焙烧及还原温度对对硝基苯酚加氢合成对氨基苯酚Ni/TiO2催化剂性能的影响

采用等体积浸渍法制备了Ni/TiO2催化剂,考察了焙烧和还原温度对其结构及催化对硝基苯酚加氢合成对氨基苯酚反应性能的影响,利用X射线衍射、程序升温还原及H2化学吸附等方法对催化剂进行了表征.结果表明,923 K以下焙烧制备的催化剂中镍物种主要以与载体相互作用不同的NiO形式存在,随着焙烧温度的升高,催化剂中NiO与TiO2间的相互作用增强.经723 K还原后,随焙烧温度升高,催化剂的H2化学吸附量减小,而923 K焙烧的催化剂具有较佳的加氢反应性能,这与金属镍和TiOx(x<2)的协同作用有关.对于923 K焙烧的催化剂,当还原温度较低时,NiO还原不完全,金属镍与TiOx的相互作用较弱,催化剂活性较低;当还原温度过高时,镍晶粒发生烧结,并且催化剂的镍活性表面因镍与TiOx的相互作用增强而减小,从而导致催化剂活性降低,适宜的还原温度为673 K.当Ni/TiO2催化剂具有适宜的镍活性表面及适宜的金属镍与TiOx相互作用时,金属镍与TiOx的协同对-NO2的加氢活化最为有利.     

镍负载量对邻氯硝基苯加氢制邻氯苯胺Ni/TiO2催化剂性能的影响

 用等体积浸渍法制备了一系列不同镍负载量的负载型Ni/TiO2催化剂,并将其应用于邻氯硝基苯加氢制邻氯苯胺的反应. 采用N2吸附、 X射线衍射、程序升温还原、透射电镜、 H2化学吸附及间歇加压釜式反应器活性评价等方法,考察了镍负载量对Ni/TiO2催化剂的物化性质及邻氯硝基苯加氢反应性能的影响. 结果表明,随着镍负载量的增加, Ni/TiO2催化剂上邻氯硝基苯的转化率逐渐提高; 当镍负载量超过30%时,催化剂的活性和选择性不再明显变化. 当催化剂中镍负载量高于20%时,在温度343 K、 氢压1.0 MPa和催化剂/邻氯硝基苯质量比1/10的条件下反应210 min后,邻氯硝基苯的转化率和邻氯苯胺的选择性均高于99%, 催化剂具有良好的应用前景. 分析表明,影响Ni/TiO2催化剂性能的主要因素为催化剂表面镍晶粒的活性表面积以及载体TiO2与金属镍之间的强相互作用.     

镍基催化剂上糠醛选择性加氢合成糠醇

采用浸渍法制备了一系列负载的Ni催化剂,用于糠醛选择性加氢反应.用XRD、TPR等手段对Ni/γ-Al2O3样品进行了表征.结果表明,Ni负载量在5~|15%范围内,高度分散于载体γ-Al2O3表面,Ni负载量进一步提高到20%,则在载体表面聚集成为微晶.在10%Ni/γ-Al2O3样品上提高焙烧温度有利于Ni的前驱体分解且高度分散于载体表面.Ni2 与γ-Al2O3存在较强的相互作用,但这种相互作用随着Ni负载量的增加而逐渐减弱,随着焙烧温度的增加而逐渐增强.与其他载体负载的Ni催化剂相比,Ni/γ-Al2O3由于其大的表面和适当的表面结构,在糠醛加氢反应中表现出一定的活性和较高的选择性,且随着Ni负载量的增加,活性逐渐增强,但选择性有所下降.另外催化剂的焙烧温度、还原温度,反应温度和溶剂对该反应均有较大影响,采用极性有机溶剂,适宜的焙烧和还原温度有利于催化剂活性和选择性的提高.     

镍基催化剂上苯酐选择性加氢合成苯酞

分别以SiO2,TiO2,γ-Al2O3,TiO2-SiO2和TiO2-Al2O3为载体,以硝酸镍为镍源,采用等体积浸渍法制备了一系列镍基催化剂,并将其用于苯酐选择性加氢合成苯酞反应.结果表明,以TiO2-SiO2为载体制备的镍催化剂上Ni0活性组分分散度较高,催化剂表现出较高的活性和苯酞选择性.在此基础上,采用溶胶-凝胶法制备出了一系列Ni/TiO2-SiO2催化剂,考察了催化剂制备中各因素(包括溶剂、焙烧温度、还原温度和镍前驱体类型等)对其催化苯酐加氢反应性能的影响.结果表明,将镍前驱体溶于不同溶剂制备的催化剂性能差异很大,其中以水为溶剂制备的催化剂活性较高,且性能优于等体积浸渍法制备的相应催化剂.焙烧温度和还原温度过高会导致活性组分镍晶粒度变大,致使催化剂活性明显降低.镍源对Ni/TiO2-SiO2催化剂的性能影响较大,以硫酸镍为镍源制备的催化剂几乎无活性,而以氯化镍和硝酸镍为镍源制备的催化剂表现出较高的催化活性和选择性,其中以氯化镍制备的催化剂性能略高于硝酸镍,苯酐转化率为100%,苯酞选择性为88.5%.     

磷化镍/介孔TiO_2催化剂的制备及其催化加氢脱硫性能

以介孔TiO2(m-TiO2)为载体,采用程序升温还原法制备了Ni2P/m-TiO2催化剂,考察了不同起始Ni/P摩尔比及活性组分负载量对该催化剂结构及其催化加氢脱硫(HDS)性能的影响.结果表明,当Ni/P摩尔比为1.25时,活性组分以Ni2P为主,催化剂的最佳Ni负载量为10%.采用X射线衍射、低温N2吸附-脱附、场发射扫描电镜和程序升温还原等技术表征了m-TiO2及其它不同载体负载的Ni2P催化剂.结果表明,高结晶度m-TiO2载体使Ni和P物种的还原温度大幅度降低,在450～600oC还原制得的Ni2P/m-TiO2催化剂的结构参数基本一致,比表面积均为90m2/g左右,具有很高的热稳定性和对二苯并噻吩的HDS催化性能.在相同的反应条件下,m-TiO2负载的Ni2P催化剂HDS性能最好,各载体负载的Ni2P催化剂活性大小顺序为Ni2P/m-TiO2Ni2P/SiO2Ni2P/P25.     

介孔TiO_2晶须担载Au的热稳定性(英文)

以二钛酸钾晶须为前驱体,通过固相烧结工艺制备了介孔TiO2晶须,然后使用沉积沉淀法将Au纳米颗粒担载于其上,并采用低温N2吸附-脱附、X射线衍射及透射电镜等技术对催化剂的形貌和结构进行了表征,以NaBH4还原对硝基苯酚(PNP)为探针反应,评价了催化剂的活性及稳定性.结果表明,500°C热处理前后,介孔TiO2负载的Au纳米颗粒的平均粒径变化不大,且催化PNP还原活性得到了很好的保持.这主要与介孔TiO2晶须独特的双晶构型及介孔结构有关.     

介孔TiO2晶须担载Au的热稳定性（英文）

以二钛酸钾晶须为前驱体,通过固相烧结工艺制备了介孔TiO2晶须,然后使用沉积沉淀法将Au纳米颗粒担载于其上,并采用低温N2吸附-脱附、X射线衍射及透射电镜等技术对催化剂的形貌和结构进行了表征,以NaBH4还原对硝基苯酚(PNP)为探针反应,评价了催化剂的活性及稳定性.结果表明,500°C热处理前后,介孔TiO2负载的Au纳米颗粒的平均粒径变化不大,且催化PNP还原活性得到了很好的保持.这主要与介孔TiO2晶须独特的双晶构型及介孔结构有关.     

TiO2-Al2O3复合氧化物载体焙烧温度对Au-Pd催化剂加氢脱硫性能的影响

 采用溶胶-凝胶法制备了介孔TiO2-Al2O3复合氧化物载体,考察了载体的焙烧温度对负载型Au-Pd双金属催化剂加氢脱硫性能的影响,并采用X射线衍射、吸附吡啶的程序升温脱附、程序升温还原、红外光谱和N2物理吸附等技术对载体及催化剂进行了表征. 结果表明,不同温度焙烧的TiO2-Al2O3复合载体都具有介孔结构,其中773 K焙烧制得的TiO2-Al2O3复合载体的比表面积和孔容较大, B酸中心较多,以其为载体的Au-Pd 催化剂具有较好的加氢脱硫活性. 表征结果表明, 773 K焙烧制得的Au-Pd/TiO2-Al2O3催化剂中Au-Pd活性组分与载体的相互作用较强,催化剂上形成的AuxPdy合金的晶粒较小且数量较多,催化剂的酸量和活性组分的分散度较大,并且其上进行的加氢脱硫反应的活化能较低,这些因素均有利于催化剂活性的提高.     

Ni2P/TiO2的制备及其对苯加氢反应的催化性能

采用程序升温还原方法制备了TiO2负载的晶态Ni2P催化剂。用X射线衍射（XRD）及低温N2吸附（BET）等技术对样品的物相、比表面积等性质进行了表征。以苯气相加氢为模型反应考察了Ni2P/TiO2催化剂加氢性能，并对Ni2P负载量、前驱体中P的质量分数对催化剂的物相及性能的影响进行了研究。实验结果表明， TiO2负载的晶态磷化镍催化剂上，Ni2P是主要物相。Ni2P/TiO2催化剂对苯加氢反应具有较高的活性、选择性以及良好的稳定性能。Ni2P/TiO2制备对催化剂的性能有影响。Ni2P负载量增加，催化剂的活性先升高后降低，Ni2P负载量为12%时催化剂活性较高。催化剂前驱体中P的质量分数越高，制备出的催化剂对苯加氢反应的稳定性越好，但随前驱体中P的质量分数增加，催化反应的活性先升高，后降低。与Ni2P/SiO2比较，Ni2P/TiO2催化剂具有较高的活性和稳定性。     

镍负载量对乙醇水蒸气重整制氢催化性能和催化剂的影响

采用稳态实验对镍负载量对Ni/MgO催化剂在乙醇水蒸气重整反应的影响进行了研究。结果表明，在101.3kPa下，镍负载量越高，催化剂的活性越高。对于催化剂的选择性，存在一个最佳镍负载量为10%Ni/MgO。按选择性从大到小排序，不同镍负载量的催化剂为：10Ni/MgO>15Ni/MgO>12.5Ni/MgO>7.5Ni/MgO≈5Ni/MgO。热分析表明，焙烧过程中不同镍负载量的催化剂镍前体与载体前体之间发生的相互作用不同。XRD和TPR 表征结果显示，催化剂的晶体结构和还原特性也与催化剂上镍的负载量有关。焙烧过程中样品10Ni/MgO上镍前体与载体前体发生了两种相互作用, 并且其氧化态与其他催化剂相比具有特殊的结构和还原性。说明催化剂的选择性不仅受活性相Ni的影响而且受Ni活性相周围环境的影响。     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

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.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

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.