Effect of support and acidity of catalyst on the direct oxidation of ethylene to acetic acid

The selective oxidation of ethylene to acetic acid was investigated on Pd-acid/support catalyst system. The catalytic activity is influenced strongly by the acidity of the catalyst. The stronger the catalyst acidity the higher the catalytic activity. The nature of the support also influences the activity of the catalyst substantially. The catalyst has highest activity when it exhibits highest acidity on silica.

Gas phase catalytic partial oxidation of toluene in a microchannel reactor

Gas phase partial oxidation of toluene over V/Ti oxide catalysts has been successfully performed in a microchannel reactor, which provides very good mass and heat transfer conditions. With the elimination of hot spots, which are known as the most negative factors for partial oxidation of hydrocarbons, steady and uniform reaction conditions can be achieved in the catalyst bed by using, the microreactor. Since the best performance of the catalysts might be exploited, the selectivity of partial oxidation products of toluene has remarkably increased compared to the traditional packed fixed-bed reactor, even without the bother of modifying the catalysts, diluting the reactants or catalysts with inert contents to avoid hot spots or improve the diffusion and mixing. Furthermore, in virtue of its inherent safety features, when using pure oxygen as oxidant, the reactions were handled safety within the explosion limits in the microreactor. With TiO2 carried V2O5 as catalysts, the total selectivity of benzaldehyde and benzoic acid reaches around 60%, and the toluene conversion is about 10%. The conversion can go up without violent decline of selectivity, unlike most fixed bed reactors. Space time yield of 3.12 kg h(-1) L-1 calculated on the basis of the channel volume has been achieved. The influence of operating conditions has been investigated in detail in the microreactor. (c) 2005 Elsevier B.V. All rights reserved.

Selective oxidations on recoverable catalysts assembled in emulsions

Catalysts assembled in emulsions are found to be potentially recoverable and efficient for a number of catalytic reactions. The catalysts composed of polyoxometalate anions and quaternary ammonium cations have been designed and synthesized according to the catalytic reactions and by optimizing the structures of cations and anions. The catalysts act essentially as surfactants, which are uniformly distributed in the interface of the emulsion droplets, and accordingly behave like homogeneous catalysts. The catalysts show remarkable selectivity and activity in the oxidation of sulfur-containing molecules to sulfones in diesel and the selective oxidation of alcohols to ketones, using H2O2 as oxidant. For an example, the catalyst demonstrated over 96% efficiency of H2O2 and similar to 100% selectivity to sulfones for the selective oxidation of sulfur-containing molecules in real diesel. Moreover, the catalysts can be separated and recycled by a simple demulsification and re-emulsification.

Femtosecond filamentation and supercontinuum generation in silver-nanoparticle-doped water

The authors report the investigation of filament and supercontinuum generation by focusing a femtosecond laser beam into water doped with silver nanoparticles. The silver nanoparticles enhance the nonlinear optical response of water, leading to broadening of supercontinuum spectra in self-focused femtosecond filaments. During the propagation of the supercontinuum light in the filament, the silver nanoparticles preferentially scatter the short-wavelength light near the plasmon resonant wavelength peak, followed by the scattering of the long-wavelength light. Thus, a side view of the filament shows a full-color spectrum in the visible range, which is herein called "rainbow filament." (c) 2007 American Institute of Physics.

Enzymatic activities in constructed wetlands and di-n-butyl phthalate (DBP) biodegradation

The bioaccumulation of phthalate acid esters (PAEs) from industrial products and their mutagenic action has been suggested to be a potential threat to human health. The effects of the most frequently identified PAE, Di-n-butyl phthalate (DBP), and its biodegradation, were examined by comparison of two small scale plots (SSP) of integrated vertical-flow constructed wetlands. The influent DBP concentration was 9.84 mg l(-1) in the treatment plot and the control plot received no DBP. Soil enzymatic activities of dehydrogenase, catalase, protease, phosphatase, urease, cellulase, beta-glucosidase, were measured in the two SSP after DBP application for 1 month and 2 months, and 1 month after the final application. Both treatment and control had significantly higher enzyme activity in the surface soil than in the subsurface soil (P < 0.001) and greater enzyme activity in the down-flow chamber than in the up-flow chamber (P < 0.05). In the constructed wetlands, DBP enhanced the activities of dehydrogenase, catalase, protease, phosphatase and inhibited the activities of urease, cellulase and beta-glucosidase. However, urease, cellulase, beta-glucosidase activities were restored 1 month following the final DBP addition. Degradation of DBP was greater in the surface soil and was reduced in sterile soil, indicating that this process may be mediated by aerobic microorgansims. DBP degradation fitted a first-order model, and the kinetic equation showed that the rate constant was 0.50 and 0.17 d(-1), the half-life was 1.39 and 4.02 d, and the r(2) was 0.99 and 0.98, in surface and subsurface soil, respectively. These results indicate that constructed wetlands are able to biodegrade organic PA-Es such as DBP. (c) 2005 Elsevier Ltd. All rights reserved.

Persistent organic pollutants in water and surface sediments of Taihu Lake, China and risk assessment

Organic pollutants, especially persistent organic pollutants were examined in the water and surface sediments of Taihu Lake, China. Both 12 water and 12 sediment samples were collected over the lake. C-18 solid-phase extraction technique was applied to extract organic pollutants in collected water samples. Soxhlet extraction procedure was used to extract organic pollutants in sediment samples. The analysis was performed by GC-MS controlled by a Hewlett Packard chemstation. Two hundred and seventy-three kinds of organic chemicals in water were examined, 200 more than that detected in 1985; 188 kinds of chemicals in sediments were detected as well. Among them 21 kinds of chemicals belong to priority pollutants as well as 17 kinds to be the endocrine disruptors. The concentrations of the pollutants were more than 2 times higher than that in 1985. The possible source and relation to anthropogenic activity were discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

Photonic switch and NOT logic gate based on the hybrid integration of a GaAsVCSEL and a GaAs MISS

The hybrid integrated photonic switch and not logic gate based on the integration of a GaAs VCSEL (Vertical Cavity Surface Emitting Lasers) and a MISS (Metal-Insulator-Semiconductor Switches) device are reported. The GaAs VCSEL is fabricated by selective etching and selective oxidation. The Ultra-Thin semi-Insulating layer (UTI) of the GaAs MISS is formed by using oxidation of A1As that is grown by MBE. The accurate control of UTI and the processing compatibility between VCSEL and MISS are solved by this procedure. Ifa VCSEL is connected in series with a MISS, the integrated device can be used as a photonic switch, or a light amplifier. A low switching power (10 mu W) and a good on-off ratio (17 dB contrast) have been achieved. If they are connected in parallel, they perform a photonic NOT gate operation.

Influence of dielectric properties of a substrate upon plasmon resonance spectrum of supported Ag nanoparticles

Plasmon resonance spectra of supported Ag nanoparticles are studied by depositing the particles on different substrates. It was found that the dielectric properties of the substrates have significant effects on the spectral line shape, except the resonance frequency. Beyond the plasmon resonance band, the spectral shape is mainly governed by the dielectric function, particularly its imaginary part, of the substrate. The plasmon resonance band, on the other hand, may be severely distorted if the substrate is absorbing strongly.

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.