 ) at ca. 250 ppm. S-Nitroso compounds ( ? thionitrites; 8 and 9 ) show shift values of ca. 1300 ppm, not far from C—NO; the NO⁺ ion is much stronger shielded (474 ppm). The results, together with those for higher-shielded nitroso compounds X—NO (X ? RO, R₂N, Cl, O^?) are discussed in terms of (a) resonance stabilization through n-donation from X(π-bond order, approximated by the known barriers of rotation around the X—N bond) and of (b) electronic excitation energies ΔE. The latter are approximated by long-wave (symmetry-forbidden) UV/VIS absorptions and confirmed, where available, by the maxima of the curves of circular dichroism (CD); the CD curve of thionitrite 9 has been measured. It is found that the δ(¹⁷O) values of X—NO depend both on bond order and on ΔE, which could not be separated. The higher shielding of NO⁺ compared with X—N?O is explained on the basis of anisotropy effects, which differ between sp and sp² systems.     

Negative ion chemical ionization mass spectrometry of some nitroso compounds with CO2 as reagent gas

Summary Mass spectra of seven N-nitrosamines and five alkyl nitrites, the O-nitroso compounds, have been obtained by low pressure negative chemical ionization with CO₂ as reagent gas. Intense anions were observed at m/z M–32 for N-nitrosamines and at m/z M–30 for alkyl nitrites. Addition products were found at m/z M+12 and M+43 for N-nitrosamines and at m/z M+14 for alkyl nitrites. By using isotopically labeled CO₂, it could be shown that the anions at m/z M+12, M+14 and M+43 correspond to [M - H₂NO + CO₂ ^–, [M – NO + CO₂]^–, and [M – H + CO₂]^–, respectively.

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Negativionen-CI-Massenspektrometrie einiger Nitrosoverbindungen mit CO₂ als Reagensgas

Zusammenfassung Die Massenspektren von sieben N-Nitrosaminen und fünf Alkylnitriten (O-Nitrosoverbindungen) wurden durch negative chemische Ionisation bei niederem Druck mit CO₂ als Reagensgas erhalten. Intensive Anionen wurden bei m/z M–32 für N-Nitrosamine und bei m/z M–30 für Alkylnitrite beobachtet. Additionsprodukte fanden sich bei m/z M+12 und M+43 für N-Nitrosamine sowie bei m/z M+14 für Alkylnitrite. Mit Hilfe von Isotopen-markiertem CO₂ konnte gezeigt werden, daß die Anionen bei m/z M+12, M+14 und M+43, [M – H₂NO + CO₂]^–, [M – NO + CO₂]^– bzw. [M – H + CO₂]^– entsprechen.

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A full account of this work including the negative chemical ionization mass spectra obtained with other reagent gases will be submitted to the Journal of Mass Spectrometry.     

Selective catalytic reduction of NO by propane over CoO(x)/Al2O3: an investigation of the surface reactions using in situ infrared spectroscopy

The partial oxidation of propane and the mechanism of the selective catalytic reduction (SCR) of NO by C3H8 over CoO(x)/Al2O3 catalysts were investigated using in situ infrared spectroscopy. Emphases are placed on the formation and reactivity of surface oxygenates during the SCR reaction. The SCR reaction starts with partial oxidation of propane to adsorbed acetate and formate. Impregnation of cobalt onto alumina greatly enhanced this reaction. The as-formed acetate acts as an efficient reductant for NO reduction. Surface nitrates (nitrites) are also reactive to propane and to oxygenates generated from C3H8 + O2 reaction. Surface -NCO species are formed over CoO(x)/Al2O3 catalysts. These nitrogen containing organic species are believed to be the direct intermediates in the final formation of N2. On the basis of these investigations, a proposed reaction mechanism explains the formation and roles of all intermediates detected by IR spectroscopy in this study.     

Electrochemical determination of nitric oxide and of its derivatives

Nitric oxide (NO) is one of the simplest odd electron species. Furthermore, it is relatively hydrophobic, which is consistent with its role as a diffusible intracellular messenger or as an immune effector. NO is generated in biological systems and plays important roles as a regulatory molecule. The main problem in NO analysis is its extreme reactivity; in aerated water solution it is transformed into nitrite and nitrate, inactive biological forms. Moreover, it may lose an electron forming the NO⁺ ion, involved in the synthesis of nitrosothiols (RSNOs). The main problems encountered in the analytical determination of free NO and of RSNOs in biological systems are the low stability and the very low concentration of these compounds. The determination of nitrates and nitrites may also be difficult when their concentration is in the nmolar range. We describe an electrochemical assay for the determination in the same sample of free NO and of its derivatives in nmolar range. Owing to its high sensitivity, the procedure could also be applied to environmental analyses     

PCM study of the solvent and substituent effects on bond dissociation energies of the O?NO Bond—A DFT study

A PCM continuum model, at the B3LYP, B3P86, and B3PW91 three‐parameter hybrid DFT methods with 6‐311G** basis set, is used to study the bond dissociation energies (BDEs) of benzyl nitrites. Compared the computed results with the experimental values, it is noted that B3PW91 functional is the best method to compute the BDEs of benzyl nitrites. The solvent and substituent effects on the BDEs of the O? NO bond are analyzed, and it is shown that the BDE of the O? NO bond decreases with the increment of the Hammett constants of substituent groups on benzene for benzyl nitrites except C₆H₅CH₂O? NO. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Analysis of chemical kinetics at the gas-aqueous interface for submicron aerosols

The effect of kinetics of chemical reactions in the gas-liquid interface between atmospheric gases and reactive solute in dilute aqueous aerosols is analysed in order to see if such processes will affect the overall uptake rate. Accordingly, a parameterization of such heterogeneous reactions was derived, taking into account interfacial reactions. Gibbs surface excess concentration of both reactive compounds and stable compounds leads to higher heterogeneous reaction rates in comparison to aqueous phase bulk reactions. An analytical formulation shows that the surface reactions may be of considerable importance for the uptake process in the case of small liquid aerosols even in the absence of organic film on the surface. In particular, we demonstrate that the uptake rate of atmospheric gas-phase oxidants (such as OH, NO(3) or O(3)) reacting with volatile organic compounds (such as ethanol or methanol) is increased by more than 10% for atmospheric aerosols with diameters lower than 0.1 microm. This effect is in addition intensified in the case of reactions of atmospheric oxidants with liquid aerosols containing organic surfactants, such as semi-volatile organic compounds, i.e., the chemical reactions at the gas-liquid interface may be dominant in the main uptake process for atmospheric submicron aerosols.     

17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

The ozone molecule possesses a unique and distinctive (17)O excess (Δ(17)O), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO(2) + O(3) reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Δ(17)O from ozone to nitrate radical (NO(3)) during the gas-phase NO(2) + O(3) → NO(3) + O(2) reaction was investigated in a series of laboratory experiments. The isotopic composition (δ(17)O, δ(18)O) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Δ(17)O transfer function for the NO(2) + O(3) reaction was determined to be: Δ(17)O(O(3)?) = (1.23 ± 0.19) × Δ(17)O(O(3))(bulk) + (9.02 ± 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Δ(17)O values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen.