Synthesis of ammonia in high-frequency discharges. II. Synthesis of ammonia in a microwave discharge under various conditions

The synthesis of ammonia from nitrogen-hydrogen plasma prepared using microwave discharge was studied by changing some experimental conditions, such as pressure (260–2600 Pa), power input (30–280 W), and nitrogen-hydrogen mixing ratio [H₂/(N₂+H₂)=0–1.0]. The ammonia yield increased with decreasing pressure and saturated at lower pressures. When the power input and the nitrogen-hydrogen mixing ratio were changed, the maximum yield of ammonia was obtained at the optimum experimental conditions (power input 150W; H₂/(N₂+H₂)0.75). Amounts of NH, H, and H₂ in the plasma also changed by changing the experimental conditions. From the changes in ammonia yield and amounts of NH, H, and H₂ by changing the experimental conditions, it is suggested that ammonia molecules are formed by the reaction of NH radicals not only with hydrogen atoms but also with hydrogen molecules. Otherwise, the formation and the decomposition of ammonia would occur simultaneously.     

Synergistic effects of catalysts and plasmas on the synthesis of ammonia and hydrazine

The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NH_x formed in the plasma on the catalyst surface followed by the formation of NH₃ and N₂H₄ are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.     

介质阻挡放电甲醇脱氢偶联一步合成乙二醇反应中氢气的催化作用

利用原位发射光谱表征和在线色谱分析,研究了甲醇介质阻挡放电脱氢偶联一步合成乙二醇反应中氢气的催化作用,考察了放电频率、甲醇和氢气进料量以及反应压力的影响.结果表明,在介质阻挡放电产生的非平衡等离子体中,H2不但能显著提高甲醇转化率,而且能显著提高乙二醇的选择性.在300°C,0.1 MPa,反应器注入功率为11 W,放电频率为12.0 k Hz,甲醇气体进料量为11.1 m L/min,氢气进料量为80–180 m L/min的条件下,甲醇转化率接近30%,乙二醇选择性大于75%.乙二醇收率与激发态氢原子的Hα谱线强度之间存在同增同减关系.由此推测,氢原子是起催化作用的活性氢物种.活性氢物种的生成途径是:基态氢分子通过与电子碰撞变成激发态,激发态氢分子通过第一激发态氢自动解离为基态氢原子.放电反应条件通过影响氢分子解离来影响氢气的催化作用.氢气在非平衡等离子体中显示的催化作用有可能为开辟新的化学合成途径提供重要机遇.     

Catalytic asymmetric reactions in alkaloid and terpenoid syntheses

Catalytic asymmetric induction is one of the most important methods in current synthetic organic chemistry for designing efficient and attractive synthetic routes. The efficient total synthesis of a natural product can be achieved through the identification of appropriate method and strategy. This Letter introduces the catalytic asymmetric syntheses of alkaloids and terpenoids based on an overview of four recently reported types of asymmetric reaction: (1) asymmetric decarboxylative allylation, (2) organocatalytic cascade reaction, (3) polyene cyclization, and (4) asymmetric [2+2]-photocycloaddition catalyzed by a chiral Lewis acid.     

氧化铈负载钌催化剂中钌表面密度对氨合成活性和氢中毒的影响

氨是关系国计民生的大宗化学品,也是氢能源的重要载体.目前,世界合成氨工业每年消耗约2％的世界总能源,并排放超过1％的CO2,节能降耗需求十分迫切,其中的关键在于高性能氨合成催化剂的开发.传统观点认为,B5活性位是钌催化剂上氮解离和氨合成的活性位,当钌粒子尺寸在1.8～2.5 nm时催化剂的B5活性位数量最多,而钌尺寸较小(0.7～0.8 nm)的催化剂几乎没有氨合成活性.本文通过改变钌负载量调变了氧化铈负载钌催化剂的钌表面浓度,证实钌粒子尺寸低于2.0nm时,氧化铈负载钌催化剂也具有较高的氨合成活性.XPS等表征结果证实:钌表面密度低于0.68 Ru nm-2时,钌主要以层状形式存在于氧化铈表面,层状钌与氧化铈紧密接触,电子从氧化铈的缺陷位传递给钌物种,在这种情况下,Ru 3d5/2的结合能有所下降,氮解离能力增强,这有利于提高催化剂的氨合成活性;当钌表面密度约为0.68 Ru nm-2时,钌金属传递电子给氧化铈,此时Ru 3d5/2结合能有所增加;当钌表面密度高于1.4 Ru nm-2后,钌物种优先在层状钌表面聚集成大尺寸钌纳米粒子,此时催化剂中同时存在钌团簇和钌纳米粒子,氧化铈载体对钌粒子电子性质的影响减弱,因此大尺寸钌金属颗粒Ru 3d5/2结合能又有所下降.另一方面,氢分子会在氧化铈表面形成均裂产物(两个OH基团)或异裂产物(Ce-H和OH).同时氢分子还会在0价钌金属表面解离形成氢原子,并进一步溢流到氧化铈表面与氧原子作用形成羟基.钌活性位上的氢物种比氧化铈中的氢更容易脱附,因此氧化铈中钌的存在不仅可以增强其氢吸附量,还降低了氢物种的吸附强度.当钌表面密度低时,氧化铈与钌的相互作用较强,催化剂中的氢物种容易溢流到氧化铈中形成羟基基团,此时催化剂的氢吸附能力增强,氢中毒问题较显著.当钌表面密度较高时,氢原子在大尺寸钌颗粒上移动、反应和脱附,因此催化剂的氢中毒问题也得到显著缓解.总之,对于氧化铈负载钌催化剂,氧化铈与钌金属之间的电子相互作用以及其吸附性质都会影响催化剂的氨合成活性,因此钌表面密度低于0.31 Ru nm-2以及约为2.1 Ru nm-2时,催化剂都展现出了较高的氨合成活性.本文将为设计制备高性能钌基氨合成催化剂提供理论指导.     

Doppler-broadened line shapes of atomic hydrogen in a parallel-plate radio frequency discharge

Doppler-shifted atomic hydrogen emission (Balmer ) is observed from a low-frequency rf discharge through molecular hydrogen by collecting the light through a hole in one of the electrodes. Doppler shifts as large as 0.7 nm, corresponding to an energy of 540 eV or 85% of the peak applied voltage, are observed when ions are accelerated by the sheath electric field. The mechanisms for hot atom production are discussed in terms of both gas-phase and surface ion-impact phenomena. Hot atoms are produced via gas-phase ion-atom and ion-molecule collisions, as a result of simultaneous neutralization and reflection of ions at the electrode surface, and/or by sputtering of adsorbed hydrogen. As much as 30% of the atomic hydrogen emission is substantially Doppler shifted, indicating that most of the atomic emission in the sheaths is actually produced by ion impact and not by electron impact.     

Studies on product distribution of alkali promoted iron catalyst in Fischer-Tropsch synthesis

The dependencies of hydrocarbon product distributions of alkali promoted iron catalyst in Fischer-Tropsch synthesis have been studied. The concept of two superimposed Anderson-Schulz-Flory distributions has been applied for the representation of the effects of Mg, La and Ca promoters on product distributions. The FTS performance of the catalysts was tested in a fixed bed reactor under the conditions 563 K, 1.7 MPa, H2/CO = 1 and space velocities 4.86 and 13.28 nl h-1 gFe-1 . The results indicate that approp...     

不同MgO担体对Ba-Ru/MgO氨合成催化剂物化性质和反应性能的影响

采用不同沉淀剂制备了MgO材料,以其为载体制备了Ba-Ru/MgO氨合成催化剂,考察了沉淀剂种类和BaO助剂对其氨合成性能的影响.通过X射线衍射(XRD)、N2物理吸附、X射线荧光光谱(XRF)、透射电镜(TEM)、H2程序升温还原(H2-TPR)、CO2程序升温脱附(CO2-TPD)、H2程序升温脱附(H2-TPD)和N2程序升温脱附(N2-TPD)表征手段,对不同沉淀剂影响Ba-Ru/MgO催化剂氨合成性能的原因进行了探索.结果表明:采用(NH4)2CO3作沉淀剂制备的Ba-Ru/MgO催化剂表面Ru物种易于在低温下还原,催化剂表面在低温区具有较多数量的弱碱性吸附位,在450℃、5.0 MPa和5 000 h-1条件下,由(NH4)2CO3做沉淀剂制备的Ba-Ru/MgO催化剂活性最高,出口氨浓度为3.74%.BaO助剂的加入大大减少了Ba-Ru/MgO催化剂表面吸附氢的数量,增大表面脱附氮的数量,从而易于N2解离吸附,提高氨合成反应速率.     

Reaction of hydrogen with aromatic compounds in a 13.6-MHz discharge

A series of aromatic compounds C₆H₅X (X=CH₃, Cl, NO₂, NH₂, OCH₃, CO₂CH₂CH₃, COCH₃, CN) were reacted with hydrogen in a 13.6-MHz inductively coupled glow discharge. The flow rates of aromatic and hydrogen were typically 0.5 mmol/min and 18 mmol/min, respectively. The applied power was varied from 50–200 W and the total pressure was varied from 2–14 torr. The products were collected and analyzed by gas chromatography. Three types of reactions were observed: (1) addition of hydrogen to the aromatic, (2) replacement of the group X by hydrogen, and (3) reactions characteristic of aromatic in the absence of hydrogen. The toluene reaction was studied most carefully. Methylcyclohexenes and benzene were the major products identified. The benzene was optimized by increasing the power and decreasing the pressure of either hydrogen or toluene. Reaction of toluene-d₈ with hydrogen revealed that hydrogens were sequentially exchanged for deuteria on toluene and each of the products. A new apparatus is described which allows flow rates and pressure to be preselected and controlled and which allows a series of product samples to be collected without quenching the plasma.     

离子色谱法测定空气中的氨、肼和乙醇胺

建立了抑制型离子色谱同时检测空气中氨、肼和乙醇胺的分析方法,并应用于评价工作场所空气的安全性。空气中的氨、肼和乙醇胺经甲基磺酸（MSA）水溶液吸收后,用0.22 μm滤膜过滤,除去不溶颗粒。使用新型ThermoFisher IonPac CS19羧酸型阳离子交换分析柱（250 mm×4 mm）和CG19保护柱（50 mm×4 mm）,以淋洗液发生器产生的MSA作为流动相,等度洗脱,采用抑制型电导检测器,同时分离和检测铵、肼和乙醇胺。结果表明,铵、肼和乙醇胺的检出限分别为0.003、0.011和0.016 mg/L,RSD为0.98%~1.6%。本方法操作简便,样品无需衍生化等复杂的前处理过程,在15 min内可完成对铵、肼和乙醇胺3种组分的分离测定,有效缩短检测时间,提高工作效率,具有较高的实用价值。     

K促进的Fe/椰壳炭催化剂对甲烷氮气常压合成氨性能的影响

采用等体积浸渍法制备了一系列催化剂用于甲烷氮气常压合成氨反应.对Si O2、γ-Al2O3、煤质柱状炭、椰壳活性炭为载体的Fe基催化剂的活性评价结果显示椰壳炭载体最优;通过对Zr、Ce、K等多种助剂的筛选,发现K促进的Fe基催化剂氨生成速率最高.利用XRD、SEM、BET等手段对载体和催化剂进行表征,结果表明椰壳炭具有规则孔道且孔容增大,催化剂还原后有新晶相KFe O2生成.最后在固定床微分反应器中,考察了常压合成氨催化剂的负载顺序及最优工况.结果表明,在常压700℃、VCH4/VN2=2/1、空速为2 800 m L/h时,催化剂3%K-5%Fe/椰壳炭的氨生成速率最高可达1.04×10-6mol·g-1·s-1,是现有文献值的83.5倍,将具有深远的工业应用前景.     

不对称催化反应在手性农药不对称合成中的一些应用

近十多年来，不对称催化反应在单一手性农药研发中的应用渐渐引起人们的关 注，结合自己的研究对这一领域的不对称催化反应及手性催化剂的发展进行了归纳 总结。     

Radial distribution measurement of SiH* in a low-pressure silane plasma

The radial emission intensity distribution of SiH^* (A²,v=0) over the substrate of a low-pressure silane plasma was investigated for various substrate temperatures (T _s=20–320°C). Measured lateral intensities were converted to radial emission coefficients using an Abel inversion. The intensity near the center of the substrate was found to increase withT _s and yielded an activation energyE _a of 1.1 kcal/mole. This result is consistent with the value ofE _a determined by laser-induced flourescence measurements obtained previously. Radially resolved emission data obtained by varying the operating parameters of rf power, gas flow rate, silane/argon mixing rate, and total gas pressure provide a useful means of determining the conditions necessary to generate a uniform plasma.     

In situ FTIR diagnostics of the radio-frequency plasma decomposition of N2O

The decomposition of N₂O in a 13.56-MHz parallel-plate system was studied usingin situ Fourier transform infrared (FTIR) spectroscopy. Areas of two infrared absorption bands of N₂O recorded at 8 cm^–1 resolution were used to estimate relative gas-phase dissociation as a function of rf power and flow rate at 500 mT. Flow rate was found to strongly affect band areas over the range of powers investigated (10–90 W). The effect of rf power on band areas diminished above 40 W, probably due to poor plasma confinement. Distortion of the band shapes by the plasma permitted rotational temperatures to be estimated. Rotational temperature increased essentially linearly with power at constant flow rate, reaching 450 K at 80 W, but was independent of flow rate at constant power. Rotational temperatures were also found to depend on the temperature of the electrodes, which were heated by plasma exposure. No infrared-active product species were observed even under batch conditions where all N₂O was irreversibly dissociated. This lack of detectable products and a 50% pressure rise observed in a batch study suggest that N₂ and O₂ are the primary stable discharge products.     

射频等离子体对合成低碳醇用CuCoAl催化剂的改性作用

采用共浸渍法制备了CuCo/γ-Al₂O₃催化剂,应用射频等离子体技术对催化剂进行改性处理。以CO加氢合成低碳醇为模型反应对催化剂进行活性评价,通过X射线物相分析(XRD)、氢氧滴定(HOT)、CO程序升温脱附(CO-TPD)和程序升温还原(TPR)等技术对催化剂进行表征,研究了射频等离子体技术强化处理对催化剂结构、吸附性能和还原性能的影响。结果表明,等离子体技术改性处理提高了催化剂活性组分的分散度,细化了铜物种的晶粒尺寸,增加反应活性位并调变了活性位对吸附物种的吸附强度,改进了催化剂的还原性能,等离子体改性处理的催化剂比未处理的样品CO加氢反应活性和低碳醇的时空产率显著提高。     

Kinetics and mechanism in the decomposition of NH3 in a radio-frequency pulse discharge

Studies of time-resolved absorption spectra of transient species in the decomposition of NH₃ by an r.f. pulse discharge together with product analysis showed that the major radical formed was NH at concentrations of the order of 10^–6 mol dm^–3 (10⁵ molec. cm^–3). Possible mechanisms for the formation of the radical during the discharge and its decay following pulse cut-off were tested by computer simulation of the kinetic data. Following zero-order formation with rate coefficient 0.19±0.03 mol dm^–3 s^–1, the decay was second order in NH with rate coefficient 2.1±0.5×10⁹ mol^–1 dm³ s^–1 both for pure NH₃ and where NH₃/rare gas mixtures were investigated. The kinetic data are consistent with NH removal in a nonassociative radical-radical reaction proceeding via a short-lived collision complex, probably 2NH N₂H₂ N₂ + H₂.     

Kinetics and mechanism in the decomposition of CCl4 in a radio-frequency pulse discharge

In the decomposition of CCl₄ in an r.f. pulse discharge the observation of time-resolved absorption spectra of the CCl radical allowed concentration measurements and a kinetic and mechanistic investigation of the system. Kinetic spectroscopy and end product analysis, with computer simulation of proposed mechanisms, indicates that the major decomposition reaction is CCl₄»CCl+3Cl (Cl₂+Cl), with a minor contribution from CCl₄»CCl₂+2Cl. Radical concentrations were of the order of 10^–7 mol dm^–3 (10¹⁴ molec. cm^–3). CCl removal was kinetically second order with a rate coefficient value of (3.7±8)×10¹⁰ mol^–1 dm^–3 s^–1 at 295±3 K at gas pressure 0.1 torr.     

Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

介孔炭的孔结构对其负载的Ru基氨合成催化剂性能的影响

采用模板法合成了介孔炭(MC),研究了其孔结构对其负载的Ru基氨合成催化剂Ba-Ru-K/MC性能的影响,采用N₂吸附脱附、扫描电镜和透射电镜等手段对介孔炭的孔结构进行了表征.研究发现,介孔炭载体的孔结构取决于模板剂的用量,当SiO₂/C质量比为1.0时,所制介孔炭比表面积最大.介孔炭负载的Ba-Ru-K催化剂活性与其介孔比表面积相关.在425℃,10MPa和10000h^-1条件下,合成氨的反应速率为139mmol/(g_cat·h).     

A highly stable and active mesoporous ruthenium catalyst for ammonia synthesis prepared by a RuCl3/SiO2-templated approach

Molecular nitrogen is relatively inert and the activation of its triple bond is full of challenges and of significance. Hence, searching for an efficiently heterogeneous catalyst with high stability and dispersion is one of the important targets of chemical technology. Here, we report a Ba-K/Ru-MC catalyst with Ru particle size of 1.5–2.5 nm semi-embedded in a mesoporous C matrix and with dual promoters of Ba and K that exhibits a higher activity than the supported Ba-Ru-K/MC catalyst, although both have similar metal particle sizes for ammonia synthesis. Further, the Ba-K/Ru-MC catalyst is more active than commercial fused Fe catalysts and supported Ru catalysts. Characterization techniques such as high-resolution transmission electron microscopy, N₂ physisorption, CO chemisorption, and temperature-programmed reduction suggest that the Ru nanoparticles have strong interactions with the C matrix in Ba-K/Ru-MC, which may facilitate electron transport better than supported nanoparticles.