PW_(11)M(M=Cu、 Co)@TiO_2多相催化剂的制备及氧化脱硫性能

以过渡金属(Cu, Co)取代磷钨酸为模板剂,硫酸钛为钛源,通过一步模板法合成出一类多酸基PW_(11)M(M=Cu、 Co)@TiO_2材料,采用FT-IR、 XRD、 XPS、 Raman、 SEM和TEM表征手段对材料进行了结构表征.结果表明, PW_(11)M(M=Cu、 Co)被引入到TiO_2中,形成了球形核壳结构. N_2吸附-脱附测试表明, PW_(11)Co@TiO_2具有介孔结构:孔径大小为3.3 nm,比表面积为72.4 m~2/g.在以H_2O_2为氧化剂,乙腈为溶剂的氧化脱硫反应体系中考察了其催化活性,结果表明:复合材料PW_(11)M(M=Cu、 Co)@TiO_2表现出良好的催化性能.其中催化剂PW_(11)Co@TiO_2在投入量为40 mg,反应底物为500 ppm,反应温度60℃,反应40 min后, DBT的脱硫率达到99.7%.中断和循环实验表明,催化剂PW_(11)Co@TiO_2具有良好的稳定性,在相同的反应条件下,循环反应5次后,催化剂的催化活性没有明显下降.     

第四周期过渡金属钨磷杂多酸盐的合成及表征(C)

合成了Keggin型缺位取代杂多酸盐(Na5PW11Z(H2O)O39,Z=Mn、Fe、Co、Ni、Cu、Zn,以下简称PW11Z)催化剂.通过ICP、IR、UV等表征手段对催化剂进行了表征.元素分析结果表明,各缺位取代杂多酸盐的计量式为Na5PW11Z(H2O)O39.IR光谱表明,取代型杂多化合物仍保持Keggin型骨架结构.而且,除了Na5PW11Ni(H2O)O39以外,其余化合物的P-O键吸收峰发生劈裂,其劈裂强度为PW11Cu>PW11Zn>PW11Mn>PW11Fe>PW11Co.Mo=O键的振动向低波数位移.UV表征结果表明,由于过渡金属的引入,相对于Keggin型杂多酸H3PW12O40,取代产物的紫外可见吸收峰向紫外方向位移,但位移强度不大,基本有与H3PW12O40中Mo=O键的ππ*跃迁大致相同的吸收.还利用以上催化剂对正己醇氧化生成正己醛的反应活性进行了考察.     

单过渡金属配位磷钨酸铵盐的合成及其催化环己酮氨肟化

以磷钨酸和过渡金属盐在pH值为4.0~5.0的条件下合成了4种具有Keggin结构的单过渡金属配位磷钨酸铵盐NH4MPW11(M=Zr2+,Co2+,Ni2+,Cu2+),通过红外、紫外、热重、X射线衍射、循环伏安法等技术对这类杂多化合物的结构和性质进行了表征,并考察了它们在环己酮氨肟化反应中的催化性能.结果表明:单过渡金属配位的磷钨酸铵盐NH4MPW11(M=Zr2+,Co2+,Ni2+,Cu2+)具有典型的Keggin结构,过渡金属离子配位后,热稳定性和氧化性增强;在催化环己酮氨肟化反应中,NH4MPW11的催化性能低于单缺位磷钨酸铵盐(NH4PW11),其中NH4ZrPW1 1为催化剂,性能优于M=Co2+,Ni2+,Cu2+的催化剂,环己酮的转化率达到85.1%,环己酮肟的选择性达到92.1%,而NH4CuPW11的催化性能则下降显著;H2O2的分解实验表明,过渡金属配位的磷钨酸铵盐对H2O2分解均存在一定的促进作用,分解能力随过渡金属种类而变化,其中NH4CuPW1 1对H2O2的分解率高达72.3%,这是造成过渡金属配位的磷钨酸铵盐在环己酮氨肟化反应中催化性能下降的主要原因;回收催化剂的红外和XRD表征表明,氨肟化反应后的NH4MPW11保持了Keggin型的一级结构,但二级结构遭到一定程度的破坏.     

模板法制备催化剂PW12@Fe-TiO2及其催化氧化脱硫性能

采用模板法一步合成了一类多酸基PW_(12)@Fe-TiO_2材料,利用Raman、XRD、XPS和SEM表征手段对材料进行了结构表征。结果表明,磷钨酸(PW_(12))被包埋到Fe-TiO_2中,形成球形结构。N_2吸附-脱附测试显示,PW_(12)@Fe-TiO_2为介孔材料:孔径尺寸为4.1 nm,比表面积为30.3 m~2·g~(-1)。所合成材料作为催化剂,以H_2O_2为氧化剂,乙腈为溶剂,在模拟油的氧化脱硫反应体系中表现出较好的催化性能。当PW_(12)@Fe-TiO_2的加入量为40 mg,反应底物为5.0 mL,反应温度60 ~oC,反应到40 min时,DBT的去除率到达了99.9%。中断和循环实验结果表明,催化剂PW_(12)@Fe-TiO_2具有良好的稳定性,在相似的反应条件下,循环使用5次,催化剂的催化活性依然保持不变。     

氨基化磁性Fe3O4@Cu3(BTC)2材料的合成及其在Knoevenagel缩合中的催化性能

金属有机骨架材料具有大比表面积、高孔隙率、热稳定性好、规整且可调控的孔结构、易于功能化的骨架金属离子和有机配体等优点,是制备多相催化剂的重要材料之一.虽然减小金属有机骨架材料等多孔材料的粒径可以提高反应物的传质效率,从而提高其催化活性;但是,纳米尺寸催化剂的分离和回收困难.将磁性纳米粒子和金属有机骨架材料结合制备具有核-壳结构的磁性金属有机骨架材料是解决上述问题的有效方法.此类材料兼具磁性材料和金属有机骨架材料的双重优势,既可以磁性分离,又具有金属有机骨架材料的催化活性.而且,厚度可控的壳层材料表现出与纳米催化剂相当甚至更好的催化活性.我们采用逐层自组装方法制备了核-壳结构的磁性Fe3O4@Cu3(BTC)2复合材料,并对材料进行氨基化修饰,制备了基于金属有机骨架材料的磁性多相碱催化剂.采用粉末X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、透射电镜(TEM)、扫描电镜(SEM)、氮气吸附等方法对材料的组成和结构进行了表征,并考察了材料在Knoevenagel缩合反应中的催化性能.首先采用粉末XRD表征材料的晶体结构.在复合材料Fe3O4@Cu3(BTC)2的XRD谱中,同时出现了Fe3O4和Cu3(BTC)2的特征衍射峰.采用氨基配体修饰后,材料的XRD谱没有明显变化,说明修饰后的材料保持了Fe3O4@Cu3(BTC)2的晶体结构.透射电镜结果表明,包裹25次得到的磁性复合材料Fe3O4@Cu3(BTC)2是以Fe3O4为核心,以Cu3(BTC)2为壳的核-壳结构,壳层厚度大约为200 nm.氨基修饰后,材料的透射电镜图相对修饰前无明显变化.扫描电镜结果表明,合成的Fe3O4为球形结构,粒径为100-600 nm.采用Cu3(BTC)2进行包裹后,在Fe3O4表面生长了由Cu3(BTC)2纳米颗粒组成的壳层.采用氨基配体修饰后,材料的形貌无明显改变.进一步采用氮气吸附表征材料的孔结构并测定材料的比表面积和孔体积.结果表明,由于大比表面的Cu3(BTC)2的引入,复合材料Fe3O4@Cu3(BTC)2的比表面积增大为462 m2/g,孔体积为0.38 cm3/g.氨基修饰后,材料的比表面积和孔体积都有较大程度的降低,说明配体分子占据了壳层材料Cu3(BTC)2中的纳米孔道.采用苯甲醛和氰基乙酸乙酯的Knoevenagel缩合反应作为模型,考察了材料的催化活性.研究发现,Fe3O4对此反应几乎没有活性,Fe3O4@Cu3(BTC)2给出了中等的催化活性.在材料上引入氨基后,由于氨基和Cu3(BTC)2上的Lewis酸性位点的协同效应,在很大程度了提高了材料的催化活性.溶剂效应实验结果表明,反应溶剂对材料的活性和选择性具有较大影响,极性或质子性溶剂有利于反应的进行.多相催化剂的循环稳定性是其重要评价指标之一.热过滤实验结果表明,滤液中无催化活性,反应中的催化活性来源于固体材料,此催化反应为多相催化.随后考察了材料的循环稳定性.虽然氨基化Fe3O4@Cu3(BTC)2材料在溶剂DMSO中表现出最高的催化活性,但XRD和电镜表征结果表明,材料在DMSO中结构遭到破坏,因此循环过程中催化剂的活性损失严重.然后考察了氨基化材料在乙醇中的循环稳定性,发现材料在乙醇中表现出较好的循环稳定性.通过简单磁性分离进行催化剂的分离和回收,催化剂循环使用3次而没有明显的活力损失.而且,XRD和电镜表征结果显示,催化剂的结构在反应过程中没有遭到明显破坏.     

基于TiO2的绿色多相催化剂催化CO2与环氧化合物偶联反应

金属离子掺杂纳米TiO2(M-TiO2,M=Zn2+,Cu2+,Co2+,Mn2+,Ni2+)在CO2与环氧化合物的偶联反应中表现出较高的催化活性.反应以四正丁基碘化铵(TBAI)为共催化剂,在无溶剂条件下进行.考察了反应温度、反应时间和CO2压力在Zn-TiO2/TBAI体系中对反应性能的影响.作为无毒的多相催化剂,Zn-TiO2可循环使用5次,其催化活性没有明显降低.     

SBA-15分子筛负载双金属配合物的合成及其催化活性

合成了SBA-15分子筛负载的同双核金属配合物{[M2LCl3]Cl/SBA-15-NH2,M=Co,Cu,Cr,H4L=二(o-亚甲基苯亚甲基三亚乙基四胺}和异双核金属配合物{[CuEuL′](NO3)(H2O)3/SBA-15-NH2,H2L′=N,N′-二(o-羟基-m-甲酰基苯甲基)哌嗪},其结构经UV,1H NMR,IR和元素分析表征。以双核金属配合物为催化剂,过氧化氢为氧化剂,催化二苯甲烷合成二苯甲酮。考察催化剂的种类、反应时间和反应温度对该反应的影响。结果表明,在70℃反应7 h的反应条件下,[Cr2LCl3]Cl/SBA-15-NH2显示了最高的催化活性,二苯甲酮产率达58.1%。     

缺位类型磷钨酸盐催化的烯烃环氧化反应

主要合成了两种杂多磷钨酸盐环氧化催化剂,分别是由单缺位Keggin类型磷钨酸阴离子或者饱和结构的磷钨酸阴离子与十六烷基三甲基季铵盐阳离子构成,即[n-C16H33N(CH3)3]4Na3PW11O39(PW11)以及[n-C16H33N(CH3)3]3PW12O40(PW12),将其与低毒性的乙酸乙酯、30%的双氧水、烯烃构成催化环氧化反应体系,以环辛烯的环氧化反应为模型反应,着重探讨了PW11与PW12的催化性能产生明显差异的原因,并通过傅里叶变换-红外光谱,核磁共振谱以及催化剂溶解性实验给出了合理的解释.首先,在进行环辛烯的环氧化反应的动力学研究中,我们发现相同的反应条件下,PW11的催化活性明显高于PW12的催化活性,当反应进行至10min,以PW11为催化剂的反应体系,环辛烯的转化率已达到89%,而相应的采用PW12为催化剂的反应体系,环辛烯的转化率仅仅为11%.通过核磁磷谱(31PNMR)表征证明:当PW11和PW12与双氧水反应10min时PW11已降解产生大量的活性物种,而PW12的31PNMR谱并没有显示降解产物的谱峰.溶解性实验则更近一步说明,两个催化剂在双氧水的作用下均可降解形成小分子的物...     

Keggin结构过渡金属取代硼钨酸盐的电化学及电催化还原

采用循环伏安法,研究了Keggin结构过渡金属取代硼钨酸盐K7[MBW11(H2O)O39].H2O(简写为MBW11,M=Cu,Co,Ni)的电化学性质及电催化活性.结果表明,CuBW11在水溶液中表现出较为特殊的电化学性质,MBW11(M=Cu,Co,Ni)对亚硝酸根及碘酸根离子的还原反应具有较好的催化作用,取代金属对该体系的电催化活性有很大影响.     

钴系尖晶石型复合氧化物的甲烷催化燃烧性能研究

采用共沉淀法合成了钴系尖晶石型Co0.5 M0.5 Co2O4(M=Mg、Zn、Ce)复合氧化物催化剂,考察了其对甲烷催化燃烧反应的催化活性,并运用FT-IR、XRD、BET及H2-TPR等技术对催化剂进行了表征.实验结果表明,Co0.5 Ce0.5 Co2 O4催化剂有较高的催化活性,与CoO. 5Mg0.5 Co2 O4和Co0.5Zn0.5Co2 O4催化剂相比,Co0.5 Ce0.5Co2 O4催化剂有较高的晶格畸变率、较大的比表面积和孔容、较小的晶粒度、较强的氧活动性和较低的甲烷催化燃烧表观活化能.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Catalyst free,visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C₆₀, followed by SET from the amine to the triplet excited state of C₆₀. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C₆₀ radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.     

Highly efficient and stereoselective cycloaddition of nitrones to indolyl- and pyrrolylacrylates

The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (CH?O) and moderate (NH?N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities.     

Transition metal-free direct amination of benzoxazoles using formamides as nitrogen sources

A transition metal-free method for the direct amination of benzoxazoles using formamides as nitrogen sources is reported, which was mediated by an inexpensive and environmentally friendly tetrabutylammonium iodide/tert-butyl hydroperoxide system and gave the 2-aminobenzoxazole derivatives with moderate to good yields.     

l-Proline-catalyzed five-component domino reaction leading to multifunctionalized 1,2,3,4-tetrahydropyridines

Multifunctionalized 1,2,3,4-tetrahydropyridines are concisely synthesized in good yields via l-proline-catalyzed or l-proline/FeCl₃-cocatalyzed one-pot multicomponent reactions (MCRs). The MCRs involve a domino hydroamination/prins reaction/Mannich-type reaction/intramolecular dehydration-cyclization process. The molecular structure of 5baa, one of multifunctionalized 1,2,3,4-tetrahydropyridines, was confirmed by single-crystal X-ray diffraction.     

Studies of Photoionization of CF3 I by Femtosecond Time-resolved Mass Spectrometry

The multi-photon dissociative photoionization dynamics of CF3I has been studied with femtosecond two-color pump-probe time of flight mass spectra at a pump pulse of 265 nm and a probe pulse of 398 nm. The life constants of CF3I+ and its fragment ions CF3+ and I+ are obtained as (96±7), (198±130) and (167±6)fs, respectively. The multi-photon dynamics leading to these ions differ. CF3I+ corresponds to a (1+2′) transition with one-photon pump excitation to the A band of CF3I. CF3+ are mainly formed by a tow-photon probe excitation to the CF3+ with subsequent dissociation of parent ions. I+ are produced in (2+2′) combined with (1+1′+2′) process. The results provide information on the multi-photon pathways involved.