催化还原脱硝的密度泛函理论研究进展

随着工业化进程的加快,NOx的排放量不断增加,对环境和人体健康造成了严重影响。脱除NOx的方法较多,目前工业上常用的催化还原脱硝（SCR）的脱除方法。随着理论化学的不断完善及计算水平的不断提高,利用密度泛函理论研究催化脱硝过程已经成为认识SCR催化过程机理的重要手段。本文综述了运用密度泛函理论进行SCR研究的进展。     

TADFIW水解反应机理的密度泛函理论

应用密度泛函理论(DFT)在B3LYP/6-31G(d,p)水平下对四乙酰基二甲酰基六氮杂异伍兹烷(TADFIW)甲酰基的水解反应机理进行了研究.结果表明,TADFIW上的甲酰基水解时,甲酰基被质子化,碳氧双键中的氧原子带有负电荷0.619 e,碳原子带有正电荷0.471 e,亲核试剂水分子进攻质子化甲酰基的碳原子,同...     

单空缺石墨烯负载的Pd单原子催化剂上NO还原的密度泛函理论研究

采用密度泛函理论（DFT）方法对单空缺石墨烯负载的Pd单原子（Pd/SVG）催化剂上H₂还原NO的反应进行了研究,探究了Pd/SVG上NO还原生成N₂和NH₃的路径。在Pd/SVG上NO容易加氢形成HNO,需要的活化能为67.0 kJ·mol^-1,显示了极高的催化活性。N₂生成的有利路径为NO活化生成HNO后,HNO继续加氢生成中间体NH₂O和NH₂OH,然后NH₂OH解离生成NH₂和OH,生成的NH₂中间体结合NO形成NH₂NO,然后NH₂NO异构化形成的NHNOH再经解离生成N₂与H₂O,这个过程中的决速步骤为NH₂NO分子内氢转移生成NHNOH,能垒为144.3 kJ·mol^-1。对于NH₃的生成,从NO的活化到中间体NH₂的形成与N₂的形成过程相同,最后NH₂加氢即可形成NH₃,这个过程中的决速步骤为NH₂O加氢生成NH₂OH,能垒为86.4 kJ·mol^-1。比较生成N₂和NH₃的决速步能垒可见,Pd/SVG催化剂上NO经H₂还原更容易形成NH₃。本研究为石墨烯负载型Pd基催化剂上H₂还原NO的实验及工业应用提供理论参考。     

FMNH介导偶氮苯还原机理的密度泛函理论研究

实体瘤的低氧微环境是恶性肿瘤的重要特征之一,针对肿瘤低氧的靶向化疗药物为癌症治疗带来了新策略。偶氮苯中的偶氮基团具有低氧激活的特异性,能够在常氧条件下稳定存在而在低氧条件下发生还原裂解,因此一些偶氮苯衍生物前药也因其具有肿瘤低氧靶向潜力,近年来被开发并应用于临床研究。使用密度泛函理论(DFT)对在辅酶还原型黄素单核苷酸(FMNH)作用下的偶氮苯还原机理进行了研究。结果表明,优势反应路径为偶氮苯首先经过连续的两步1e^-/1H⁺转移形成1,2-二苯肼,然后依次再发生第3次1e^-/1H⁺转移、氮氮裂解和第4次1e^-/1H⁺转移后最终形成两分子苯胺。其中,前两步1e^-/1H⁺转移需要克服最高能垒,为反应的控速步骤。这些结果为设计开发新型的肿瘤靶向性低氧激活前药提供了重要理论依据。     

四种白藜芦醇含氮衍生物的密度泛函理论计算

采用密度泛函理论(DFT) B3LYP-D3方法,对四种白藜芦醇含氮衍生物的分子结构、红外光谱、电子吸收光谱及抗氧化活性进行计算研究。计算结果表明,甲氨基更有利于增强衍生物分子结构中A,B苯环共平面性,扩大了分子的π共轭体系。四种化合物电子吸收光谱最大吸收峰具有电子的π-π*跃迁特征,在溶剂的作用下,λ_(max)红移了15～17 nm,但随着溶剂极性的增大,λ_(max)变化不明显。四种含氮衍生物电离能(IP)和能隙(E_(gap))均低于白藜芦醇,具有更好的抗氧化活性。     

沙林的密度泛函理论研究

本文应用密度泛函理论的B3LYP方法,在6-31G(d)基组水平上对沙林分子进行了研究,计算得到了沙林分子的稳定构型及其红外光谱。分析后发现,根据分子振动类型的不同,可将红外光谱划分为(0~1300)、(1300~1450)、(1450~3000)和(3000~4000)cm-1 4个区域,且红外光谱中实际振动峰的数目小于简正振动的数目。     

密度泛函理论中的界限研究

自从密度泛函理论建立以来 ,已被广泛成功地用来处理原子、分子和晶体的结构 ,然而严格的能量泛函至今还没有建立 ,因此密度泛函理论中的界限研究就成为一种重要的研究方法 ,通过对界限的研究 ,为寻找近似泛函和严格的泛函指明方向。本文简要介绍密度泛函理论的基础和近几年作者在密度泛函理论中的界限研究所取得的进展。     

硫酸乙烯酯及其改性分子氧化还原稳定性的密度泛函理论研究

基于密度泛函,分别从HOMO/LUMO和氧化/还原电位两个角度研究硫酸乙烯酯分子(DTD)及其改性分子的氧化/还原稳定性。通过垂直电离势的方法对化合物电位进行计算,模拟数值与实验数值有较好的吻合,电位展现出的氧化/还原稳定性趋势与分子的HOMO/LUMO相符。针对DTD分子结构改性,CO或CC基团的引入对添加剂的氧化稳定性和还原稳定性无益,改性分子的电化学稳定窗口反而变窄。     

香兰素的密度泛函理论研究

本文应用密度泛函理论(DFT)的B3LYP方法,在6-31G(d)基组水平上对香兰素进行了研究,计算得到了分子的稳定构型,并对其进行了频率分析,然后利用Gaussview图形软件将频率分析数据转换为红外振动光谱,结果表明,香兰素分子构型属C1点群,分子构型呈现出良好的对称性。对红外振动光谱分析后发现,按照分子振动模式的不同可将光谱划分为4个区域,即0~400、400~1333、1333~1640和1640~4000cm-1。此外,文中对各条谱峰的认定和归属等问题进行了详细讨论,发现红外光谱中振动峰的实际数目远小于简正振动的数目。     

对乙酰氨基酚的密度泛函理论研究

本文应用密度泛函理论的B3LYP方法,在6-31G(d)基组水平上对对乙酰氨基酚分子进行了理论计算,得到了分子的稳定构型及其红外光谱。分析后发现,根据分子振动类型的不同可将红外光谱划分为(0～500)cm-1、(500～3000)cm-1和(3000～4000)cm-1 3个区域。此外,由于存在简并和无红外活性的现象,红外谱中实际谱线的数目小于实际简正振动的数目。该研究有助于更好的了解对乙酰氨基酚的结构特点和红外光谱特性,为对乙酰氨基酚的实际运用提供一定的理论指导。     

Experimental study of NO reduction over biomass char

Some biomass fuels produce more NO_x than coal on the basis of heating value, giving rise to the necessity and importance of controlling NO_x emission in biomass combustion. The present study investigated the NO reduction over biomass char in a fixed bed quartz reactor in the temperature range of 973–1173 K. The reaction rates of three biomass chars (sawdust, rice husk and corn straw) with NO were compared with Datong bituminous coal char. The results show that the reaction orders of biomass chars for NO are of fractional order and independent of temperature. Biomass chars are more active in reducing NO than coal char. The characteristics of biomass char affect NO conversion. Biomass char formed at high pyrolysis temperature, especially large in particle size, is less active in reducing NO. To some extent, increase of reaction temperature and char loading enhance NO conversion. There exists an optimum bed height for the highest NO conversion. Moreover, NO reduction over biomass char is also enhanced in the presence of CO, O₂ and SO₂.     

Detailed surface reaction mechanism for reduction of NO by CO

In order to meet the stringent regulatory norms of NO_x and CO emitted by automobiles, reduction of these pollutants has become an intense field of research. Various catalysts like Pt, Rh, Ir, Cu, and Fe have been found to possess high activity for the reduction of NO. However, the available detailed surface reaction mechanisms are not satisfactory in clarifying all the aspects of the simultaneous reduction of NO and oxidation of CO. Here we have developed a quantitative surface reaction mechanism based on elementary steps, in order to comprehend the phenomena of catalytic reduction of NO by CO. Eleven elementary steps are proposed for the NO–CO and NO–CO–O₂ systems on Pt group catalysts. The elementary reaction mechanism is coupled with the continuously stirred tank reactor/packed bed reactor models and the simulation results are validated against literature experiments for the NO–CO reaction on Pt, and the NO–CO–O₂ reaction on Ir catalyst. Despite the simplicity, the CSTR model is able to capture the observed phenomena well on Pt and Ir catalysts. The effect of O₂ on the activity of CO for NO reduction is also analysed in detail through the simulations.     

Effect of pyrolysis temperature on the char micro-structure and reactivity of NO reduction

A phenol-formaldehyde resin (PFR) and a bituminous coal (SH) were pyrolyzed at various temperatures. The structure and the char-NO reactivity were analyzed in order to examine the effect of pyrolysis temperature on the micro-structure of the resulting char and further on the reactivity towards NO. Micro-structure of the char samples was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy. It was indicated that the micro-structure of PFR char and coal char experienced remarkable changes during pyrolysis, which resulted in the decrease of phenolic OH, aromatic hydrogen and more ordered structure. The pyrolysis temperature showed a weak impact on the reactivity of PFR char but comparatively remarkable impact on that of coal char at lower reaction temperature. Mineral matter in coal char presented a weak effect on the reactivity. This paper was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

碳氧官能团对煤焦低温还原NO的影响

在450℃对神木煤制半焦还原NO进行研究,采用Raman、FT-IR、XPS等分析方法探究了半焦脱硝影响因素与其表面碳氧官能团的关系。结果表明：热解制焦温度、烟气中氧气浓度以及负载金属对脱硝效果的影响都与半焦表面碳氧官能团有关,降低热解温度、增大氧气浓度、负载金属均有利于增加C—O官能团。采用XPS表征对金属负载半焦表面的碳氧官能团进行分析,发现热力学相对稳定的C—O官能团含量与脱硝指标之间存在明显的线性关系(R²>0.96)。研究进一步揭示了热力学稳定的C—O官能团在半焦脱硝过程的重要地位。     

Density functional study of graphite bulk and surface properties

The structural and electronic properties of bulk graphite were compared using density functional theory calculations with the local density (LDA) and generalized gradient (GGA) approximations to determine the relative ability of each to model this material. The GGA fails to generate interplanar bonding, but the LDA does, even though the band structures obtained from both approximations were essentially identical. The atomic geometry, electronic structure, and enthalpy of the graphite (0 0 0 1) surface were then obtained using the LDA. The calculated surface energy was ∼0.075 J/m² and the calculated work function was in 4.4-5.2 eV range, both of which correspond well to published, measured and calculated values. The surface is semi-metallic, just like in the bulk, with the conduction band minimum and valence band maximum just touching with minimal overlap in the H-K region in the Brillouin Zone, so the electron affinity was identical to the work function. The (0 0 0 1) surface undergoes no noticeable relaxation and no reconstruction, as the strong covalent bonding prevents any corrugation of the basal planes.     

酚醛树脂热裂解反应机理的密度泛函理论研究

选取2,2’-亚甲基二酚作为酚醛树脂的模型化合物,采用密度泛函理论(DFT),从原子活性和化学键级的视角预测反应趋势,提出反应路径,结合动力学和热力学分析确定各路径优先顺序和产物生成机理。结果表明：由于酚羟基与亚甲基的高活性,酚醛树脂的裂解首先发生脱水缩合反应;亚甲基桥断裂是主要的初始裂解反应,主要生成苯酚及邻甲酚;高活性的酚羟基易解离成·OH,后续反应中亚甲基被·OH氧化,经脱羰基和羧基反应生成苯酚、CO和CO₂。对于硼改性酚醛树脂的裂解过程,结果显示：硼酸酯结构中的B—O键活性很低,不易断裂,热稳定性增强。亚甲基桥更稳定且脱羰基和羧基的趋势明显减弱,且动力学分析发现其能垒均有增加,表明硼的引入能有效提高其热稳定性和残炭率。     

不同热解条件下制备的污泥炭低温还原NO

以市政污泥为原料热解制备污泥炭,开展了污泥炭催化还原NO的实验研究。考察了不同热解温度（400℃、600℃和800℃）和污泥初始含水率（0、66%和80%,质量分数）条件下热解制备的污泥炭的脱硝性能。研究表明,污泥炭中包含大量铁元素（41.1mg/g）,提高热解温度可促进污泥炭中亚铁化合物（Fe₂P和FeS）的生成,使铁元素具备催化还原NO的能力,从而显著提高污泥炭的脱硝效率。提高污泥热解初始含水率可显著提高污泥炭比表面积,污泥炭对NO的低温还原能力也随初始含水率提升而显著提高。通过对污泥炭的比表面积、X射线衍射（XRD）和傅里叶红外（FTIR）分析表征,结果表明污泥炭中亚铁化合物的生成是影响NO转化的关键影响因素,而比表面积和表面官能团类型对污泥炭脱硝反应并无明显影响。     

Study on NO heterogeneous reduction with coal in an entrained flow reactor

The effects of coal types with a wide range of volatile matter content including lignite, bituminous coal, and lean coal, as well as the effects of reaction temperature, coal particle size, the primary-zone stoichiometry (SR1) and reburning-zone stoichiometry (SR2), etc. on NO reduction efficiency were carried out systematically in an entrained flow reactor. The heterogeneous NO reduction mechanism was analyzed. The results indicate that the NO reduction efficiencies increase with decreasing SR2 and coal particle size, and with increasing reaction temperature. The char contributions to the total NO reduction efficiency increase with increasing proximate volatile matter, coal particle size, and with decreasing reaction temperature. The char contribution can be reached more than 40% when SR2 is larger than 1.06 or less than 0.92 for XLT lignite. The char contribution at the conditions of SR1 = 1.0 and SR1 = 1.2 is significantly larger than that at SR1 = 1.1 for coals with high-volatile matter at a fixed reburning fraction.     

Synthetic coal chars for the elucidation of NO heterogeneous reduction mechanisms

In the present work, the mechanisms involved in NO–char heterogeneous reduction have been studied using a synthetic coal char (SC char) as carbon source. Another synthetic char (SN char) without nitrogen in its composition has also been employed in these studies. Isothermal reduction tests at different temperatures have been carried out. Two temperature regimes were considered: low temperature (T < 250 °C) where NO chemisorption takes place and high temperature (T > 250 °C) where NO–C reaction occurs. Step response experiments combining consecutive reaction stages with NO and ¹⁵NO were performed in order to determine the role of nitrogen surface complexes, C(N), in the reduction process. The results revealed N₂ and CO₂ to be the main reduction products under the experimental conditions employed in this work. NO chemisorption at lower temperatures results in N₂ emission and surface complexes (mainly oxygenated) formation, while char gasification by NO involves a direct NO attack on the char surface to form surface complexes. As a consequence of desorption of these complexes new sites of reaction are created.     

Kinetics and mechanism of NO reduction with CO on Ir surfaces

The adsorption and thermal reactivity of NO and CO and the kinetics of the NO reduction with CO on Ir surfaces were studied using X-ray photoelectron spectroscopy, polarization modulation infrared reflection–absorption spectroscopy, and temperature programmed desorption. The NO adsorption and dissociation activity was strongly dependent on the Ir surface structure. The NO dissociation activity of the Ir planes decreased in the order (100) > (211) ? (111). In contrast, the type of the CO adsorption site was independent of the Ir surface structure. The activity of Ir(111) for N₂ and CO₂ production from the NO + CO reaction was low compared with the activities of Ir(100) and Ir(211). The kinetic data for an Ir/SiO₂ powder catalyst were similar to data obtained for Ir(211). The order of the turnover frequencies for N₂ and CO₂ formation for the Ir planes was in good agreement with the order for NO dissociation activity, and this agreement indicates that the catalytic activity for NO reduction was dependent on NO dissociation. A kinetic study of the elementary steps indicated that the rate-limiting step for NO reduction with CO was the NO dissociation step.