芳香胺盐酸盐/硼烷体系催化的氢胺化/还原反应研究

近年来有关受限路易斯酸碱对（FLPs）化学的研究受到了国内外的广泛关注,但有关芳香胺类FLPs的应用研究却极少涉及.本工作以硅烷作为还原剂,路易斯酸三（五氟苯基）硼（BCF）作为催化剂,用芳香胺盐酸盐代替苯胺,可一步反应实现炔烃与苯胺的催化氢胺化还原反应.研究发现,取代基较多的三乙基硅烷在反应中表现出较高的反应活性,吸电子取代基取代的端基芳炔的转化率也较给电子取代基取代的端基芳炔的转化率高.对催化反应的机理研究表明,胺盐与B（C₆F₅）₃及硅烷反应所生成的硼氢化芳胺盐活性中间体"[Ar₂NH₂]⁺[H-B（C₆F₅）₃]^-"的产生和分解速度决定着中间产物亚胺的生成和还原.     

B(C6F5)3催化的醛与烷氧基羟胺的一锅法还原胺化反应

近年路易斯酸B（C₆F₅）₃催化的醛酮还原及胺化反应研究表明,缺电子的路易斯酸B（C₆F₅）₃也可以作为一种"耐水"的催化剂在"有水"条件下进行催化反应.这些研究成果对进一步扩展受限路易斯酸碱对（FLPs）化学的研究领域和应用前景提供了更多可能.本文以硅烷作为还原剂,在路易斯酸B（C₆F₅）₃催化下可在温和条件下实现醛与烷基羟胺类化合物的直接还原胺化反应,并且在还原过程中N-O键不会发生断裂,可中等至高产率地制备各种烷氧基取代的羟胺衍生物.对反应机理研究发现,在中性条件下苯甲醛与苄氧基羟胺的反应仅得到缩合中间产物肟醚,而在HCl或过量H₂O的参与下苯甲醛与苄氧基羟胺的直接还原胺化均可顺利进行;对反应机理的研究表明苄氧基羟胺会与路易斯酸硼烷在过量H₂O的参与下发生质子化,在硅烷的作用下转化成具有一定还原性的"硼氢化胺盐"活性中间体并进而促使中间产物肟醚的还原.对醛与羟胺的直接还原胺化反应研究表明,在"有水"条件下路易斯酸B（C₆F₅）₃不仅仅是一种"耐水"的催化剂,在某些反应中水可能直接影响着催化反应,尤其是对醛酮的直接还原胺化反应.因此,继续深入研究有"水"条件下路易斯酸硼烷参与的催化反应机理不仅对FLPs化学的发展至关重要,对其他相应催化体系的研究也具有重要的参考价值.     

金属羰基化合物的氧原子转移反应——取代亚碘酰苯存在下Cr(CO)6的CO取代反应动力学研究

在取代亚碘酰苯存在下,研究了Cr(CO)₆与外来配体L(L=CH₃CN、PPh₃)间的羰基取代反应动力学.结果表明,该试剂的空间效应加快了反应速度,其活性顺序为:邻位取代>间位取代>对位取代>未取代;不同基团的对位取代亚碘酰苯的电子效应与氧原子转移速度之间呈良好的线性关系.吸电子基促进反应,在位阻相近的情况下,取代亚碘酰苯的活性随I-O键强减小而增大.     

离子液体促进Ru/C催化有机胺与CO_2/H_2氮甲酰化反应研究

以CO_2为甲酰化试剂和H_2为还原剂进行有机胺N-甲酰化反应是合成甲酰胺的一条绿色反应路径,具有重要意义.本工作针对有机胺与CO_2/H_2的N-甲酰化反应,构建了以1-丁基-3-甲基咪唑乙酸盐([Bmim][OAc])离子液体为溶剂、Ru/C为催化剂的非均相催化体系,在相对温和条件下(100℃、8 MPa)实现了有机伯胺、仲胺和芳香胺的N-甲酰化反应,获得了一系列甲酰胺.研究表明,[Bmim][OAc]通过与氨基形成氢键活化有机胺,并可通过调控Ru纳米粒子的电子状态,增强Ru纳米粒子对H_2的活化能力,进而实现催化N-甲酰化反应.     

1,2-双(四甲基环戊二烯基)四甲基二硅烷与六碳基钼的反应

1,2-双(四甲基环戊二烯基)四甲基二硅烷与正丁基锂作用生成(四甲基二硅撑)双(四甲基环戊二烯基负离子盐),后者随即与六碳基钼反应形成1,1'-(四甲基二硅撑)双(四甲基环戊二烯基铝负离子盐)-(Me₂SiSiMe₂)[Me₄CpMo(CO)₃-Li⁺]₂(I),I与冰醋酸作用,随即分别与CCl₄,NBS及I₂反应,生成相应的铝卤化合物(Me₂SiSiMe₂)[Me₄CpMo(CO)₃X]₂[X=Cl(1),Br(2),I(3)].I与CH₃I反应,在钼原子上发生烃基化,得到产物(Me₂SiSiMe₂)[Me₄CpMo(CO)₃Me]₂(4);I与单质I₂直接反应,生成脱硅桥产物Me₄Cp(CO)>₃I(5).经元素分析、IR及¹HNMR表征了化合物1-5的结构。     

5-取代-3,4-二卤-2(5H)-呋喃酮的Sonogashira偶联反应

以5-取代-3,4-二卤-2(5H)-呋喃酮为底物进行Sonogashira偶联反应, 考察了反应温度、反应时间、钯催化剂种类与用量、碱种类与用量、溶剂、底物结构等对偶联反应的影响, 合成了28种新的2(5H)-呋喃酮衍生物, 其结构用IR, ¹H NMR, ¹³C NMR, MS和元素分析等方法进行了表征. 在优化的反应条件下, 即反应溶剂为甲苯、催化剂为3 mol% Pd(PPh₃)₄和10 mol% CuI、碱为6 equiv. KF、反应时间72 h、反应温度30 ℃时, 反应产率42%～84%. 利用该Sonogashira偶联反应合成新型的多官能团烯二炔结构化合物, 不仅合成途径简捷、反应条件温和, 绝大部分反应产率中等以上, 而且无需额外加入配体, 适用于芳香的和脂肪的末端炔烃.     

仲胺转化为甲酰胺的接力催化（英文）

甲酰胺是重要的化工原料,广泛应用于农药和医药生产中,其合成方法备受关注.目前,主要通过胺与不同甲酰化试剂(甲酸、甲酸盐、甲酰胺和CO₂等)的N-甲酰化反应合成甲酰胺.但由于转酰化反应生成的副产物不可避免,原子经济性100%的直接甲酰化成为更理想的合成路径.典型的甲酰胺代表是N,N-二甲基甲酰胺(DMF),工业上通过CH₃OH-NaOCH₃催化剂催化二甲胺和CO直接甲酰化生成DMF.近年研究者发展了多种直接甲酰化的催化体系,例如N-杂环卡宾、KOH、K₂CO₃和Co@N掺杂碳催化剂和PdCo双金属催化剂等.本课题组也报道了Ru修饰的氧化铈(Ru/CeO₂)和羟基磷灰石(Ru-HAP)催化的胺直接甲酰化(Green Chem.,2017,19,88-92和ChemCatChem,2021,13,41594163).然而,相较于伯胺,仲胺的直接甲酰化合成甲酰胺更加困难.因此,开发一种新的仲胺转化策略进而合成高附加值的甲酰胺非常必要.本文发展了一种基于羟基磷灰石负...     

等离子体还原催化剂在CO2甲烷化反应中的活性

采用浸渍法和原位生长水滑石法制备了Ni-Ce/γ-Al₂O₃和Ni-Ce-LDHs/γ-Al₂O₃ 2种不同类型的催化剂前驱体, 考察了2种前驱体分别经氩-氢等离子体和常规氢热方法还原所得催化剂在CO₂甲烷化反应中的活性. 结果表明, 等离子体还原催化剂的低温活性明显高于常规氢热还原催化剂, 主要表现为前者反应启动的临界温度点比后者低20~30 ℃. 采用X射线衍射(XRD)分析、 透射电子显微镜(TEM)、 CO₂程序升温脱附(CO₂-TPD)以及X射线光电子能谱(XPS)对所得催化剂的形貌和结构进行了表征. 结果表明, 等离子体还原催化剂具有较小的活性组分粒径、 较高的活性组分分散度以及较高的表面碱性, 这些特性有利于催化剂活性位对CO₂的化学吸附, 使其在甲烷化反应中表现出较好的低温活性.     

CO2矿化反应基础研究 II．有机胺介质中碳酸化反应热力学研究

对有机胺介质中CaCl₂与二氧化碳的碳酸化反应进行了研究,在二氧化碳压力为2MPa~5MPa、CaCl₂浓度为1.31mol/L~2.44mol/L下考察了压力和浓度对该多相反应体系碳酸钙收率和有机胺萃取效率的影响。结果表明,碳酸化反应过程中碳酸钙收率和有机胺萃取效率随二氧化碳压力和CaCl₂初始浓度的增大而增加。结合Pitzer电解质溶液模型、二氧化碳溶解模型对该多相反应进行热力学平衡分析。有机胺的萃取平衡决定了HCl在有机相和水相的分配平衡,水相中H⁺浓度限制H₂CO₃解离,制约碳酸钙沉淀反应。CaCl₂浓度大小影响了HCO₃^-和CO₃²-的活度系数,对沉淀/溶解平衡也有一定影响。热力学平衡转化率与实验结果接近,表明该反应受化学反应平衡控制。     

铁基催化剂在COx加氢制高附加值烃反应中的应用

化石燃料的广泛使用导致大气中CO₂的排放量急剧增加,进而引起全球变暖和海洋酸化等一系列问题.CO加氢(费托合成)反应是利用非石油来源的原料生产液体燃料和化学品的一种重要途径.同时,利用可再生的H₂将CO₂转化为高附加值的产品有利于减少对化石燃料的依赖,减轻由于大气中CO₂浓度过高带来的负面影响.开发新型、高效、稳定的催化剂是费托合成和CO₂加氢制高附加值烃的关键因素之一.Fe基、Co基和Ru基催化剂是费托合成中常用的催化剂.而在CO₂加氢反应中,Co基和Ru基催化剂上主要发生甲烷化反应,几乎没有长链烃生成.Fe基催化剂在费托合成和CO₂加氢反应中均表现出优异的催化生成长链烃性能.同时,Fe储量丰富和价格便宜的特点也促进Fe基催化剂在两个反应中的广泛应用.一般认为,在Fe基催化剂上CO₂通过逆水煤气变换反应生成CO,CO通过费托合成反应继续加氢生成烃类.因此,CO₂加氢反应和费托合成反应有相似之处,同时也有较大的区别.本文从活性相、助剂和载体的角度综述了各组分在Fe基催化剂催化CO/CO₂加氢反应中的作用,总结了其中的区别与联系.催化剂在反应中会发生复杂的相变过程,形成多种铁物种;其中,碳化铁(χ-Fe₅C₂,ε-Fe₂C,Fe₇C₃和θ-Fe₃C)在费托合成反应中是C-C偶联的活性相,但对于θ-Fe₃C现还存在一些争议.在CO₂加氢反应中Fe₃O₄催化逆水煤气变换反应,碳化铁催化CO加氢反应.金属助剂对CO/CO₂加氢反应的促进作用较为相似,在两个反应中碱金属的促进作用最为明显.费托合成反应对载体有较强的适应性,而CO₂加氢反应对载体敏感性较强,Al₂O₃,ZrO₂和碳材料载体效果较好.本文还总结了近些年来基于对活性相、助剂和载体的深入理解设计制备的一些新型催化剂及其在费托合成和CO₂加氢反应中的应用,包括具有新颖结构的催化剂、金属-有机骨架衍生催化剂以及与沸石分子筛结合的双功能催化剂.最后,还分析了目前Fe基催化剂在费托合成和CO₂加氢反应应用中所面临的问题和挑战,并对未来的发展趋势进行了展望.     

CH4+CO2H2+CO

将廉价的碳源(CO2)转化为化石燃料可缓解由于温室气体引起的气候问题.CH4/CO2重整(CRM)是CO2转化利用的有效途径之一,要实现这个过程的关键是研制高效的光响应催化剂.本文采用WO3负载的第VIII族金属催化剂、引入光照能量来活化CO2,利用光热协同催化CRM.研究结果表明,光学材料WO3负载的第VIII族金属催化剂在可见光辅助下的催化活性是热驱动条件下的1.4～2.4倍,与等离子体金催化剂的活性增强率(1.7倍)相当.进一步以不同波段的可见光为光源,对WO3负载的第VIII族金属催化剂上催化活性提高的原因进行了研究.结果表明,活性增强率与WO3在可见光区域的吸光趋势并不吻合,说明并非WO3提高了其负载的第VIII族金属催化剂上CRM活性.除WO3外, WO3-x亦可作为光催化剂吸收可见光,因此,本文通过X射线光电子能谱、X射线衍射及紫外-可见分光光度法等进行表征.结果表明,在还原型CRM反应气氛下, WO3部分原位还原为WO3-x,并且活性增强率与WO3-x在可见光区域的吸光趋势相吻合,说明导致可见光辅助下活性增强的是WO3-x而不是WO3.热力学分析及原位电子顺磁共振波谱法结果表明, CO2的活化是CRM的速控步,该步骤吸热,在500 oC时不能自发进行.在可见光的辅助下, CO2可以被WO3-x通过Mars-vanKrevelen机理进行活化,提高速控步的反应速率,进而提高了催化活性.综上,本文为提高光催化活性提供了一条有效途径.     

Hydrocondensation of CO2

New bis(diphenylphosphino) methane, (dpm) complexes of palladium have been prepared from PdCl₂dpm, either by borohydride reduction or halide abstraction in the presence of added ligand. The catalytic activities of these and other polynuclear palladium and copper complexes in the CO₂/H₂ reaction have been tested. The result confirm the catalytic formation of alkyl formate and dialkyl formamide, but the juxtaposition of two or more metal centres does not appear to promote the catalytic formation of C₂-compounds (oxalate)     

Interaction of O2, CO and CO2 with Co films

Metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS(HeI)) and x‐ray photoelectron spectroscopy (XPS) were applied to study the interaction of O₂, CO and CO₂ with Co films at room temperature. The films were produced on Si(100) surfaces under the in situ control of MIES, UPS and scanning tunnelling microscopy (STM). For O₂, dissociative adsorption takes place initially and then incorporation of oxygen starts at exposures of ～5 L. Comparison of the MIES and UPS spectra with those published for CoO shows that near‐stoichiometric CoO films can be obtained by co‐deposition of Co and O₂. The CO is adsorbed molecularly up to a maximum coverage of ～0.6 monolayer, with the C‐end pointing towards the surface. The CO₂ adsorption is dissociative, resulting in the formation of Co–CO bonds at the surface. The resulting oxygen atoms are mostly incorporated into the Co layer. For all studied molecules the interaction with Co is similar to that with Ni. Copyright © 2005 John Wiley & Sons, Ltd.     

Carbon Isotope Fractionation during the Formation of CO2 Hydrate and Equilibrium Pressures of 12CO2 and 13CO2 Hydrates

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO₂ hydrates. We investigated carbon isotope fractionation during CO₂ hydrate formation and measured the three-phase equilibria of ¹²CO₂–H₂O and ¹³CO₂–H₂O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound ¹²CO₂ and ¹³CO₂ was revealed, although their unit cell size was similar. The δ¹³C of hydrate-bound CO₂ was lower than that of the residual CO₂ (1.0–1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in ¹²CO₂ and ¹³CO₂ hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the ¹²CO₂–H₂O and ¹³CO₂–H₂O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.     

Oxidising CO to CO2 using ceria nanoparticles

We calculate, using simulated amorphisation and recrystallisation (A&R), that ceria (CeO2) nanoparticles, about 8 nm in diameter, comprise a high concentration of labile surface oxygen species, which we suggest will help promote the oxidation of CO to CO2. In particular, the ceria nanoparticle contains a high proportion of reactive {100} surfaces, surface steps and corner sites. When reduced to CeO1.95, the associated Ce3+ species and oxygen vacancies decorate step, corner and {100} sites in addition to plateau positions on {111}. The energetics of CO oxidation to CO2, catalysed by a ceria nanoparticle, is calculated to be lower compared with CO oxidation associated with the lowest energy surface (i.e. CeO2(111)) of the corresponding 'bulk' material. Our calculated morphologies for the ceria nanoparticles are in accord with experiment.     

Raman investigation of the CO2 complex formation in CO2-acetone mixtures

Polarized and depolarized Raman spectra of CO2-acetone mixtures have been measured along the isotherm 313 K as a function of CO2 concentration (0.1-0.9 molar fractions in CO2) by varying the pressure from 0.2 up to 8 MPa. Upon CO2 addition, a new band appears at about 655 cm(-1) and is assigned to the lower frequency nu 2(1) component of the bending mode after degeneracy removal due to the formation of a 1:1 electron donor acceptor (EDA) CO2 complex. The equilibrium constant associated with the complex formation was estimated and found close to those of contact charge transfer complexes. The main modifications of the Fermi dyad of CO2 in the mixtures compared with that of pure CO2 at equivalent density have been assessed. The band-shape analysis revealed that each dyad component is described by two Lorentzian profiles, showing that a tagged CO2 molecule probes two kinds of environment in its first shell of neighbors. The first one involves nonspecific interactions of CO2 with surrounding acetone whereas the second is assigned to the signature of 'transient' CO2 complexes formed with acetone. An upper bound life time of the complex has been estimated to be 8 ps. In addition, a broad band has been detected between the Fermi dyad peaks at about 1320 cm(-1) and its origin interpreted as a further evidence of the CO2-acetone heterodimer formation. Finally, the values of the equilibrium concentration of the heterodimer versus the total concentration of CO2 deduced from the analysis of the nu 2(1) band and from the Fermi dyad have been compared, and the difference is interpreted as due to a lack of theoretical approach of Fermi resonance transitions associated with species existing in different environments.     

A cross-association model for CO2-methanol and CO2-ethanol mixtures

A cross-association model was proposed for CO₂-alcohol mixtures based on the statistical associating fluid theory (SAFT). CO₂ was treated as a pseudo-associating molecule and both the self-association between alcohol hydroxyls and the cross-association between CO₂ and alcohol hydroxyls were considered. The equilibrium properties from low temperature-pressure to high temperature-pressure were investigated using this model. The calculated p-x and p-ρ diagrams of CO₂-methanol and CO₂-ethanol mixtures agreed with the experimental data. The results showed that when the cross-association was taken into account for Helmholtz free energy, the calculated equilibrium properties could be significantly improved, and the error prediction of the three phase equilibria and triple points in low temperature regions could be avoided.