煤炭解耦燃烧过程N迁移与转化Ⅱ:单组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N₂O的还原实验研究,考察了反应温度、过剩空气系数λ、热解气中CH₄、CO、H₂、NH₃浓度、烟气中NO、N₂O浓度变化对NO、N₂O出口浓度的影响。实验结果表明,当模拟热解气仅含其中一种气体时,在反应温度973~1 223 K时热解气中CH₄、CO、H₂基本不与NO发生反应,当λ小于或等于1.0时可降低N₂O浓度0%~30%;热解气中NH₃可降低NO 10%~60%,但NH₃不与N₂O发生反应。     

煤炭解耦燃烧过程N迁移与转化Ⅲ:多组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N₂O的还原实验研究,考察了反应温度、过剩空气系数,模拟热解气中CH₄、CO、H₂、NH₃入口浓度与模拟烟气中NO、N₂O入口浓度对NO、N₂O与总氮转化率的影响。结果表明,向NH₃添加可燃气体CO、H₂、CH₄可使NO还原窗口向低温方向移动150~200 K,该温度窗口为1 073~1 223 K;但NH₃-CO-H₂-CH₄-O₂体系对NO、N₂O的还原分解作用依赖于体系的O₂浓度,仅在富燃料情形(过剩空气系数λ为0.6)下可分别达60.6%、100%的NO、N₂O脱除率;在反应温度1 073~1 223 K及过剩空气系数λ为0.6条件下,较高的热解气CH₄、CO、H₂浓度可增加NO排放,但有利于还原N₂O;增加NH₃入口浓度可增加NO分解率。     

Nitrous oxide gas phase chemistry during silicon oxynitride film growth

N₂O gas phase chemistry has been examined as it relates to the problem of ultrathin film silicon oxynitridation for semiconductor devices. Computational and analytical kinetics studies are presented that demonstrate: (i) there are 5 main reactions in the decomposition of N₂O, (ii) the gas composition over a 1000K – 1400K temperature range is as follows: N₂ (65.3 − 59.3%); O₂ (32.0 − 25.7%); NO (2.7 − 15.0%), (iii) the N₂O decomposition obeys first-order kinetics, and the initial rate law for N₂O decomposition is R_init = 2k₁[N₂O] which rapidly changes to R_late = k₁[N₂O] as the reaction proceeds, (iv) the branching ratio for the two reactions: N₂O + O → 2NO and N₂O + O → N₂ + O₂ lies between 0.1 and 0.5 (0.1 < < 0.5) and varies with conditions, (v) the apparent activation energy for the decomposition of N₂O is 2.5 eV/molecule (2.4×10² kJ/mole), (vi) the rate law for NO formation is R = k₁N₂O], and (vii) the apparent activation energy for the formation of NO is 2.4 eV/molecule (2.3×10² kJ/mole).     

N2O emission in partial nitritation-anammox process

Nitrous oxide(N2O)is one of the significant greenhouse gases,and partial nitritation-anammox(PNA)process emits higher N2O than traditional nitrogen removal processes.N2O production in PNA mainly occurs in three different pathways,i.e.,the ammonia oxidizing bacteria(AOB)denitrification,the hydroxylamine(NH2 OH)oxidation and heterotrophic denitrifiers denitrification.N2O emission data vary significantly because of the different operational conditions,bioreactor configurations,monitoring systems and quantitative methods.Under the common operational parameter scopes of PNA,N2O emission via NH2 OH oxidation dominates at relatively low dissolved oxygen(DO),low inorganic carbon(IC),high pH or low N02-concentration,while N2O emission via AOB denitrification dominates at relative higher DO,higher IC.lower pH or higher N2O-concentration.AOB are highly enriched while nitriteoxidizing bacteria(NOB)are rarely found in partial nitritation process,and the order Nitrosomonadales of AOB is the dominant group and N2O producer.Anammox bacteria,AOB and certain amount of heterotrophic denitrifying bacteria are observed in the anammox process,the genus Denitratisoma and the heterotrophic denitrifying bacteria in the deep layer of anammox granules are the dominant N2O generation bacteria.In one-stage PNA reactors,anammox bacteria account for a large fraction of the biomass,AOB account for small portion,and NOB account for even less.The microbial community,diversity and N2O producers in one-stage PNA reactors are similar with those in two-stage PNA reactors.The dominant anammox bacteria,AOB and NOB in PNA are the species Candidatus Brocadia,the genera of Nitrotoga,Nitrospira and Nitrobacter,and the genus Nitrosomonas,respectively.The relations between N2O emission pathways and microbial communities need further study in the future.     

Reversible photobluing of CdSe/ZnS/TOPO nanocrystals

Photobrightening and photobluing effects of photoluminescence (PL) from CdSe/ZnS/TOPO nanocrystal ensembles, i.e. ca. 1000 nanocrystals, have been investigated in several environments. The PL intensity increases more than twice with blue shift under continuous light irradiation in a wet nitrogen (H₂O/N₂) atmosphere, while in a pure nitrogen atmosphere and vacuum their behaviors are nothing particular. In addition, increasing rates of both the brightening and bluing effects in the H₂O/N₂ atmosphere depend on irradiation intensities. These results suggest that both effects should be associated with photo-adsorption of water molecules onto nanocrystal surfaces. As for the brightening effect, we propose that the photo-adsorption of water molecules provides some restoring functions to PL-quenching defects or trap-sites on or near nanocrystal surfaces. On the other hand, the origin of the bluing effect is not clear from the results of the ensemble measurements. To get further insight into the bluing effect, PL spectra from single nanocrystals are measured under continuous light irradiation in cyclic environments in which the H₂O/N₂ atmosphere and vacuum are alternating. As a result, blue-shifted PL induced by the light irradiation in the H₂O/N₂ atmosphere recovers almost to its initial one reversibly under evacuation. The mechanism of the photobluing effect will be discussed also on the bases of the photobrightening model introduced above.     

O2/CO2气氛下CO2和H2O气化反应对煤及煤焦燃烧特性的影响

利用热天平对比研究了大同煤及煤焦在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的燃烧行为,探讨CO₂和H₂O气化反应对其富氧燃烧特性的影响。结果表明,在5%氧气浓度下,煤粉在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的燃烧速率按顺序依次降低。氧气浓度降低到2%,由于CO₂和H₂O气化反应的作用,煤粉在高温区的整体反应速率按顺序依次增大。当氧气浓度为5%时,煤焦在O₂/CO₂中的燃烧速率要低于O₂/N₂中的燃烧速率,但燃烧反应推迟后气化反应的参与使得煤焦在O₂/H₂O/CO₂中的整体反应速率显著升高。当氧气浓度降低到2%后,随着温度的升高,在CO₂气化反应的作用下,煤焦在O₂/CO₂中的整体反应速率逐渐高于O₂/N₂中的燃烧速率。在O₂/H₂O/CO₂中,由于H₂O在共气化中起主要作用,煤焦在O₂/H₂O/CO₂高温区的整体反应速率进一步升高。动力学分析表明,在5%氧浓度时,煤焦在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的表观活化能依次升高。随着氧气浓度的降低,在不同反应气氛中的表观活化能均有所下降。     

A Novel Catalyst in N2O Decomposition-the Preparation of Cu,Co-exchanged Al-pillared Smectite and its Catalytic Activity

Nitrous oxide(N₂O) is now considered a greenhouse gas and contributes to catalytic stratospheric-ozone destruction. Therefore, the catalytic decomposition of N₂O has become one of the urgent environmental issues^[1-4].     

Electron beam treatment of lignite-burning flue gas with high concentrations of sulfur dioxide and water

Experiments were carried out to investigate the removals of SO₂ and NO_x from simulated lignite-burning flue gas containing SO₂ (4800 ppm), NO (320 ppm) and H₂O (22%) by electron beam irradiation. Removal efficiencies of SO₂ and NO_x were achieved to reach 97 and 88% at 70°C, and 74 and 85% at 80°C, respectively, with the dose of 10.3 kGy without NH₃ leakage. The higher removal efficiencies of SO₂ and NO_x were observed in simulated lignite-burning flue gas than in coal-fired flue gas containing 800 ppm of SO₂, 225 ppm of NO and 7.5% H₂O at the same treatment condition. The higher removal efficiencies were attributed to the higher concentrations of SO₂, H₂O, and added NH₃. Simulation calculations indicated that the higher concentrations of these components enhance the effective radical reactions to oxidize NO to form NO₂ with HO₂ radical, and to oxidize SO₂ to form SO₃ with OH radical and O₂. The reactions of NO_x with N and NH₂ radicals to produce N₂ and N₂O also promote the NO_x removal. By-product was determined to be the mixture of (NH₄)₂SO₄ and NH₄NO₃ containing a small amount of H₂SO₄.     

水对采空区遗煤吸附电厂烟气影响的理论计算

为研究电厂烟气注入采空区时,煤中含水率和烟气中水分对于封存温室气体CO_2和抑制煤自燃的影响,建立干煤和湿煤结构模型,采用巨正则系综蒙特卡洛方法,计算了不同水分含量的烟气组分CO_2/O_2/N2/H_2O在干煤以及不同含水率的湿煤中的吸附行为。结果表明,烟气中CO_2竞争性最强吸附量最大,O_2的物理吸附量极小,烟气中H_2O含量不影响CO_2、N2和O_2的吸附量,可不进行干燥处理直接将电厂烟气注入采空区。随着煤中含水率增加,水分占据孔隙空间,范德华作用减弱,H_2O-H_2O之间的氢键作用增强且提供了额外吸附位。H_2O的等量吸附热升高,吸附位移向吸附作用更强的低相互作用能区域,吸附大量水形成水团簇,与CO_2竞争吸附位,并且占据吸附空间抑制CO_2、O_2、N2的吸附,使其吸附量降低50%以上,因此,注入烟气时应充分考虑采空区煤体的含水率问题。     

NOFBX新型绿色推进剂燃烧化学反应动力学模型

本文以具有绿色无毒、高性能、低成本等诸多优势的N_2O-C_2烃类燃料单元复合推进剂(即NOFBX)为对象,首先发展了包含52组分、325反应的燃烧化学反应机理模型。该机理不仅能够准确计算N_2O热解过程中重要组分的分布,而且能够在较宽的温度、压力、化学计量比范围内准确预测N_2O-C_2烃类燃料体系的着火延迟时间和层流火焰传播速度。鉴于本文提出的N_2O-C_2烃类燃料反应机理具有机理规模小、实验验证充分的特点,有望在NOFBX发动机的多维燃烧数值模拟中得到广泛应用。     

Angular distributions of N2 in the photodissociation of N2O adsorbed on a partially oxidized Si(100) surface at 95 K

The time-of-flight distributions of the N₂ photofragment produced in the UV photodissociation of N₂O adsorbed on a partially oxidized Si(100) surface at 95 K have been measured as a function of the desorption angle. Photoinduced electron transfer initiates the dissociation of N₂O to produce an adsorbed oxygen atom and energetic N₂ desorbing from the surface. Interestingly, the angular distribution of N₂ originating from chemisorbed N₂O molecules is peaked at ≈ 32° from the surface normal. The results are discussed on the basis of bonding geometry and photodissociation dynamics of N₂O.     

Reactions of acyl nitroso compounds with amines: Production of nitroxyl (HNO) with the preparation of amides

Oxidation of hydroxamic acids in the presence of amines generates nitrous oxide (N₂O) and the corresponding amide. The identification of N₂O suggests the intermediacy of nitroxyl (HNO). Retro-Diels Alder dissociation of cyclopentadiene-acyl nitroso compound cycloadducts releases N₂O with amide formation.     

Adsorption of nitrous oxide on the(6,0) magnesium oxide nanotube

Nitrous oxide adsorption on the pristine（6,0） magnesium oxide nanotube was studied by using density functional theory calculations.We present the nature of the N₂O interaction in selected sites of the nanotube.Adsorption energies corresponding to adsorption of the N₂O on the nanotube were calculated to be in the range -11.67 to -22.21 kJ mol^-1.Our results indicate that the N₂O molecule has a weak physical adsorption on the pristine models due to weak Van der Waals interaction between the nanotubes and N₂O molecule.The important results can be useful in production of the N₂O sensors.     

气体再燃低NOx燃烧中NO与NHi的反应机理研究

采用量子化学密度泛函理论(DFT)对NO与NH_i自由基的反应机理进行了研究,并结合经典过渡态理论对各反应速率常数进行了计算。结果表明,NO与NH₂自由基的反应体系可通过六个反应通道形成N₂+H₂O、N₂O+H₂和N₂H+OH。从能量变化和反应速率两方面考虑,产物N₂+H₂O最容易生成,其最佳反应通道为NO+NH₂→→N₂+H₂O;NO与NH自由基的反应体系可通过七个反应通道形成N₂+OH、N₂O+H和N₂H+O;其中,N₂+OH最容易生成,最佳反应通道为NO+NH→→N₂+OH。比较发现, NH比NH₂自由基更易与NO发生反应生成N₂。因此,在实际运行中改变操作条件,实现NH₂等向NH方向转化,有利于NO_x的还原。     

LaMnAl11O19催化剂上生物质气化气燃烧中NH3-NOx的转化特性

采用共沉淀法制备了LaMnAl₁₁O₁₉六铝酸盐催化剂,采用XRD、BET和XPS对样品结构进行了表征,并通过模拟生物质气化气的燃烧实验和NH₃单独氧化实验,分别考察了催化燃烧和均相燃烧过程中NH₃的转化特性。利用原位漫反射红外光谱（in-situ DRIFT）法在线研究了NH₃在催化剂表面的吸附和氧化信息。结果表明,焙烧后催化剂形成磁铅石（MP）结构的六铝酸盐晶体,且具有较大的比表面积,Mn以+2、+3价形式存在晶体中。均相燃烧下模拟气中的NH₃在500℃开始反应,随之就有NO生成。催化燃烧工况下NH₃氧化曲线和模拟气中NH₃的转化曲线相差不大,NH₃的起燃温度为310℃,反应后随之就有NO生成,NO在350℃~800℃保持一个较高的浓度。NO₂的生成温度较高,并仅在较窄的温度区间内出现,在整个燃烧过程中仅检测到几个10^-6的N₂O,反应过程中有40%以上的NH₃转化成NO。DRIFT结果表明,催化剂作用下NH₃的转化遵循 -NH反应机理,即催化剂表面吸附的NH₃分解产生 -NH,-NH与氧原子（O）反应生成HNO,再进一步反应生成N₂或N₂O,或是 -NH直接与氧分子（O₂）反应生成NO。     

N2O Decomposition Catalyzed by K+-doped Bi0.02Co

K⁺-doped Bi_0.02Co was investigated as catalyst for N₂O decomposition. It was found that the catalytic performance of the Bi_0.02Co catalyst, which was prepared by coprecipitation method, can be effectively modified by potassium cations via impregnation. The optimized K_0.01Bi_0.02Co catalyst exhibited much higher activity compared with Bi_0.02Co and K_0.01Co for the reaction in feed gas 0.2% N₂O/Ar, irrespective of the presence or absence of impurity gas(volume fraction) 5%O₂, 2%H₂O, 0.12%NO and 10%CO₂. Characterization of the catalysts with H₂ temperature programmed reduction(H₂-TPR) and O₂ temperature programmed desorption(O₂-TPD) indicate that the Co-O bond in Bi_0.02Co was weakened by the K⁺doping, and hence the K_0.01Bi_0.02Co catalyst has much higher turnover frequency(TOF) than Co₃O₄ spinel and Bi_0.02Co for the reaction.     

自由基诱导的水溶液中氟西汀的降解:脉冲辐解及稳态辐照研究

The reactions of the pharmaceutical fluoxetine (FLX) with different radicals were investigated by pulse radiolysis. The reaction of hydroxyl radical (·OH) with FLX formed hydroxylated adduct of the aromatic ring, while oxidation of FLX by sulfate radical anion (SO₄^·-) formed benzene radical cation that further reacted with H₂O to yield the ·OH adduct. The determined rate constants of ·OH, hydrated electrons (e_aq^-), and SO₄^·- with FLX were 7.8×10⁹, 2.3×10⁹, and 1.1×10⁹ mol·L^-1·s^-1, respectively. In the steady-state radiolysis study, the degradation of FLX in different radiolytic conditions by electron beam irradiation was detected by HPLC and UV-Vis spectra techniques. It was found that FLX concentration decreased by more than 90% in both N₂O and air-saturated solutions after 1.5 kGy irradiation. In contrast, only 43% of FLX was decomposed in N₂-saturated solution containing 0.1 mol·L^-1 tert-butanol. The degradation rates of FLX in acidic and neutral solutions were higher than those in alkaline solutions. Our results showed that the degradation of FLX is optimal in air-saturated neutral solution, and ·OH-induced degradation is more efficient than SO₄^·- oxidation of FLX. The obtained kinetic data and optimal conditions give some hints to understand the degradation of FLX.     

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。     

Sensing behavior of BN nanosheet toward nitrous oxide: A DFT study

In order to develop a sensor for the detection of toxic N₂O molecules, the interaction of pristine and Aldoped BN nanosheets with an N₂O molecule was investigated using density functional theory calculations. It was found that unlike the pristine sheet, the Al-doped sheet can effectively interact with the N₂O molecule so that its electronic properties and conductivity are dramatically changed. Webelieve that replacing a B atom of the BN sheet with an Al atom may be a good strategy for improving the sensitivity of these nanosheets toward N₂O, which cannot be trapped and detected by the pristine sheet.     

纳米团簇Au19Pd和Au19Pt催化解离N2O

采用密度泛函理论研究Au-Pd和Au-Pt 纳米团簇催化解离N₂O. 首先根据计算得到Au₁₉Pd和Au₁₉Pt 团簇的最优构型(杂原子均位于团簇的表面). 以Au₁₉Pd催化解离N₂O为例研究催化解离的反应机理. 对此主要考虑两个反应机理, 分别是Eley-Rideal (ER)和Langmuir-Hinshelwood (LH). 第一个机理中N₂O解离的能垒是1.118 eV, 并且放热0.371 eV. N₂分子脱附后, 表面剩余的氧原子沿着ER路径消除需要克服的能垒是1.920eV, 这比反应沿着LH路径的能垒高0.251 eV. 此外根据LH机理, 氧原子在表面的吸附能是-3.203 eV, 而氧原子在表面转移所需的能垒是0.113 eV, 这表明氧原子十分容易在团簇表面转移, 从而促进氧气分子的生成. 因此, LH为最优反应路径. 为了比较Au₁₉Pd和Au₁₉Pt 对N₂O解离的活性, 根据最优的反应路径来研究Au₁₉Pt 催化解离N₂O, 得到作为铂族元素的铂和钯对N₂O的解离有催化活性, 尤其是钯. 同时, 将团簇与文献中的Au-Pd合金相比较, 得到这两种团簇对N₂O 解离有较高的活性, 尤其是Au₁₉Pd团簇. 再者, O₂的脱附不再是影响反应的主要原因, 这可以进一步提高团簇解离N₂O的活性.