Novel catalysts for syndiospecific polymerization of styrene

The current development of the metallocene-based catalysts for syndiotactic polystyrene (SPS) has been reviewed. SPS is a new semi-crystalline engineering thermoplastic with a crystalline melting point of 270°C. Because of its crystalline nature, SPS has high heat resistance, excellent chemical resistance and waterysteam resistance. In this review, some mechanistic models for polymerization and stereoregulation, as well as the factors which affect the activity and stereospecificity of the catalysts, are discussed.     

Syntheses and properties of syndiotactic polystyrene

Syndiotactic polystyrene (SPS) is a new crystalline engineering thermoplastic. With a melting point of 270 °C and its crystalline nature, SPS has high heat resistance, excellent chemical resistance and water/steam resistance. Since SPS has excellent dielectric properties, it is useful as a capacitor insulation material. The rate of crystallization is very fast in comparison with isotactic polystyrene (IPS), thus, SPS can be used in a number of forming operations, including injection molding, extrusion and thermoforming. A system composed of a homogeneous titanium compound and methylaluminoxane (MAO) is an effective catalyst for syndiospecific polymerization of styrene. On the other hand heterogeneous titanium compounds containing halogen make a mixture of isotactic and syndiotactic components. The amount of syndiotactic polystyrene obtained is dependent on the mole ratio of Al to Ti. The result of ESR measurement suggests the Ti³⁺ species are important as a highly active site for producing syndiotactic polystyrene. A comparison of the stereoregularities of polypropylene and polystyrene formed by various metallocene catalysts is studied. The (C₆H₆)₂C(η₅-C₅H₄)(η₅-C₉H₆)TiCl₂/MAO system gives a homogeneous catalyst for the polymerization of propylene giving isotactic rich polypropylene and of styrene to give syndiotactic polystyrene.     

Nonisothermal crystallization behavior of SPS/APS blends

The nonisothermal crystallization behavior of syndiotactic polystyrene (SPS)/atactic polystyrene (APS) blends was studied with differential scanning calorimetry to investigate the effects of APS on the crystallization behavior of SPS. Polarized optical microscopy and wide‐angle X‐ray diffractometry were also used to observe the morphology of the SPS crystalline structure. From a cyclic heating/cooling temperature program, we obtained found that APS retarded the crystallization (and recrystallization) of SPS and made the crystal less perfect, but the ultimate crystallinity of SPS did not change with the addition of APS. We also observed that APS was disposed in the interfibrillar region of SPS spherulites and did not change the crystalline form of SPS. This result will be helpful for improving SPS applications through blending with rubber‐toughened APS. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3001–3008, 2000     

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.     

Hydrogen production by methanol steam reforming on a cordierite monolith reactor coated with Cu–Ni/LaZnAlO<Subscript>4</Subscript> and Cu–Ni/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The performance of Cu–Ni/LaZnAlO₄ and Cu–Ni/γ-Al₂O₃ catalysts in the methanol reforming process in a monolith reactor in the temperature range of 200–350 °C, feed flow rate of WHSV = 20.8 h^?1 and atmospheric pressure has been investigated. In order to perform a more thorough investigation, surface area, morphology and crystalline structure of the synthetic catalysts have been studied using BET, FE-SEM, TPR, FT-IR, TEM, TGA and XRD analyses. The results have shown that Cu–Ni/LaZnAlO₄ catalyst synthesized by combustion reaction method under ultrasound irradiation has a very high efficiency and catalytic activity, low reduction temperature, high mechanical resistance and large pore sizes. The latter causes a higher percentage of active metal impregnation and better distribution on the support, greater resistance against sintering and maintenance of catalyst inertness at temperatures over 1000 °C, in comparison with conventional catalysts such as Cu–Ni/γ-Al₂O₃. This make its substitution for currently used catalysts affordable.     

TiO2晶型对Au/TiO2上光催化分解臭氧的影响

以不同晶型TiO2为载体,采用沉积-沉淀法制备了Au/TiO2光催化剂,并用紫外-可见漫反射光谱、X射线光电子能谱(XPS)和表面光电压谱(SPS)等手段进行了催化剂表征,详细考察了Ti O2晶型对Au/TiO2光催化分解臭氧活性的影响.结果表明,光催化分解臭氧的活性顺序为Au/P25>Au/Anatase>Au/Rutile,这与不同的单一Ti O2对光催化臭氧分解的活性顺序是一致的.但在TiO2上沉积金后,其对光催化臭氧的分解活性有了显著的提高.由催化剂的Au4fXPS分析发现,不同晶型Ti O2上的电荷向金簇迁移的能力有明显差异,加之载体本身对光催化臭氧分解活性不同,两者协同作用导致负载金催化剂光催化分解臭氧活性的不同.SPS信号强度与催化剂光催化活性有很好的对应关系,SPS信号越强,光生电子和空穴分离效率越高,光催化活性越好.     

引入离子基团改善聚苯乙烯和热致液晶聚合物的相容性 Ⅰ热性能和形态

ＤＳＣ和ＳＥＭ研究结果表明聚苯乙烯（ＰＳ）与一种热致液晶聚合物（ＬＣＰ）（ＰＨＢ／ＰＥＴ（６０／４０）共聚酯）完全不相容．共混体系具有与组分无关的Ｔｇ，并且表现出明显的两相结构．将ＰＳ进行化学改性（引入磺酸基团）制备成磺化聚苯乙烯（ＳＰＳ），随中和盐离子的变化有：酸式、Ｌｉ、Ｎａ、Ｚｎ和Ｍｎ盐五种形式．用ＤＳＣ和ＳＥＭ对ＬＣＰ与ＳＰＳ共混物的热性能和形态进行了分析和表征．共混体系有一个与组成相关，且明显低于纯ＳＰＳ的Ｔｇ．这表明了ＰＳ与ＬＣＰ的相容性因为磺酸基团的引入而得到了改善．同时用Ｆｏｘ方程计算了ＬＣＰ的Ｔｇ．当ＳＰＳ含量较低时（不大于５０％）在各个共混体系中，所估算的ＬＣＰ的Ｔｇ相互吻合．表明共混体系满足Ｆｏｘ方程的前提条件，即ＬＣＰ与ＳＰＳ形成相容体系．当ＳＰＳ含量较低时（２５％），ＬＣＰ／ＳＰＳ的共混物为较均一体系，断面光滑；而ＳＰＳ含量较高时，在脆断面可以观察到纳米级的颗粒．电子能谱分析证明了这些颗粒是ＳＰＳ负离子的聚集体．     

Electrochemical properties of carbon nanotube-supported metallic catalysts prepared by changing a sweep- or step-applied potential

The electrochemical deposition of Pt nanoparticles on carbon nanotube (CNTs) supports and their catalytic activities for an electro-oxidation were investigated. Pt catalysts of 4–12 nm average crystalline size were grown on supports by changing applied potential methods such as sweep-potential or step-potential. Electroplating of 24-min time by a step-applied potential was enough to obtain small crystalline-size 4.6-nm particles, resulting in good electrochemical activity. The catalysts’ loading contents could be controlled by increasing the deposition time. The crystalline sizes and structures of the Pt/support catalysts were analyzed using X-ray diffraction (XRD). The electrochemical properties of the Pt/support catalysts were studied according to their characteristic current–potential curves in a methanol solution. As a result, the electrochemical activity was increased by enlarging the plating time. The activity reached the maximum at 24 min and then decreased. The enhanced electroactivity for catalysts by step-potential methods could be explained by the changes of the crystalline size and crystalline structures of the catalysts.     

Soluble,Antibaterial, and Anticorrosion Studies of Sulfonated Polystyrene/Polyaniline/Silver Nanocomposites Prepared with the Sulfonated Polystyrene Template

In this work, multifunctional sulfonated polystyrene/polyaniline/silver (SPS /PANI /Ag) nanocomposites are prepared through using sulfonated polystyrene (SPS ) spheres as templates and utilizing polyvinylpyrrolidone (PVP ) as reducing agent and stabilizing agent. Our method is an environmentally friendly method because no toxic reagents are added during the preparation process. Fourier transform infrared spectrum (FTIR ), field emission scanning electron microscopy (FESEM ), and energy disperse spectroscopy (EDX ) results confirmed the formation of PS spheres, SPS spheres, SPS /PANI nanocomposites, and SPS /PANI /Ag nanocomposites. Powder X‐ray diffraction (XRD ) patterns indicate that the obtained Ag nanoparticles are crystalline. Solubilities measurements show that SPS /PANI /Ag nanocomposites have improved solubilities when compared to pure PANI in common organic solvents and deionized water. Antibacterial studies show that SPS /PANI /Ag nanocomposites can greatly inhibit the growth of Escherichia coli and Staphylococcus aureus . Anticorrosion studies show that the incorporation of SPS /PANI /Ag nanocomposites in waterborne alkyd resin can greatly promote the anticorrosive efficiency of waterborne alkyd resin.     

Synthesis of Nano-catalysts by Induction Suspension Plasma Technology (SPS) for Fischer–Tropsch Reaction

Nanometric catalysts were synthesized through induction suspension plasma technology (SPS) for application in the Fischer–Tropsch synthesis (FTS). Carbon-supported single metal catalysts (Co/C, Fe/C), bimetallic formulations (Co–Fe/C), and ternary (Co–Fe–Mo and Co–Fe–Ni) systems have been considered in this work. SPS has been selected because it simultaneously allows for: (1) atomizing and generating metallic nanoparticles; (2) creating particularly Fe carbides, which are important in Fe-based FTS reaction mechanism; (3) in situ production of the nanometric graphitic-carbon matrix; and (4) saving time in catalyst synthesis, limiting sample preparation steps and eliminating post synthesis treatment before use. Porosity measurements by the Brunauer–Emmett–Teller method indicate that the samples are essentially non-porous. The synthesized catalysts characterized by X-ray Diffraction analysis show the presence of both metallic and carbidic species. The graphitic-carbon matrix has substantial structural defects that make it partly amorphous. Scanning Electron Microscopy analysis coupled with Energy Dispersive X-ray Spectroscopy mapping shows uniform dispersion of the metal moieties in the carbon support. Analysis by Transmission Electron Microscopy imaging displays metal nanoparticles with mean particle size within the 9–15 nm range enveloped in the carbon matrix.     

急冷非晶态镍合金催化剂的研究开发和工业应用

Raney Ni催化剂是石油化学工业用量最大的催化剂之一,通过急冷技术将其晶态结构转变为非晶态结构,能够提高加氢活性.但非晶态合金热稳定性差、比表面积小限制了这类催化材料的工业应用.通过加入少量稀土元素,使非晶态 Ni 晶化温度提高200 K以上; 通过加入Al再碱抽Al,使非晶态Ni比表面积增加100倍以上; 通过加入功能助剂调节非晶态Ni的加氢选择性、增加抗酸碱腐蚀性和磁性,从而形成了系列非晶态Ni加氢催化剂 (商品名为 SRNA).其中,SRNA-1 用于药物中间体加氢; SRNA-2用于葡萄糖加氢制山梨醇; SRNA-3用于汽、柴油吸附脱硫; SRNA-4用于己内酰胺加氢精制; SRNA-5 用于苯甲酸加氢中替代Pd/C催化剂,使后者的用量减少了50%.     

化学配比调制表面带弯对表面光电压谱的影响

表面光电压技术发展于六十年代初期，Goodman［‘］曾用来测量半导体中少数载流子的扩散长度．在少数载流于扩散长度的计算公式中，无光照射时的表面带弯K。是极重要的参数，改变K。以检验公式的物理意义尤为重要．但早期的研究工作不能显著地改变Vso值．近年来虽出现了一些调制表面带弯的物理手段，如在涮量电极和样品间加一层铁电晶体【到或花样品两侧施加电场等【司，但其效果均不十分理想．表面光电压技术与化学的联系日益密切，王德军等P问到曾尝试将其应用到化学领域中以研究界面电行转移与固体表面酸度．本文则考虑应用化学方法来…     

Unusual Assembly and Conversion of Graphene Quantum Dots into Crystalline Graphite Nanocapsules

The development of a facile strategy for conversion of graphene quantum dots (GQDs) into crystalline graphite is of great practical significance and still remains challenging. Herein, rationally assembled crystalline‐intercrossed graphite nanocapsules (CI‐GNCs) have been realized by a one‐step electrochemically induced strategy with the assistance of a soft template, in which the GQDs act as the initial building blocks. The as‐prepared CI‐GNCs exhibit highly crystalline graphitic nanostructures. Moreover, they possess promising electrocatalytic activity for the oxygen reaction reduction (ORR) in alkaline medium. This simple fabrication technology presents a great advance for synthesizing CI‐GNCs composite catalysts, which have potential as new metal‐free catalysts for efficient ORR applications.     

Fe/Zn双金属氰化物催化剂催化环氧丙烷聚合的活性结构研究

以氯化锌、铁氰化钾（含有整合剂）的水溶液为原料，合成了铁锌双金属氰化物（DMC）催化剂。为获得高活性的DMC催化剂，需将叔丁醇 、多元醇螯合剂螯合至其结构中，用XRD、XPS等分析手段，对铁锌DMC催化剂的结构与活性进行分析表征。实验发现，DMC催化剂的晶体结构与螯合剂密切相关，螯合剂能显著降低DMC催化剂的结晶程度，从而提高DMC催化剂的活性。同时，氯化锌过量也有利于DMC催化剂活性的提高。并表征了相关DMC催化剂的活性中心。     

Cyclodehydration of 1,4-butanediol catalyzed by metal(IV) phosphates

Metal(IV) phosphates of tin, zirconium and titanium in different morphological forms, viz. amorphous, calcined and crystalline, have been used as catalysts for selective cyclodehydration of 1,4-butanediol to tetrahydrofuran. A comparative study of the three catalysts for the above reaction has been carried out to understand the effect of their composition and morphology on the catalytic activity.     

GAS SORPTION,DIFFUSION AND PERMEATION OF ORDERED POLYMERIC MEMBRANES

He, CO_2, O_2, N_2, CH_4, C_3H_8, and t-C_4H_(10) gas permeability coefficients and diffusion coefficients of poly(4-methylpentene-1) (PMP) with various degrees of crystallization were plotted against the degree of crystallization. The plotdemonstrated a linear relationship. The gas permeability coefficient and diffusion coefficient of pure amorphous and purecrystalline PMPs were evaluated by a linear extrapolation to zero and 100% crystallinity, respectively. The relationshipbetween the diffusion coefficient of crystalline parts of PMP and the kinetic diameter of penetrant gases was discussed.Syndiotactic polystyrene (SPS) could exist as δ form crystals complexed with organic solvents such as benzene, toluene,xylene, and ethylbenzene. The mesophase of SPS is prepared by annealing the δ form of crystalline complexes at a certaintemperature for 1 h. The desorption of solvent during annealing almost does not result in changes of both the conformation ofbackbone chains and the crystal lattice. We could prepare the mesophase containing molecular cavities with the size andshape of the organic solvent molecules. The mesophase could sorb the same solvent after the manner of Langmuir sorption atlow vapor pressure range while this would not be the case for solvents of different size and shape. This suggests a molecularrecognition of organic solvent, and mesophase SPS might be useful for separation membrane and adsorptive material.     

Miscibility evaluation of SPS/APS blend investigated from crystallization dynamics

The miscibility of crystalline syndiotactic polystyrene (SPS)/non-crystalline atactic polystyrene (APS) blend was estimated by the crystallization dynamics method, which evaluated the nucleation rate, the crystal growth rate and the surface free energy parameter. The melting temperature depression suggested that SPS/APS blends were the miscible system but not in molecular level. The relationship between the blend content and the chemical potential difference evaluated at a constant crystal growth rate showed a good linear relationship. These facts suggested that SPS/APS blends contained the concentration fluctuation with the size between few nm to less than 80 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

预处理条件对用于CO_2加氢的超细CuO－ZnO－SiO_2催化剂性能的影响

采用ＸＲＤ、ＢＥＴ、ＴＰＲ手段，研究了焙烧和还原温度对超细ＣｕＯ－ＺｎＯ－ＳｉＯ２催化剂的性质及其ＣＯ２加氢反应催化活性的影响．胶体在５７３－７７３Ｋ范围内焙烧生成ＣｕＯ、Ｃｕ２Ｏ、ＺｎＯ晶相，随着焙烧温度继续升高，ＣｕＯ和ＺｎＯ晶粒逐渐变大，但催化剂的比表面积和孔容变化很小．在９７３Ｋ焙烧后出现Ｚｎ２ＳｉＯ４晶相，使催化剂比表积和孔容变小，导致催化剂活性降低．焙烧温度对催化剂活性的影响大于对ＣＯ２加氢产物分布的影响．在５４８－６４８Ｋ范围内，催化剂还原温度对其催化活性影响不大．７０３Ｋ高温还原后，可能由于Ｃｕ０晶粒的出现，使得催化剂的活性下降．ＴＰＲ研究结果进一步表明，焙烧温度影响ＣｕＯ同ＺｎＯ、ＳｉＯ２之间的相互作用和催化剂的还原行为．     

表面活性剂对完全液相法制Cu-Zn-Al浆状催化剂结构和性能的影响

采用完全液相法制备了Cu-Zn-Al双功能浆状催化剂, 利用不同类型表面活性剂对其进行了修饰和改性. 通过N2气吸附、XRD和XPS等方法考察了表面活性剂类型对催化剂织构、物相以及表面性质的影响, 采用浆态床反应装置对其合成气一步法制备二甲醚的催化活性进行了评价, 讨论了催化剂结构与性能的关系. 结果表明, 表面活性剂主要是通过与活性金属的作用调节催化剂的表面性质、孔结构、相结构以及晶粒大小, 进而影响催化剂的催化活性; 非离子表面活性剂总体上对催化剂的性能有促进作用, 阳离子表面活性剂和阴离子表面活性剂对催化剂性能存在不利影响; 表面活性剂与活性金属作用的强弱是影响性能的关键.     

α-Bi~2Mo~3O~1~2/MoO~3催化剂的表面光电压谱研究

合成了系列催化剂Bi~xPMo~1~2O~y(x=2-9, y=43-64), 高温焙烧后该系列催化剂的基本组成为白钨矿型的α-Bi~2Mo~3O~1~2/MoO~3。研究其表面光电压谱发现, 随着Bi/P比的增高, 相应的光电压响应呈现规律性变化。在该系列催化剂上的丙烷选择氧化实验结果表明, 铋含量增加, 催化剂中作为碱性位的阳离子缺陷的浓度随着白钨矿结构中阳离子空位的有序化而下降, 反映在光电压响应中对应着P~1带强度的减弱和P~2带的负移, 而与之对应的催化活性迅速下降。