Gasoline-range hydrocarbon synthesis over cobalt-based Fischer-Tropsch catalysts supported onSiO2/HZSM-5

Two types of SiO2 with different mesopore size and HZSM-5 zeolite were used to prepare hybrid supported cobalt-based catalysts. The textual and structural properties of the catalysts were studied using N-2 physisorption, X-ray diffraction (XRD), and H-2 temperature-programmed reduction (TPR) techniques. Fischer-Tropsch synthesis (FTS) performances of the catalysts were carried out in a fixed-bed reactor. The combination effects of the meso- and micropores of the supports as well as the interaction between supports and cobalt particles on FTS activity are discussed. The results indicate that the catalyst supported on the tailor-made SiO2 and HZSM-5 hybrid maintained both meso- and micropore pores during the preparation process without HZSM-5 particles agglomerating. The mesopores provided quick mass transfer channels, while the micropores contributed to high metal dispersion and accelerated hydrocracking/hydroisomerization reaction rate. High CO conversion of 83.9% and selectivity to gasoline-range hydrocarbons (C-5-C-12) of 55%, including more than 10% isoparaffins, were achieved simultaneously on this type of catalyst.

磷酸盐催化剂上气相选择氧化的研究

有机化合物的选择氧化反应，特别是烃类的选择氧化，在石油化工中占有极其重要的地位。由于目标产物通常具有较高的活泼性，所以很难在高转化率条件下获得高选择性的氧化产物。因此对于催化研究者来说，如何控制深度氧化，提高目的产物的选择性始终是选择氧化，特别是烃类选择氧化研究中最具挑战性的技术难题。磷酸盐具有高度热稳定性，制备条件简单方便，原料价格低廉，而且其催化活性位区域易于与大分子反应等优点。其中磷酸钒、磷酸铁及其它过渡金属磷酸盐既具有氧化一还原性又有良好的表面酸性，在烃类等选择氧化反应中已表现出良好的催化性能，因而，研究磷酸钒、磷酸铁等磷酸盐催化剂在选择氧化中的催化作用具有重要的学术意义和应用前景。本论文主要在几个方面的工作研究了磷酸盐催化剂在气相选择氧化中的催化作用。探讨了过渡金属对层状磷酸钒的修饰，并以它们为催化剂前驱体，以甲苯气相选择氧化为探针反应，研究了过渡金属修饰对磷酸钒催化性能的影响。利用简单的方法直接合成了一个新的乙酞丙酮铜插层的层状磷酸钒，并用XRD、FTIR、ICP-MS、TGA和HRTEM对其进行了表征，确定合成的化合物分子式为：［Cu（acac）」0.5?VOH0.5PO4?0.5H2O。利用十二烷基胺通过简单直接的方法合成了中孔层状磷酸钒，并用XRD、FTIR?ICP一MS和TGA对其进行了表征，确定所合成的化合物主体磷酸钒为VOHPO4，十二烷基胺在VOHPo4的结构中通过与主体HPo4中的一H形成RNH3＋和与VoHPO4层内的V＝O形成氢键（V=O…H2NR）构成双层排列结构。利用烷基胺形成中孔层状结构的方法引入过渡金属钻和镍进入磷酸钒。以合成铜、钻和镍修饰的磷酸钒为前驱体，经焙烧后得到催化剂，甲苯气相选择氧化反应的结果表明，铜、钻和镍的修饰促进了磷酸钒的催化性能，提高了苯甲醛的选择性。发现了控制气相选择氧化产物选择性的新途径。以磷酸钒为催化剂，在环己烷、环己烯气相氧化反应中，通过在原料中加入醋酸改变了反应产物的分布，抑制了中间产物的深度氧化，可获得高选择性的目标产物。在反应温度450℃，当醋酸与环己烷、环己烯摩尔比为12.9：1和12.1：1时，分别获得了100％选择性的不稳定中间产物环己烯和1，3-环己二烯。研究了不同磷酸钒相对环己烷氧化脱氢反应的催化性能，表明在醋酸体存在条件下，催化性能顺序为：QI一OPO4＞aII-VOPO4＞pVOPO4＞（VO）2P2O7。发现催化剂表面酸性强度不同和醋酸之间的相互作用力也不同，表面酸性越强；抗醋酸能力越强，活性中心与醋酸作用越弱，未与醋酸相互作用的活性中心数目越多，因此催化活性相对越高。同时，研究了不同载体对环己烯氧化脱氢的影响，比表面积越大，有利于提高催化剂的活性，但不利于获得高选择性的1，3-环己二烯；碱性载体有利于1，3-环己二烯的生成，但易于与醋酸反应而使催化剂失活。提出了醋酸在环己烷和环己烯氧化脱氢中作用机制：醋酸优于环己烷（烯）吸附在VPO催化剂表面活性位，这将导致在反应物吸附活性位周围几乎没有相邻的活性中心。即加入醋酸使催化剂表面形成了孤立的活性位，有利于中间物种不被继续氧化。利用上面的方法，以磷酸铁和磷酸钒为催化剂，实现了对甲酚气相选择氧化，获得100％选择性的对轻基苯甲醇、对经基苯甲醛和／或对轻基苯甲酸的混合物。与磷酸钒相比较，磷酸铁催化剂更温和，得到主要产物为对轻基苯甲醇和对经基苯甲醛；而磷酸钒催化剂更易产生深度氧化的产物对经基苯甲酸。这主要是由于他们表面酸性和氧化一还原性能的不同引起的。以磷酸铁、磷酸铜和磷酸秘为催化剂，探索了苯甲醇的气相选择氧化。研究了不同Fe（II）／Fe（III）比磷酸铁的催化活性。对于磷酸铁、磷酸铜和磷酸秘催化剂，最佳苯甲醛收率分别是在反应温度320℃、275℃和325℃，苯甲醛选择性分别为92.3％、97.1％、92.6％，相应苯甲醇的转化率为96.5％、60.9％和98.6％。

Visible vertical cavity surface emitting laser

We have designed and fabricated the visible vertical-cavity surface-emitting lasers (VCSEL's) by using metalorganic vapor phase epitaxy (MOVPE). We use the 8 lambda optical cavities with 3 quantum wells in AlGaInP/AlGaAs red VCSEL's to reduce the drift leakage current and enhance the model gain in AlGaInP active region. The structure has a p-type stack with 36 DBR pairs on the top and an n-type with 55-1/2 pairs on the bottom. Using micro-area reflectance spectrum, we try to get a better concordance between the center wavelength of DBR and the emitting wavelength of the active region. We used a component graded layer of 0.05 lambda thick (x = 0.5 similar to 0.9) at the p-type DBR AlGaAs/AlAs interface to reduce the resistance of p-type DBR. We use selective oxidation to define the current injection path. Because the oxidation rate of a thick layer is faster than a thinner one, we grown a thick AlAs layer close to the active region. In this way, we got a smaller active region for efficient confinement of injected carriers (the aperture area is 3 x 3 mu m) to reduce the threshold and, at the same time, a bigger conductive area in the DBR layers to reduce the resistance. We employ Zn doping on the p-side of the junction to improve hole injection and control the Zn dopant diffusion to get proper p-i-n junction. At room temperature, pulse operation of the laser has been achieved with the low threshold current of 0.8mA; the wavelength is about 670nm.

Facile synthesis of ginsenoside Ro

Two concise synthetic routes, being different in the glycosylation sequence, toward ginsenoside Ro (1) are developed. These syntheses feature the elaboration of the glucuronide residue at a later stage via the TEMPO-mediated selective oxidation and the installation of AZMB as a benzoylic neighboring participating group capable of being selectively removed afterward.

Novel cobalt-free oxygen permeable membrane

A series of cobalt-free and low cost perovskite oxygen permeable membranes based on BaCexFe1-xO3-delta (BCF) oxides was successfully synthesized and the membrane showed both high oxygen permeability and high stability under reductive atmosphere, which will be most suitable for constructing a membrane reactor for selective oxidation of light hydrocarbons to syngas or high value corresponding oxygenates.

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Isolated transition metal ions/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g., TS-1, Fe-ZSM-5, and V-MCM-41) or on the surface of oxides (e.g., MoO3/Al2O3 and TiO2/SiO2) were successfully identified by UV resonance Raman spectroscopy. The charge transfer transitions between the transition metal ions and the oxygen anions are excited by a UV laser and consequently the UV resonance Raman effect greatly enhances the Raman signals of the isolated transition metal ions. The local coordination of these ions in the rigid framework of molecular sieves or in the relatively flexible structure on the surface can also be differentiated by the shifts of the resonance Raman bands. The relative concentration of the isolated transition metal ion/oxides could be estimated by the intensity ratio of Raman bands. This study demonstrates that the UV resonance Raman spectroscopy is a general technique that can be widely applied to the in-situ characterization of catalyst synthesis and catalytic reactions. (C) 2003 Elsevier Science (USA). All rights reserved.

Investigation of Chemical Bond Characteristics, Thermal Expansion Coefficients and Bulk Moduli of alpha-R2MoO6 and R2Mo2O7 (R = rare earths) by Using a Dielectric Chemical Bond Method

Theoretical researches are performed on the alpha-R2MoO6 (R = Y, Gd, Tb Dy, Ho, Er, Tm and Yb) and pyrochlore-type R2Mo2O7 (R = Y, Nd, Sm, Gd, Tb and Dy) rare earth molybdates by using chemical bond theory of dielectric description. The chemical bonding characteristics and their relationship with thermal expansion property and compressibility are explored. The calculated values of linear thermal expansion coefficient (LTEC) and bulk modulus agree well with the available experimental values. The calculations reveal that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the lanthanides: the LTEC decreases from 6.80 to 6.62 10(-6)/K and the bulk modulus increases from 141 to 154 GPa when R goes in the order Gd, Tb Dy, Ho, Er, Tm, and Yb in the alpha-R2MoO6 series; while in the R2Mo2O7 series, the LTEC ranges from 6.80 to 6.61 10(-6)/K and the bulk modulus ranges from 147 to 163 GPa when R varies in the order Nd, Sm, Gd, Tb and Dy.

Structure and catalytic properties of magnesia-supported copper salts of molybdovanadophosphoric acid

The structure and stability of magnesia-supported copper salts of molybdovanadophosphoric acid (Cu2PMo11VO40) were characterized by different techniques. The catalyst was prepared in ethanol by impregnation because this solvent does not hurt texture of the water-sensitive MgO and Cu2PMo11VO40. The Keggin-type structure compound may be degraded partially to form oligomerized polyoxometalate when supported on MgO. However, the oligomers can rebuild as the Keggin structure again after thermal treatment in air or during the reaction. Meanwhile, the V atoms migrate out of the Keggin structure to form a lacunary structure, as observed by Fourier transform IR spectroscopy. Moreover, the presence of Cu2+ as a countercation showed an affirmative influence on the migration of V atoms, and the active sites derived from the lacunary species generated after release of V from the Keggin anion. The electron paramagnetic resonance data imply that V5+ autoreduces to V4+ in the fresh catalyst, and during the catalytic reaction a large number of V4+ ions are produced, which enhance the formation of O2- vacancies around the metal atoms. These oxygen vacancies may also improve the reoxidation function of the catalyst. This behavior is correlated to higher catalytic properties of this catalyst. The oxidative dehydrogenation of hexanol to hexanal was studied over this catalyst.

Effect of different VOPO4 phase catalysts on oxidative dehydrogenation of cyclohexane to cyclohexene in acetic acid

alpha(1)-VOPO4, alpha(II)-VOPO4 and beta-VOPO4 have been investigated as catalysts for the gas phase oxidative dehydrogenation (ODH) of cyclohexane to cyclohexene with the addition of acetic acid (HOAc) in the feeds in a fixed bed reactor. Different VOPO4 phases showed different acidity and reducibility. beta-VOPO4 phase is more active than alpha(I)-VOPO4 and alpha(II)-VOPO4 in the ODH without acetic acid addition. In the presence of acetic acid, the acidity of the catalyst may play an important role in the ODH process. Due to higher acidity, alpha(I)-VOPO4 phase catalyst gives better catalytic performances than alpha(I)-VOPO4 and beta-VOPO4 for the ODH of cyclohexane by adding of acetic acid in the reactants.