杂多阴离子的XPS研究——Ⅱ.Keggin 结构钨钼杂多酸热稳定性差异的研究

加入优级纯 CsCl 作内标,用其中 Cs3d_(■/2)校正荷电效应,准确地测定了 HPW_nMo_(12-n)(n=0,3,6,9,12)及 HXM_(12)(X=P,As,Si,Ge;M=W,Mo)中 Ols 及 HPM_(12)中 P2p 的结合能,发现钨系中 Ols 的结合能比钼系中的高0.5eV;P2p 的结合能则相应地高0.8eV;同种金属的磷系杂多酸中 Ols 结合能比其他杂原子中的高约0.3eV.通过差热分析发现同类型杂多酸的热稳定性与阴离子中 Ols 结合能呈近似平行的关系.结果表明,跟钼系杂多酸相比,钨系杂多酸中氧原子有较低的电子云密度,钨氧之间有更多的轨道重叠;含磷杂多酸跟其他杂多酸相比,金属、氧之间有更强的相互作用.     

杂多阴离子的XPS研究 II:Keggin结构钨钼杂多酸热稳定性差异的研究

加入优级纯CsCl作内标,用其中Cs3d5/2校正荷电效应,准确地测定了HPWnMo12-n(n=0,3,6,9,12)及HXM12(X=P,As,Si,Ge;M=W,Mo)中Ols及HPM12中P2p的结合能,发现钨系中Ols的结合能比钼系中的高约0.5eV;P2p的结合能则相应地高0.8eV;同种金属的磷系杂多酸中Ols的结合能比其他杂原子中的高0.3eV。通过差热分析发现同类型杂多酸的热稳定性与阴离子中的Ols结合能呈近似平行的关系。结果表明,跟钼系杂多酸相比,钨系杂多酸中氧原子有较低的电子云密度,钨氧之间有更多的轨道重叠;含磷杂多酸跟其他杂多酸相比,金属、氧之间有更强的相互作用。     

杂多阴离子的XPS研究 II:Keggin结构钨钼杂多酸热稳定性差异的研究

加入优级纯CsCl作内标,用其中Cs3d5/2校正荷电效应,准确地测定了HPWnMo12-n(n=0,3,6,9,12)及HXM12(X=P,As,Si,Ge;M=W,Mo)中Ols及HPM12中P2p的结合能,发现钨系中Ols的结合能比钼系中的高约0.5eV;P2p的结合能则相应地高0.8eV;同种金属的磷系杂多酸中Ols的结合能比其他杂原子中的高0.3eV。通过差热分析发现同类型杂多酸的热稳定性与阴离子中的Ols结合能呈近似平行的关系。结果表明,跟钼系杂多酸相比,钨系杂多酸中氧原子有较低的电子云密度,钨氧之间有更多的轨道重叠;含磷杂多酸跟其他杂多酸相比,金属、氧之间有更强的相互作用。     

对叔丁基杯[8]芳烃/12-钨(钼)磷(硅)杂多酸超分子包合物的合成与性质

用自识别自组装法合成了三种新型对叔丁基杯[8]芳烃/12-钨(钼)磷(硅)杂多酸超分子包合物,C88H115～116O8[XM12-040](X=P,Si;M=w,Mo),用元素分析,IR,UV,1H NMR,31P NMR,ESR,XPS,Fluorescence光谱进行了表征.结果表明,对叔丁基杯[8]芳烃主体化合物与12-钨(钼)磷(硅)杂多酸客体分子发生了主-客体包合反应,生成了稳定的发光包合物.     

磷钨杂多酸在乙醇溶液中稳定物种的研究

在M06/6-31++G(d,p),Lanl2dz的理论水平下,研究了磷钨杂多酸在乙醇中的稳定存在形式。在磷钨杂多酸中,有4种不同类型的氧原子:O_a(中心四面体里的氧原子,P-O_a)、O_b(两个三金属簇角顶共用氧原子,W-O_b-W)、O_c(同一个三金属簇共用氧原子,W-O_c-W)和O_d(端氧原子,W=O_d)。计算结果表明:在乙醇溶液中,[HPW_(12)O_(40)]~(2-)的H~+位于O_c上,[H_2PW_(12)O_(40)]~-的2个H~+均位于O_c上,H_3PW_(12)O_4的3个H~+分别位于:O_b、O_c、O_c。同时,磷钨杂多酸的最稳定物种,在298.15 K时为[H_2PW_(12)O_(40)]~-,在403.15 K时为[HPW_(12)O_(40)]~(2-)。     

磷钨钴和磷钨镍杂多酸化学修饰电极的研究

杂多酸由于组成和结构上的特点,在电化学和电分析化学领域有着广泛应用[1,2]。迄今为止,有关磷钨钴和磷钨镍三元杂多酸化学修饰电极还未见报道。本文按文献方法[3]合成了磷钨钴(Ｈ3ＰＷ11ＣｏＯ40·ｘＨ2Ｏ)和磷钨镍(Ｈ3ＰＷ11ＮｉＯ40·ｘＨ2Ｏ)杂多酸,分别以Ｈ3ＰＷ12Ｏ40·ｘＨ2Ｏ、Ｈ3ＰＷ11ＣｏＯ40·ｘＨ2Ｏ和Ｈ3ＰＷ11ＮｉＯ40·ｘＨ2Ｏ杂多酸(以下简写为Ｈ3ＰＷ11ＭＯ40·ｘＨ2Ｏ,其中Ｍ代表Ｗ,Ｃｏ和Ｎｉ)为修饰剂,采用电化学方法在导电基体玻碳(ＧＣ)电极上制备了Ｈ3ＰＷ11ＭＯ40/ＧＣ膜修饰电极,制备过程简便、快速。对膜电极的…     

新型HPWs@MIL-101催化剂的制备、表征及其催化性能

采用直接合成法将磷钨杂多酸(HPWs)固载到金属-有机骨架材料MIL-101的介孔笼中,制得新型HPWs@MIL-101多相催化剂。利用XRD、N2吸附、扫描电镜(SEM)、XPS、UV-Vis DRS、Raman和FT-IR等手段对该催化剂进行了表征,并研究了其在环戊烯选择氧化制备戊二醛反应中的催化性能。结果表明,磷钨杂多酸高度分散在金属-有机骨架MIL-101的介孔笼中,将磷钨杂多酸固载到MIL-101上后,能够很好地保持磷钨杂多酸的Keggin结构和载体MIL-101的晶体骨架结构。HPWs@MIL-101催化剂的催化性能远高于传统浸渍法制备的催化剂的催化性能,当磷钨杂多酸的负载量为12.5%(w)时,HPWs@MIL-101表现出最优的催化性能,环戊烯转化率高达100%,戊二醛的得率达到78.7%。重复实验表明该催化剂具有较高的稳定性,使用三次后,GA的得率仍然达到74.1%。     

掺杂聚吡咯钨磷钴和钨磷镍三元杂多酸的电合成及其电化学性质

电化学性能;掺杂聚吡咯钨磷钴和钨磷镍三元杂多酸的电合成及其电化学性质     

磷钨钒杂多酸对甲基丙烯酸甲酯的阻聚作用

利用DSC法测定了Dawson型和Keggin型磷钨钒杂多酸对甲基丙烯酸甲酯的阻聚效果. 研究结果表明, 对同一种杂多酸而言, 随着杂多酸样品用量的不断增加, 反应的速率常数不断减小, 阻聚性能提高. 对于不同的杂多酸而言, 随着杂多酸中钨原子与钒原子数目比例的降低, 反应的数率常数随之减小, 说明含钒原子数越多的杂多酸阻聚性能越好. 总体上, Dawson型磷钨钒杂多酸的阻聚性能要优于Keggin型的.     

Keggin结构磷钼钨杂多酸的合成及其催化氧化燃油超深度脱硫的研究

以一种新型简便的低温酸化-醚萃取法制备了一系列Keggin结构磷钼钨杂多酸催化剂,其结构和组成经FT-IR, XRD和XRF表征,并对其进行催化氧化脱硫性能研究。结果表明,控制酸化溶液pH、采用低的滴加温度是实现钼钨比可控、合成具备Keggin结构的磷钼钨杂多酸催化剂的关键。以双氧水为氧化剂,考察磷钼钨杂多酸催化剂对模拟汽油中的噻吩、苯并噻吩和二苯并噻吩的氧化性能。研究发现,随着杂多酸钼钨比的增加,催化氧化脱硫活性呈先增加后降低的趋势,其中,H₃PMo_6.1W_5.9O₄₀杂多酸的催化氧化脱硫性能最优,对废机油裂解得到的汽柴油中噻吩类有机硫的完全转化时间为12 h。     

高浓度杂多酸溶液催化性能的研究1: 一种新型异丁烷/丁烯烷 基化催化剂

在异丁烷、丁烯烷基化反应中研究了一种由杂多酸和醋酸组成的新型液体催化剂的催化性能,醋酸作为溶剂对杂多酸具有共协效应,系统研究了形成活性相的条件,杂多酸结晶水含量对活性相的形成和催化活性均有显著影响,这一催化体系具有与硫酸可比的催化活性。     

Keggin型杂多酸表面和体相的催化活性和选择性之差异的研究

本文以异丙醇脱水、甲醇转化等为模型反应,采用改变12-钨磷酸在载体SiO₂上担载量的办法,对Keggin型杂多酸催化剂进行了研究,结果表明:HPA的表面和体相酸中心,对于极性较大可进入其体相内部的异丙醇分子的脱水反应,在担载量为5×10^-5-1.5×10^-1molHPA/(dm)³SiO₂的范围内,具有相同的转化频率。HPA的表面和体相酸中心具有不同的催化选择性。     

硅钨杂多酸在中孔全硅分子筛HMS上的固载及其催化性能

用十二烷基胺代替传统的季铵盐合成了中孔全硅分子筛ＨＭＳ，并将硅钨杂多酸浸渍固载在ＨＭＳ上，用ＸＲＤ，ＦＴ－ＩＲ以及ＮＨ３－ＴＰＤ等手段对ＨＭＳ及不同负载量的焙烧温度的负载论剂进行了表征，即使在固载量为５０％的ＳｉＷ１２／ＨＭＳ中，ＳｉＷ１２仍保持其Ｋｅｇｇｉｎ结构产均匀分布在载体表面上，没有ＳｉＷ１２晶相生成，同时，在气－固相反应体系中研究了固载在ＨＭＳ上的ＳｉＷ１２在合成乙酸丁酯中的催化性能，实     

杂多酸(盐)及单缺位磷钨杂多化合物在醇类氧化反应中的催化活性

在相转移条件下,研究了杂多化合物在苄醇,环己醇氧化反应中的催化活性.六种Keggin结构杂多酸的催化活性按GeMo~12(H~4GeMo~12O~40的简写,其余类推,PW~12,PMo~12,SiMo~12,GeW~12,SiW~12顺序下降,杂多酸中的质子可分别被其它阳离逐渐取代而达到酸性修饰. H~3PW~12O~40随着其质子逐步被Na^+取代,酸性下降,催化活性大大提高;杂多酸(盐)的催化活性随体系pH值的改变将发生奇妙剧烈的变化;单缺位杂多化合物显示出较饱和杂多酸(盐)更高催化活性.溶剂对催化活性有明显影响.     

Chemical Immobilization of Heteropolyacid Catalyst on Inorganic Mesoporous Material for use as an Oxidation Catalyst

Recent progress on the chemical immobilization of heteropolyacid (HPA) catalyst on inorganic mesoporous material is reported in this review. Mesostructured cellular foam silica, mesoporous carbon, and nitrogen-containing mesoporous carbon were used as supporting materials. The mesoporous materials were modified to have a positive charge, and thus, to provide sites for the immobilization of HPA catalyst. By taking advantage of the overall negative charge of heteropolyanion, the HPA catalyst was chemically immobilized on the surface-modified mesoporous material as a charge-compensating component. Characterization results showed that the HPA catalyst was finely and molecularly dispersed on the surface of mesoporous material via strong chemical immobilization, and that the pore structure of mesoporous material was still maintained even after the immobilization of HPA catalyst. The supported HPA catalysts were applied to the model vapor-phase ethanol conversion, 2-propanol conversion, and methacrolein oxidation reactions. The supported HPA catalyst showed a better oxidation catalytic activity than the unsupported HPA catalyst in the model reactions. The enhanced oxidation catalytic performance of the supported HPA catalyst was attributed to the finely dispersed HPA catalyst, which was chemically immobilized on the positive site of mesoporous material by sacrificing its proton (Brönsted acid site). The HPA catalyst chemically immobilized on mesoporous material served as an excellent oxidation catalyst.     

Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3-hydroxypropionate anions, respectively. The as-synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]-stabilized Nb oxoclusters (Nb−OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2–3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb−OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of ⁹³Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H₂O₂ but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited “pseudo” liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.     

Esterification of n-Butanol with Acetic Acid in the Presence of H3PW12O40 Supported on Mesoporous Carbon Materials

The adsorption of H₃PW₁₂O₄₀ (HPA) from methanol solutions on mesoporous carbon supports (multiwall carbon nanotubes (CFC-3) and CFC modified with nitrogen atoms (N-CFC)) was studied. It was found that up to 10 wt % HPA was irreversibly adsorbed on the surface of CFC. This character of adsorption is indicative of the strong interaction of the adsorbate (HPA molecules) with coal surface groups (carboxylic, lactone, etc.) to form intermolecular hydrogen bonds with -electron interactions. It was found that N-containing surface centers affected the adsorption of HPA on N-CFC. The acid and catalytic properties of HPA/CFC systems in the esterification reaction of n-butanol with acetic acid were studied ([BuOH]/[HOAc] = 1 : 15 mol/mol; 80°C). It was found that the strength of proton centers, which was determined as proton affinity, decreased upon supporting HPA. The HPA/CFC-3 systems most actively catalyzed the reaction. The catalytic activity of HPA/N-CFC depended on the nature of N-containing groups at the support surface, and it decreased with concentration of pyridine-like structures.     

杂多酸的固载化─关于制备负载型酸催化剂的一般原理

杂多酸同时具有酸和氧化－还原的催化特性，有着很广泛的应用前景．这类化合物在一系列精细合成中取代硫酸作为催化剂以满足环保的要求，显示出了很大的潜力．杂多酸固载化后，不仅能在液相氧化和酸催化反应中把催化剂从反应介质中很方便地分离出来，而且还为这类均相催化反应的多相化，甚至利用催化蒸馏新工艺等创造了应有的条件，可以使生产工艺大大简化，获得更广泛的应用．本文以很好表征过的多种孔性材料，包括氧化物，如Ａｌ_２Ｏ_３、ＳｉＯ_２、ＴｉＯ_２、硅藻土、膨润土和来源不同的活性炭为载体，考察了负载杂多酸催化剂的催化活性．在大量前期工作的基础上，通过总结载体对固载杂多酸催化活性的影响等，探讨载体的内在性质在杂多酸固载、吸附和催化反应中的作用本质，为由吸附法制备各种负载型固体酸催化剂在液相中的应用提供可资参考的模型．     

Correlation between reduction potential of vanadium-containing heteropolyacid (HPA) catalysts and their oxidation activity for cyclohexanol dehydrogenation

Vanadium-containing H_6+xP₂Mo_18−xV_xO₆₂ (x = 0, 1, 2 and 3) Wells-Dawson heteropolyacid (HPA) and H_3+xPMo_12−xV_xO₄₀ (x = 0, 1, 2 and 3) Keggin HPA catalysts were applied to the vapor-phase dehydrogenation of cyclohexanol. The catalytic oxidation activity showed a volcano-shaped curve with respect to vanadium substitution for both families of HPA catalysts. The Wells-Dawson HPA showed a better catalytic oxidation performance than the Keggin HPA at the same level of vanadium substitution.     

Phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid

The phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid (HPA) system was studied. When iron salts were used with H₃PW₁₂O₄₀, the highest activity was obtained. Spectroscopic studies showed that the state of the iron ion was changed after interaction with heteropoly acid (HPA) while the Keggin structure of HPA remained. The acidic nature of HPA activated benzene to form cationic species. Insoluble iron ion-exchanged heteropoly acid was obtained by partial ion exchange method, which also showed high activity on oxidation of benzene with molecular oxygen. The effects of reaction conditions were studied and the mechanism of deactivation was discussed. For the regeneration of catalytic activity, the addition of -ascorbic acid as a reducing agent was suggested.