溶剂化效应对金属-有机骨架材料界面微环境催化性能的影响

金属-有机骨架材料(metal-organic frameworks,MOFs)的纳微结构可根据特定需求进行功能化调控,有望成为良好的工业催化材料。由于溶剂环境可对其界面微环境及催化性能产生较大影响,因此研究溶剂化效应对于MOF材料的影响具有重要的意义。以Cu-BTC和MOP-15两种典型MOF材料作为研究对象,采用密度泛函理论与COSMO溶剂模型相结合的方法,考察了溶剂效应对材料几何结构与电子稳定性的影响,并研究了不同溶剂对其Lewis酸性的影响。结果表明,溶剂环境可以使材料中的电子从不饱和配位金属处转移到有机配体上,进而使材料具有更强的Lewis酸性,并且电负性较大有机配体构成的MOF材料,受溶剂效应的影响更加显著。本工作将有助于深入理解溶剂化对调控MOF材料液相催化活性的影响。     

氨基酸金属有机框架的研究进展

氨基酸金属有机框架是指含有氨基酸单元的有机配体与金属离子共同参与合成的具有周期性结构的材料。氨基酸作为蛋白质的组成成分,具有绿色环保、生物相容性良好、种类多样、价格低廉等优点,将其引入金属有机框架(MOF)可以赋予材料特殊的柔性结构、丰富的活性位点、优良的应用性能等特征,因而引起了研究人员浓厚的兴趣。综述首先阐述了氨基酸MOF的结构维度分类;其次说明了氨基酸MOF的主要合成方式包括溶剂热法、机械化学合成法、微波加热辅助法;然后进一步讲解了材料的性能调控;在此基础上重点介绍了这类材料在手性拆分、催化、吸附等领域的应用;最后,通过分析当前氨基酸金属有机框架材料存在的材料稳定性不好、结构难以预测等问题,对其未来在生物医药领域的研究重点进行了展望。     

Lewis酸碱位点共存的MOFs在CO_2环加成反应中的催化应用

二氧化碳(CO2)是一种温室气体,同时也是丰富、无毒、不燃的可再生碳一资源,其转化和利用具有重要意义,CO2与环氧化物环加成反应制备环状碳酸酯就是其中一种具有研究价值的途径。金属有机骨架材料(MOFs)由于具有可设计的模块化结构,在催化等领域一直以来都是研究热点。通过选择合适的有机配体与金属中心组装可以得到同时含有Lewis酸、碱位点的MOFs材料,能够在无助催化剂无溶剂条件下催化CO2环加成反应。本文将以MOFs材料中Lewis酸、碱位点的类型为出发点来介绍含Lewis酸-碱对MOFs材料催化CO2环加成的相关工作。     

Zr系列MOFs催化乙酸乙酯N-酰胺化反应

以二氯氧锆（ZrOCl₂）和不同的有机配体，如对苯二甲酸、均苯三甲酸、1,2,4-苯三甲酸和1,2,4,5-苯四甲酸为原料，采用溶剂热法合成了一系列Zr基金属-有机框架（Zr-MOFs）材料。利用X射线粉末衍射（XRD）、氮吸附脱附等温线、傅里叶变换红外光谱（FTIR）、热重分析（TGA）和扫描电子显微镜（SEM）对材料进行一系列表征。以乙酸乙酯与苯甲胺反应转化为N-乙酰苄胺为模型反应，研究所得Zr-MOFs材料的催化性能。结果表明，Zr-MOFs材料的催化活性可以通过改变有机配体中羧酸基团的数目和位置来调控，有机配体中羧基数目主要影响Zr-MOFs材料的晶体结构以及Lewis酸性和Br?nsted酸性，从而影响催化活性。相同条件下，具有MOF-808晶体结构的Zr-MOF材料催化活性最高，80℃反应12h，N-乙酰苄胺的产率高达95%。此外，该催化剂具有良好的循环使用稳定性，重复使用5次后，N-乙酰苄胺的产率仍保持90%。     

镁-三苯胺基MOF的制备及光/Lewis酸协同催化

利用水热法将具有Lewis酸性的Mg2+ 和光敏性的三苯胺三羧酸（H3TCA）自组装，构筑了金属有机框架（metal-organic framework; MOF）Mg-TCA，并通过SC-XRD表征了其晶体结构。UV-vis、FL、CV等测试表明Mg-TCA在可见光区（> 400 nm）具有良好的吸收，其激发态氧化还原电位为-1.95 V (vs. SCE)。以苯乙烯类化合物（0.2 mmol）为底物，NHPI活性酯（0.3 mmol）为自由基前体，Mg-TCA（0.01 mmol）为催化剂，DMSO（2 mL）为溶剂和氧化剂，氮气保护，在405nm的LED下照射24 h，反应以30%~82%的产率生成相应的α-烷基苯乙酮。催化剂Mg-TCA可以重复使用3次并且仍保持活性和晶态结构。机理研究表明在反应过程中发生了光/Lewis酸协同催化，Mg-TCA中具有Lewis酸性的镁节点对NHPI活性酯的吸附作用拉近了其与光催化中心三苯胺的距离，从而提升了催化反应的效率。     

UiO-66(Zr)系列MOFs 催化材料的制备及在乳酸乙酯合成中的应用

以无水四氯化锆ZrCl₄和不同的有机配体,如苯二甲酸、2-硝基苯二甲酸和1,2,4-苯三甲酸为原料,DMF为溶剂,通过溶剂热法合成了一系列UiO-66(Zr)的金属有机骨架MOFs,并用于催化转化二羟基丙酮至乳酸乙酯的反应。UiO-66(Zr)的催化活性和乳酸乙酯的选择性可以通过在制备过程中采用含有不同吸电子基团的无机配体来调节。而且当使用反应中间产物丙酮醛作为起始反应物时,MOFs的活性有了显著的提高。材料表征结果显示,UiO-66(Zr)系列MOFs材料中Brønsted酸的含量低但强度较大,而Lewis酸的含量则较高。本文对二羟基丙酮转化为乳酸乙酯的反应机理进行了详细分析,并实现了100%的二羟基丙酮转化率和乳酸乙酯选择率。     

ZnCo双金属MOF材料的制备及其催化性能探究

以(CH3COO)2Zn和(CH3COO)2Co为金属源,咪唑为有机配体,采用一锅法合成ZnCo双金属节点的金属有机骨架(Metal Organic Frameworks,MOF),将制备的材料用于活化过硫酸盐降解罗丹明B以评估其催化性能.结果 显示考所制备的材料具有优异的催化性能,且受pH影响小,在罗丹明B、过一硫酸...     

负载金属的ZIF-8催化活性的计算化学研究

金属-有机骨架材料(metal-organic frameworks,MOFs)是一类新型纳米多孔功能材料。由于其独特的结构特征,在催化方面展现出潜在的应用价值。采用分子模拟结合密度泛函理论的计算方法系统地研究了ZIF-8在负载金属Pd、Ag、Pt、Au后的催化活性。结果表明,金属与材料之间主要有3种作用方式,其中以"碳-金属-碳"(C-M-C)形式最为稳定。并且对于同一种方式,ZIF-8负载金属后的稳定性顺序为:PdAgPtAu。同时,利用CO作为探针分子,系统地研究了负载金属后ZIF-8的催化活性,发现这些金属原子的Lewis酸性强弱与其电子接受能力有关,其催化活性顺序为:PdPtAgAu。这为研究利用MOF材料负载金属用于催化提供了参考信息。     

金属有机骨架材料固载金属催化剂的应用

金属有机骨架材料(MOFs)作为一类配位聚合物,具有孔洞结构、高比表面和独特的化学调变性。其中通过有机配体的选择,可以设计将不同的金属有机配合物分子固定在MOF孔道内部,从而使得材料具有开放而独立的催化位点。本文对金属有机骨架材料(MOFs)在固载金属催化剂的应用进行了简要概述。     

PS负载乙二胺系列钼配合物催化环己烯环氧化的反应性能

以大孔聚苯乙烯树脂为载体,乙二胺(en)、二乙烯三胺(dien)及三乙烯四胺(trien)为配体,合成了PS-en-Mo(Ⅵ)、PS-dien-Mo(Ⅵ)以及PS-trien-Mo(Ⅵ)催化剂,并对其进行了结构表征,IR谱证实已在PS载体完成对目的物的负载;XPS谱的结果表明,所合成的以上3种Mo配合物中的钼皆以Mo(Ⅵ)价态形式存在,据此提出了所合成高分子金属配合物的可能结构。PS负载乙二胺系列钼配合物在催化t-BuOOH环氧化环己烯反应中,都具有很高催化活性,但随着配体分子中N原子个数的增加,催化选择性降低明显。认为这是N原子配位能力强,供电能力高,与Mo配位后形成的Mo—N键,大大减低了Mo的正电性,使Mo的Lewis酸性降低,从而使Mo(Ⅵ)活性中心与t-BuOOH形成金属双氧活性中间体的能力下降所致。配体分子N原子的增加,碱性增强,不仅进一步减低Mo的Lewis酸性,且会使t-BuOOH分解,最终导致选择性降低严重。     

酸性离子液体催化苯胺和二氧化碳合成二苯基脲

以苯胺和二氧化碳为原料催化合成二苯基脲是一条绿色工艺路线,重点对Lewis酸类离子液体催化该反应性能进行了研究。考察了一系列碱性和Lewis酸性催化剂的催化性能,以及溶剂对该反应的影响,结果表明,以无水AlCl₃为催化剂和乙腈为溶剂组成的反应体系效果较好。以氯铝酸类离子液体为催化剂兼溶剂,考察了离子液体阴阳离子、CO₂初始压力、反应时间、反应温度以及催化剂用量等因素对二苯基脲合成反应的影响。结果表明,以［Bmim］Cl-AlCl₃离子液体为催化剂兼溶剂,在CO₂初始压力为1 MPa、反应时间为7 h、反应温度为160℃、AlCl₃/苯胺质量比为1∶1的条件下,苯胺的转化率、二苯基脲的收率及选择性分别为18.1%、17.9%和98.9%。此外,提出了［Bmim］Cl-AlCl₃离子液体催化苯胺和二氧化碳的反应机理。     

H-ZSM-5分子筛催化剂上乙醇脱水合成乙醚的研究

乙醇是一种重要的生物质平台分子,而乙醚是一种具有广泛用途的化学品,因此将乙醇高效脱水合成乙醚受到了广泛的关注。文章通过在不同温度下处理H-ZSM-5分子筛,获得了一系列比表面和晶型类似,而Brnsted酸位点比例不同的催化剂。进一步研究发现,催化剂单位酸位点脱水活性随着Brnsted酸位点比例下降而线性下降。所以我们认为在催化乙醇脱水合成乙醚的反应中,Brnsted酸位点起主要作用。     

Polar attributes of supercritical carbon dioxide

Supercritical carbon dioxide (scCO(2)) is increasingly promoted as an environmentally benign alternative to conventional organic solvents. The supercritical state bridges the gap between liquid and gaseous states by offering gaslike diffusion rates and liquidlike solvent densities, thereby enabling potential opportunities as a reaction and separation medium in chemical industry. Understanding the solvent behavior of liquid and scCO(2) is of critical importance to enable the design of CO(2)-philic molecular systems and to expand the use of these solvent systems to a wider range of chemical processes. Historically CO(2) was treated as a nonpolar solvent, primarily because of its low dielectric constant and zero molecular dipole moment. CO(2) has also been described as a quadrupolar solvent because of its significant quadrupole moment. Recent studies suggest that, as far as the microscopic solvent behavior of CO(2) is concerned, CO(2) has the potential to act as both a weak Lewis acid and Lewis base. Also, strong theoretical and experimental evidence indicates that CO(2) can participate in conventional or nonconventional hydrogen-bonding interactions. All of these site-specific solute-solvent interactions are important to understand the fundamental nature of CO(2) as a solvent. In this Account, we discuss these polar attributes of CO(2) and their relation to solvation.     

Dispersion of Silicon Carbide Powders in Nonaqueous Solvents

Thirty-two pure solvents were used to disperse laser-synthesized SiC powder, oxidized laser-synthesized SiC powder, and commercially available SiC powder. Five-day sedimentation tests were used to screen the solvents. Relative turbidity of the supernatant after 1 month was used as a quantitative measure of the degree of dispersion. Coagulation kinetics were measured by photon correlation spectroscopy to determine the coagulation rate. Stabilized powders were centrifugally cast into ceramic green bodies and their green densities measured. Experimental dispersion results were correlated with various solvent properties including dielectric constant, hydrogen-bond index, acid dissociation constant (p K _a), and Lewis acid/base interaction energy. Microcalorimetry was used to measure the heat of wetting of the powders in various acidic and basic solvents. The heat of wetting was used to determine the Lewis interaction energy parameters for the powder surfaces. Oxidized SiC powder, either laser or commercial, was shown to have an acidic surface and was stabilized by basic solvents. Pure laser-synthesized SiC powder was shown to have a basic surface and was stabilized by acidic solvents. Solvents with high hydrogen-bond indices gave high packing densities. Other solvent properties had a much smaller influence on powder dispersibility. Good dispersibility gave ceramic green bodies with high green densities.     

负载金属的ZIF-8催化活性的计算化学研究

金属-有机骨架材料（metal-organic frameworks,MOFs）是一类新型纳米多孔功能材料。由于其独特的结构特征,在催化方面展现出潜在的应用价值。采用分子模拟结合密度泛函理论的计算方法系统地研究了ZIF-8在负载金属Pd、Ag、Pt、Au后的催化活性。结果表明,金属与材料之间主要有3种作用方式,其中以“碳-金属-碳”（C-M-C）形式最为稳定。并且对于同一种方式,ZIF-8负载金属后的稳定性顺序为：Pd >Ag >Pt >Au。同时,利用CO作为探针分子,系统地研究了负载金属后ZIF-8的催化活性,发现这些金属原子的Lewis酸性强弱与其电子接受能力有关,其催化活性顺序为：Pd >Pt >Ag >Au。这为研究利用MOF材料负载金属用于催化提供了参考信息。     

Defective NH2-UiO-66 (Zr) effectively converting CO2 into cyclic carbonate under ambient pressure,solvent-free and co-catalyst-free conditions

In this study, a series of metal–organic frameworks (MOFs) NH₂-UiO-66-xHAc catalysts were synthesized by solvothermal method using acetic acid (HAc) as a modulator, and were applied to the cycloaddition of CO₂ and epichlorohydrin (EPIC) under ambient pressure. Influences of the modulation by HAc on morphologies and structures of the MOFs are demonstrated via PXRD, FESEM, FTIR, N₂ adsorption–desorption, XPS and ¹H NMR characterizations. The results show that the MOFs containing mesoporous pores can be prepared by adjusting the concentration of HAc. By optimizing the amount of HAc added, the specific surface area of NH₂-UiO-66-8HAc is as high as 879.17 m²·g^-1, which is 28.3% higher than that of the original MOFs. And the evaluation of catalytic performance showed that HAc modulation enhanced the activity of NH₂-UiO-66-xHAc under mild conditions. The exposure of Lewis acid sites, increased specific surface area and porosity via the modulation of HAc defective ligand can be supposed the key factors to determine the enhanced catalytic activities. In addition, considering the influence of gas concentration on the reaction, the concept of TOP (Turnover of Pressure, defined as the mass of conversions of a unit mass catalyst under unit pressure and unit time) was first proposed in this article.     

Influence of Solvent on Reaction Path to Synthesis of Methyl N-Phenyl Carbamate from Aniline,CO2 and Methanol

Methyl N-phenyl carbamate （MPC）, an important organic chemical, can be synthesized from aniline, CO2 and methanol. Catalyst Cu-Fe/ZrO2-SiO2 was first prepared and its catalytic performance for MPC synthesis was evaluated. Then the influence of solvent on the reaction path of MPC synthesis was investigated. It is found that the reaction intermediate is different with acetonitrile or methanol as a solvent. With acetonitrile as a solvent, the synthesis of MPC follows the reaction path with diphenyl urea as the intermediate, while with methanol as a solvent the reaction occurs via the reaction path with dimethyl carbonate as the intermediate. The catalytic mecha-nism of cooperative catalysis comprising metal sites, Lewis acid sites and Lewis base sites is proposed according to different reaction intermediates.     

Evaluation of strong acid properties of layered HNbMoO6 and catalytic activity for Friedel–Crafts alkylation

The acid properties and catalytic activity of layered HNbMoO₆ for liquid-phase Friedel–Crafts alkylation are examined. ³¹P MAS NMR spectroscopy using trimethylphosphine oxide as a probe molecule reveals that HNbMoO₆ possesses strong acid sites in the interlayer region. Layered HNbMoO₆ is demonstrated to display remarkable catalytic performance for this reaction, substantially exceeding the activities of niobic acid, niobium–molybdenum mixed oxide, ion-exchange resins, and zeolites. It is determined that benzyl alcohol is intercalated into the HNbMoO₆ interlayer during alkylation to form a monolayer configuration, allowing the strong interlayer acid sites to participate in the reaction.     

造纸污泥基固体酸催化D-果糖转化5-羟甲基糠醛

以含有丰富金属离子的造纸污泥为原料，通过高温煅烧法制备生物炭（SBC），并与对氨基苯磺酸进行接枝，制备了一种高效碳基固体酸催化剂（S-SBC）。通过FTIR、XRD、SEM等对催化剂的组成、形貌、结构、酸负载量、比孔径及比表面积等进行表征。将该催化剂用于D-果糖转化为5-羟甲基糠醛（HMF）反应，对反应时间、反应温度、催化剂用量及溶剂种类、D-果糖质量分数等影响因素进行考察，并与用杨木为原料且采用相同方法制备的杨木炭催化剂（S-PBC）进行比较，结果表明，S-SBC的催化活性优于S-PBC。S-SBC同时含有由金属离子形成的Lewis酸位点以及—SO3H等形成的Brönsted酸位点，两种酸位点在催化D-果糖脱水制备5-羟甲基糠醛的过程中具有协同作用。S-SBC在二甲基亚砜中130 ℃下催化反应40 min， HMF收率高达95.2%。连续使用4次后，催化活性没有明显下降。     

Development of novel Lewis acid catalysts for selective organic reactions in aqueous media

New types of Lewis acids as water-compatible catalysts have been developed. Various metal salts were found to work as Lewis acid catalysts in aqueous media, and catalytic asymmetric aldol reactions in such media have been attained. Furthermore, Lewis acid-surfactant combined catalysts, which can be used for reactions in water without using any organic cosolvents, have been also developed. These investigations will contribute to reducing the use of harmful organic solvents and to develop efficient catalytic systems which cannot be realized in conventional organic solvents.