GaN-MOVPE寄生反应的密度泛函理论研究

利用量子化学的密度泛函理论,探讨了TMG(Ga(CH₃)₃)/NH₃/H₂体系中的气体反应机理,特别关注了氨基物DMGNH₂的形成及其后的纳米粒子形核路径。通过计算不同温度下不同反应路径上Gibbs自由能的变化,从热力学和动力学两方面分析纳米粒子形核可能的产物。研究发现当T<622 K时,氨基物DMGNH₂可由加合物TMG:NH₃脱去CH₄生成,也可由TMG和NH₃双分子碰撞直接生成;当T>622 K时,氨基物DMGNH₂直接由TMG和NH₃双分子碰撞反应生成。当 662.5 K<T<939 K时,二聚物[DMGNH₂]₂相继脱去CH₄,变成[MMGNH]₂的反应容易发生。当389 K<T<734.7 K时,三聚物[DMGNH₂]₃相继脱去CH₄,变成[MMGNH]₃的反应容易发生。对于[MMGNH]₂和[MMGNH]₃相继脱去CH₄的反应,因为所有反应的ΔG>0,所以很难生成[GaN]₂和[GaN]₃。因此认为[MMGNH]₂和[MMGNH]₃是GaN-MOVPE低聚物纳米形核最可能的产物。     

硅和四氯化硅耦合加氢反应体系的热力学分析

基于Gibbs自由能最小原理,对硅和四氯化硅（SiCl₄,STC）耦合加氢反应体系进行了热力学分析。通过化学平衡产物组成分布的分析,确定了反应体系主要产物为三氯硅烷（HSiCl₃,TCS）、二氯硅烷（H₂SiCl₂,DCS）、盐酸（HCl）,并构造了3个相应的独立反应,讨论了对应的反应热（ΔrHθm）、自由能（ΔrGθm）和平衡常数（Kθp）与温度的关系。计算所采用的温度为673~923 K,压力为101.325 ~2 026.5 kPa,原料H₂与SiCl₄物质的量比为1~5。结果表明,生成TCS和DCS的反应为体系随着温度升高,四氯化硅平衡转化率及三氯硅烷产率降低;高压和适中的原料配比（H₂与SiCl₄物质的量比）有利于四氯化硅转化率及三氯硅烷产率的提高。     

二甲基一氯硅烷和三氯氢硅的热氯化反应及机理研究

去除三氯氢硅(SiHCl₃)中的碳杂质可提高多晶硅的纯度，但SiHCl₃和二甲基一氯硅烷[(CH₃)₂SiHCl]的沸点极为接近，在精馏过程中易形成共沸物。因此，SiHCl₃中的(CH₃)₂SiHCl较难去除。提出以Cl₂为氯源，通过热氯化反应将(CH₃)₂SiHCl转化为高沸点的甲基氯硅烷，以增大相对挥发度，便于后续精馏除杂。但(CH₃)₂SiHCl和SiHCl₃会同时发生氯化反应，为此，探究了两者转化率随温度的变化。结果表明，在60℃、120 min时，(CH₃)₂SiHCl的转化率为53.1%,SiHCl₃的转化率为14.3%,(CH₃)₂SiHCl的转化率最佳。最后，通过密度泛函理论计算分...     

Zn(Ⅱ)配合物催化C—C键裂解和原位合成2-甲基-4(3H)-喹唑酮

在配合物的水热合成过程中往往可以发现新的化学反应和催化机理。本文通过[Zn(L)₂·(H₂O)₂·(NO₃)₂]（L=4(3H)-喹唑酮）配合物在130℃催化乙腈分子中的CC键断裂，原位合成化合物2-甲基-4(3H)-喹唑酮。利用红外、元素分析和X射线单晶衍射表征分析2-甲基-4(3H)-喹唑酮和[Zn(L)₂·(H₂O)₂·(NO₃)₂]的结构，结果表明[Zn(L)₂·(H₂O)₂·(NO₃)₂]和2-甲基-4(3H)-喹唑酮属于三斜晶系，P-1空间群。三组温度控制实验表明，温度对2-甲基-4(3H)-喹唑啉酮的形成有着重要的影响，并且温度高于130℃有利于该催化反应的进行。采取电喷雾质谱表征2-甲基-4(3H)-喹唑酮的形成机理发现，[Zn(L)₂·(H₂O)₂·(NO₃)₂]催化乙腈分子中的CC键断裂，生成(CN)₂和·CH₃。·CH₃有选择性地引入到4(3H)-喹唑酮中的C原子和N原子之间。本文对原位引入CH₃有着指导作用。     

3种PLA/OMLS纳米复合材料的结构、结晶行为与力学性能的对比研究

采用同向旋转啮合双螺杆制备了3种不同有机改性剂改性的纳米蒙脱土(OMLS)与聚乳酸(PLA)纳米复合材料。采用X射线衍射仪和透射电子显微镜、差示扫描量热仪等研究了复合材料的结构和结晶行为。结果表明,3种PLA/OMLS纳米复合材料(OMLS质量分数为2%)均具有剥离结构,且OMLS的有机改性剂分子链越长,插层的OMLS间距越大;3种OMLS都大大加速了PLA的结晶,减小了PLA晶体尺寸;3种OMLS中,CH₃(CH₂)₁₇N(CH₃)[(CH₂CH₂OH)₂]~+改性的OMLS对PLA的结晶行为影响最大,其纳米复合材料的冲击强度最高;而CH₃(CH₂)₁₇NH₃~+和HOOC(CH₂)₁₇NH₃~+改性的OMLS对PLA的增强效果明显。     

Study on the epoxidation of olefins with H2O2 catalyzed by biquaternary ammonium phosphotungstic acid

Selective epoxidation of olefins is an important field in chemical industry. In this work, we developed a new phosphotungstic acid catalyst {[(C₈H₁₇)(CH₃)₂N]₂(CH₂)₃}_1.5{PO₄[WO(O₂)₂]₄} with long carbon chain and biquaternary ammonium cation. Cyclohexene could be epoxidized to cyclohexene oxide in 96.3% conversion and 98.2% selectivity. The catalyst type, solvent type...     

基于SiC CVD工艺的MTS-H2前驱体热解动力学研究

为了研究三氯甲基硅烷-氢气(MTS-H₂)前驱体在碳化硅(SiC)化学气相沉积工艺(CVD)过程中的热解动力学，利用DETCHEM软件，在不同沉积温度、α值和系统压力下对其在零维和一维反应器中的的气相组分进行了数值模拟。结果表明：在零维反应器中，各温度下的主要气相组分为HCl、CH₄、C₂H₆、SiCl₄、CH₄SiCl₂、SiHCl₃、SiH₂Cl₂和SiH₃Cl，温度越高气相组分可达到气相平衡的时间越短。900℃气相组分浓度达到平衡的时间约为5 s,1000℃下的气相组分浓度达到平衡的时间约为2 s,1100℃下的气相组分浓度达到平衡的时间小于1 s。随着温度增加，气相反应加剧，生成了更多的Si-Cl气相组分。气相组分浓度受α值变化的影响较小，达到气相平衡的时间基本一致。体系压力对气相组分有显著影响，增大压力有助于提高各组分的平衡浓度，但达到气...     

低密度陶粒支撑剂的水敏老化机理研究

低密度陶粒支撑剂良好的性能在非常规能源开采工作中显得十分重要。针对低密度陶粒支撑剂在地层水服役期间性能退化的现象，本文选取两种不同规格的支撑剂，在地层水中浸泡不同时间后取出，采用XRF、XPS、XRD、SEM、TEM对浸泡前后的支撑剂进行表征，探索支撑剂老化机理。结果显示：支撑剂中ClO₂含量增加，Al₂O₃、SiO₂含量减少，地层水中Cl^-、HCO^-₃含量减少；XPS检测出Cl 2p峰和Cl 2s峰；XRD检测出新相SiCl₄。以上结果证实，地层水中的Cl^-扩散到支撑剂表面与SiO₂反应生成SiCl₄,SiCl₄进一步水化生成硅凝胶或硅酸凝胶包覆在支撑剂表面。支撑剂中Al₂O₃会与地层水中H⁺(酸性环境)反应生成Al³⁺,Al^3...     

一维直孔道MOFs对CH4/N2和CO2/CH4的分离

非常规天然气未来可以作为常规天然气的有效补充,其中低浓度煤层气和生物质燃气分别需要脱除大量的N₂ 和CO₂以达到富集和纯化CH₄的目的。本研究针对CH₄/N₂这一对较难分离的气体组合,选取了具有一维菱形孔道的MOFs材料Cu(INA)₂作为吸附剂,将合成的样品做了XRD和TG表征,测试了纯气体CO₂、CH₄和N₂的吸附曲线,利用巨正则系综蒙特卡罗(GCMC)分子模拟和理想吸附溶液理论(IAST)计算了气体的吸附热和该材料对于CH₄/N₂和CO₂/CH₄的吸附选择性系数;3 MPa压力下制备的颗粒样品填装吸附分离装置,进行了混合气体CH₄/N₂ (50%/50%)和CO₂/CH₄ (50%/50%)的穿透试验,分离的结果显示,Cu(INA)₂不仅高选择性地吸附CH₄/N₂混合物中的CH₄(S_CH4/N2=10),而且对CH₄/N₂的分离效果优于CO₂/CH₄。     

(NH4)2S吸收净化冶炼烟气中SO2回收硫资源的方法

采用(NH₄)₂S溶液吸收净化高浓度SO₂烟气,得到(NH₄)₂S₂O₃和NH₄HSO₃的混合溶液并转移至高压反应釜中,控制反应条件,两种物质发生自氧化还原反应,生成硫磺和(NH₄)₂SO₄.实验考察了吸收SO₂过程和自氧化还原过程的影响条件,结果表明:在pH=3～7,SO₂气体流速300 ml·min^-1,(NH₄)₂S浓度为0.2～1.2 mol·L^-1,常温条件下,烟气中二氧化硫的吸收率达到99.8%以上,且无H₂S生成;在pH=2.5～3.0,温度为130℃条件下,反应进行1 h,硫磺收率达到95%以上,溶液经过蒸发结晶得到(NH₄)₂SO₄.用X射线衍射(XRD)和X射线荧光光谱(XRF)对硫磺和硫酸铵进行表征分析,结果表明:硫磺的纯度为99.14%,硫酸铵中氮元素含量为23.6%.     

KINETIC STUDY OF SYNTHESIZING UNSYMMETRIC ACETALS UNDER PHASE TRANSFER CONDITIONS

An effective method was proposed to determine the two organic-phase rate constants of the primary and secondary reactions which have differences in rates. The goal was achieved by employing the reaction of two mixed l-alcohols and dibromomethane in an alkaline solution of KOH/chlorobenzene two-phase medium under phase transfer catalysis. A new product of unsymmetric acetal was obtained in this work. The intermediate ROCH₂Br (a-haloalkyl ether) was not detected during or after the reaction when using high reactive alcohols. This result indicated that ROCH2Br was more reactive than the organic reactant CH₂Br₂. This high reactive a-haloalkyl ether implied that the rate constants of secondary reactions are larger than those of the primary reactions. The resistance of mass transfer of the catalyst ((C₄H₉)₄NBr, QBr) and the active catalyst, ((C₄H₉ )₄NOR, QOR R: c₄h₉and C₈h₁₇) transferring from the aqueous phase to the organic-phase and vice versa were found to be negligible. The organic-phase reaction is a rate-determining step of the phase transfer catalytic reaction, A measured constant concentration of tetrabutylammonium alkoxide (QOR) during the reaction leads to the application of pseudo-first order rate law. The reaction rate constant of ROCh₂Br acts 10⁴ larger than that of CH₂Br₂.     

In situ FTIR study on reaction pathways in Ni(CO)4/CH3OK catalytic system for low-temperature methanol synthesis in a liquid medium

An in situ infrared spectroscopic study was conducted to elucidate the reaction pathways for low-temperature methanol synthesis in a catalytic system composed of Ni(CO)₄ and CH₃OK (denoted as Ni(CO)₄/CH₃OK). The reaction was conducted in a liquid medium at 313–333 K with an initial pressure of 3.0 MPa. When CH₃OK was added to Ni(CO)₄ solution at 293 K, different carbonylnickelates, [Ni₅(CO)₁₂]²⁻, [Ni₆(CO)₁₂]²⁻ and [Ni(CO)₃(COOCH₃)]⁻, were immediately formed from Ni(CO)₄. The species and the composition of the carbonylnickel complexes varied with temperature. The variations in concentrations of methanol (MeOH) and methyl formate (MF) during the run, which were determined from their IR absorptions, indicated a pattern characteristic of consecutive reactions with MF as an intermediate. Thus, it was shown that methanol was produced through the carbonylation of MeOH to MF and the subsequent hydrogenation of MF to MeOH. Stable hydridocarbonylnickel anions, [HNi(CO)₃]⁻ and/or [HNi₂(CO)₆]⁻, were observed together with a small amount of Ni(CO)₄ throughout the methanol synthesis. Since Ni(CO)₄ alone showed no activity for the hydrogenation of MF, the hydridocarbonylnickel anions generated in the presence of CH₃OK must be responsible for the reaction. The dual role of CH₃OK in the catalytic system was stated.     

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

The thermal dilatation in (NH₃ ·CH₃) SnCl₆, (NH₃ · C₂H₅) SnCl₆ and [N(CH₃)] SnCl₆ was measured, and as the results it has turned out that (NH₃ ⁶·C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnCl₆ undergo the first order transitions at 128 K and 158 K, respectively. The low temperature phases of (NH · C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnC1₆ are found to be monoclinic and tetragonal, respectively, No phase transition was observed in (NH₃ ·CH₃)₂ SnCl₆ down to 77 K.     

Thermodynamic behaviors of SiCl2 in silicon deposition by gas phase zinc reduction of silicon tetrachloride☆

The modified Siemens process, which is the major process of producing polycrystal ine silicon through current technologies, is a high temperature, slow, semi-batch process and the product is expensive primarily due to the large energy consumption. Therefore, the zinc reduction process, which can produce solar-grade silicon in a cost effective manner, should be redeveloped for these conditions. The SiCl2 generation ratio, which stands for the degree of the side reactions, can be decomposed to SiCl4 and ZnCl2 in gas phase zinc atmosphere in the exit where the temperature is very low. Therefore, the lower SiCl2 generation ratio is profitable with lower power consumption. Based on the thermodynamic data for the related pure substances, the relations of the SiCl2 generation ratio and pressure, temperature and the feed molar ratio nZn=nSiCl4 ? ? are investigated and the graphs thereof are plotted. And the diagrams of KpΘ–T at standard atmosphere pressure have been plotted to account for the influence of temperature on the SiCl2 generation ratio. Furthermore, the diagram of KpΘ–T at dif-ferent pressures have also been plotted to give an interpretation of the influence of pressure on the SiCl2 gener-ation ratio. The results show that SiCl2 generation ratio increases with increasing temperature, and the higher pressure and excess gas phase zinc can restrict SiCl2 generation ratio. Finally, suitable operational conditions in the practical process of polycrystalline silicon manufacture by gas phase zinc reduction of SiCl4 have been established with 1200 K, 0.2 MPa and the feed molar ratio nZn=nSiCl4 ? ? of 4 at the entrance. Under these conditions, SiCl2 generation ratio is very low, which indicates that the side reactions can be restricted and the energy consumption is reasonable.     

Searching for the active sites of Co-H-MFI catalyst for the selective catalytic reduction of NO by methane: A FT-IR in situ and operando study

A Co-H-MFI sample has been studied through FT-IR spectroscopy of in situ adsorption and co-adsorption of probe molecules (o-toluonitrile, CO, NO) and has been tested in the CH₄-SCR process under IR operando conditions. The o-toluonitrile (oTN) adsorption and the oTN and NO co-adsorption, show that both Co²⁺ and Co³⁺ species are present on the catalyst surface. Co³⁺ species are located inside the zeolitic channels while Co²⁺ ions are distributed both at the external and at the internal surfaces. The operando study show the activity of Co³⁺ species in the reaction. The existence of three parallel reactions, CH₄-SCR, CH₄ total oxidation and NO to NO₂ oxidation, has been confirmed. Isocyanate species and nitrate-like species appear to be intermediates of CH₄-SCR and NO oxidation, respectively. A mechanism for CH₄-SCR has been proposed. Co²⁺ substitutional sites, very evident and predominant in the catalyst, which are very hardly reducible, seem not to play a key role in the SCR process.     

3,3-二甲基-1-丁烯的合成工艺研究

以叔丁醇为原料,优化了其与浓盐酸氯代合成叔丁基氯的反应,采用CaCl₂ 氯化盐助催化体系使反应收率提高到95%,产品质量分数为99%;3,3-二甲基-1-丁烯合成的关键步骤是叔丁基氯与乙烯反应制备3,3-二甲基-1-氯丁烷,探讨了催化剂用量、反应温度对反应收率的影响.反应以无水三氯化铝为催化剂,用量为n(AlCl₃):n[(CH₃)₃CCl]=0.018:1,反应温度为-17~-20 ℃时,产物3,3-二甲基-1-氯丁烷的收率可达80%;最后由3,3-二甲基-1-氯丁烷脱氯化氢制备3,3-二甲基-1-丁烯.考察了不同溶剂对反应收率的影响,以聚乙二醇-400为溶剂,无需加入相转移催化剂,收率可达88.5%,3,3-二甲基-1-丁烯的质量分数为可达95%以上.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.