Effect of Preparation Conditions on Ag Catalysts for Ethylene Epoxidation

The effect of calcination of silver catalysts supported on foamed monoliths was examined for the epoxidation of ethylene. Previous results suggested that calcination at 673 K for 3 h would give a maximum conversion. Further study revealed that calcination for >3 h reduced the catalyst surface area and therefore the conversion seen in reactor studies. This phenomenon has been attributed to sintering, with the migration of Ag from mesopores of the catalysts to macropore regions and the eventual formation of a Ag film covering the walls of the macropores. Studies of the metal loading showed that a tradeoff exists between metal loading and calcination time. Increasing the amount of silver can have a detrimental effect on catalysts calcined for 12 h, however the opposite trend, an increased conversion with higher loadings, was observed for catalysts calcined for 2 h. These results imply that the sintering of Ag can play a dramatic effect on catalyst design for optimum performance.     

X-Ray Absorption and Photoemission Studies of the Active Oxygen for Ethylene Epoxidation over Silver

Activation of clean polycrystalline silver by a C₂H₄ + O₂ reaction mixture has been studied by XANES, XPS, and UPS. In situ monitoring of the O K-edge XAS spectrum of the pre-treated silver surface revealed a broad signal at 10–20 eV above the threshold. The comparison of the X-ray absorption spectra with O 1s and valence band photoemission data allowed us to attribute this XAS signal to electrophilic oxygen (E _b(O 1s) = 530.4 eV) which is known to be active in ethylene epoxidation. The complete absence of XAS features in the photon energy range typical for ^* and ^* transitions of molecular oxygen (530–535 eV) indicates both the atomic origin of the electrophilic oxygen and the absence of molecular species on the catalyst surface under the present reaction conditions.     

On the Mechanism of Ethylene Epoxidation

The epoxidation of olefins, while of considerable economic importance, forms a challenging problem to fundamental research in catalysis. When surveying the vast quantity of published material [1-6] two facts appear relevant.     

乙烯环氧化助催化作用的研究──多晶银表面化学修饰法

根据多晶银（电解银）表面吸附态氧主要是吸附态原子氧和次表层溶解氧的特性，探索并证实了电解银表面具有乙烯环氧化反应活性，从而研究了Ｂａ和Ｃｓ化合物修饰电解银表面对乙烯氧化反应的助催化作用．Ｂａ增加了活性，Ｃｓ降低了活性，但增大了环氧乙烷的选择性．对比了负载银添加Ｂａ和Ｃｓ化合物后的助催化性能，获得了一致的结果．表明电解银表面化学修饰可作为选择和研究Ａｇ助催化剂的一种合理而简便的手段．     

乙烯环氧化助催化作用的研究——多晶银表面化学修饰法

根据多晶银(电解银)表面吸附态氧主要是吸附态原子氧和次表层溶解氧的特性,探索并证实了电解银表面具有乙烯环氧化反应活性,从而研究了Ba和Cs化合物修饰电解银表面对乙烯氧化反应的助催化作用。Ba增加了活性,Cs降低了活性,但增大了环氧乙烷的选择性;对比了负载银添加Ba和Cs化合物后的助催化性能,获得了一致的结果。表明电解银表面化学修饰可作为选择和研究Ag助催化剂的一种合理而简便的手段。     

银催化剂在乙烯环氧化反应中的应用研究进展

银催化剂因其优异的选择性、催化活性及热稳定性能在环氧乙烷工业中得到了广泛的应用。本文从银催化剂制备、银催化剂载体的发展两个方面概述银催化剂在乙烯环氧化反应中的应用,以期对银催化剂在乙烯环氧化反应中的应用有深入的了解。     

催化分子氧环氧化环己烯的研究进展

介绍了分子氧的构型、催化烯烃环氧化机理及其催化环氧化环己烯的研究进展,提出以分子氧为氧源,催化环氧化环己烯的关键在于高效催化剂的制备及廉价易得还原剂的筛选。     

以分子氧为氧源催化丙烯环氧化制环氧丙烷研究进展

环氧丙烷是重要的基础化工原料。主要工业生产方法有氯醇法和Halcon法。氯醇法环境污染严重 ,急待改进 ;Halcon法产生大量联产品 ,且基本建设投资巨大。为了满足环境和经济等方面的要求 ,以分子氧为氧源的丙烯催化环氧化是最理想的生产方法 ,目前正处于研究阶段。文中对近十年来的研究进展做了综述     

Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen

Carbon templated mesoporous vanadium MFI catalysts with different Si/V ratios were successfully synthesized using microwave irradiation. X-ray diffraction studies revealed the formation of more crystalline MFI structures. SEM and TEM imaging also showed well ordered zeolite single crystals having mesoporosity. The N₂ sorption isotherm showed the formation of bimodal mesoporous zeolites. FT-IR studies showed absorbance around 970 cm^?1 corresponding to Si–O–V stretching vibration and the UV–Vis studies revealed strong peaks in the range of 230–340 nm which is related to the presence of tetrahedral V⁵⁺ state. The catalytic activity of the microwave synthesized catalysts was evaluated for epoxidation of styrene using molecular oxygen. The catalysts exhibited 20–40% styrene conversion with 60–75% epoxide selectivity. With increasing Vanadium content, the conversion as well as the selectivity was observed to increase. The catalyst could be recycled for three cycles without a loss in activity.     

第二代氧气法乙烯氧氯化制二氯乙烷催化剂

采用共沉淀法,加入第二组分和第三组分作为助催化剂制备的Cu/Al2O3催化剂,用于流化床氧气法乙烯氧氯化制二氯乙烷反应,可以有效地抑制乙烯深度氧化生成二氧化碳反应,提高二氯乙烷的纯度。在国内现有的两套20万t/a的氯乙烯生产装置上推广使用该催化剂,将收到可观的经济效益。同时,使用此催化剂生成的二氧化碳和其它氯化物较少,有利于环境保护。     

低温氧等离子体处理对芳纶表面性能的影响

以氧气对芳纶Nomex纱线进行等离子体处理后发现,芳纶纱线的拉伸强力略有增加。利用x-射线光电子能谱（XPS）分析等离子体处理前后芳纶纱线表面的元素组成变化,发现氧气等离子体处理后在纱线的表面引入了-COOH,纱线表面碳元素的含量下降,总的含氧基团量（-C—OH,-C=0,-0-C-O-,-COOH）增加。扫描电镜（SEM）观察发现,氧等离子体处理对芳纶纱线的表面有明显的刻蚀作用。     

Effect of Surface Activation Treatment on Pt/C Catalyst for Electrooxidation of Ethylene Glycol and Adsorbed CO

It was reported for the first time that the electrocatalytic activity of the Pt/C electrode for the oxidation of ethylene glycol (EG) could be dramatically improved after the new surface treatment of the Pt/C electrode. It was also found that the surface treatment of the Pt/C electrode could greatly promote the electrooxidation of CO adsorbed on the Pt/C electrode. Promoting the electrooxidation of CO would lead to the acceleration of the electrooxidation of EG because CO is an intermediate product of the oxidation of EG and it would be strongly adsorbed on the Pt catalyst, leading the poison of the Pt/C catalyst.     

Effect of Surface Concentration of Lu on Oxygen Permeation of Polycrystalline Alumina at High Temperatures

The effect of Lu surface concentration on oxygen permeation in polycrystalline α‐alumina wafers was determined at 1773 K under limited oxygen potential gradients (Δ), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [ (I) ?  (II)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a Δ generated by a combination of low values, the Lu‐coating on the (I) [ (II)] surface decreased [increased] the oxygen permeability constants. When Δ was the result of a combination of high values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu‐coating on the (I) surface. The analysis of mass transfer parameters, such as the chemical potentials, GB diffusion coefficients, and fluxes of aluminum and oxygen in the wafers, suggested that ambient oxygen molecules were effectively attracted toward Lu‐coated surfaces exposed to low‐ environments, leading to a change in oxygen permeability.     

The Effect of Filler Loading and Epoxidation on Paper-Sludge-Filled Natural Rubber Composites

The effect of filler loading and epoxidation on curing characteristics, dynamic properties, tensile properties, morphology, and rubber-filler interactions of paper-sludge-filled natural rubber compounds have been studied. Two different types of natural rubber, SMR L and ENR 50, having 0% and 50% of epoxidation and conventional vulcanization were used. Paper sludge was used as a filler and the loading range was from 0 to 40 phr. Compounding was carried out using a laboratory-sized two-roll mill. The scorch time for both rubber compounds decreased with filler loading. The cure time was found to decrease with increasing filler content for SMR L vulcanizates, whereas for ENR 50, the cure time seemed to be independent of the filler loading. Dynamic properties, i.e., maximum elastic torque, viscous torque, and tan delta, increase with filler loading in both grades of natural rubber. Results also indicate that both rubbers show increment in tensile modulus but inverse trend for elongation at break and tensile strength. However, for a fixed filler loading, ENR 50 compounds consistently exhibit higher maximum torque, modulus at 100% elongation, and modulus at 300% elongation, but lower elongation at break than SMR L compounds. In the case of tensile strength, ENR 50 possesses higher tensile strength than SMR L at 10 to 20 phr, but the difference is quite small at 30 and 40 phr. These findings might be associated with better rubber-filler interaction between the polar hydroxyl group of cellulose fiber and the epoxy group of ENR 50.     

乙烯掺杂对硅薄膜沉积速率和形貌的影响

采用APCVD工艺用硅烷和乙烯为原料在620℃沉积硅薄膜.用AFM观察薄膜表面形貌,用SEM扫描截面测量薄膜厚度.FTIR光谱表明薄膜中存在Si-C.研究了C2H4/SiH4摩尔比对膜厚的影响,随着C2H4/SiH4的增大,薄膜的沉积速率降低,表明乙烯掺杂会抑制薄膜生长,同时乙烯的加入减弱了颗粒的异常长大.     

Epoxidation by Layered Double Hydroxide-Hosted Catalysts. Catalyst Synthesis and Use in the Epoxidation of R-(+)-Limonene and (−)-α-Pinene Using Molecular Oxygen

A novel chiral sulphonato–salen–manganese(III) complex has been intercalated into a Zn(II)–Al(III) layered double hydroxide (LDH) host to produce a stable heterogeneous epoxidation catalyst. Powder X-ray diffraction, IR and UV–Visible (solid) spectroscopy and TGA confirmed the successful intercalation of the Mn complex within the LDH gallery height. The intercalated sulphonato–salen–manganese(III) complex was found to be an effective heterogeneous catalyst for the stereoselective epoxidation of R-(+)-limonene and (?)-α-pinene at room temperature and using molecular oxygen at atmospheric pressure as oxidant. At close to 100% conversion, R-(+)-limonene was converted into the corresponding epoxide with 93% selectivity and 43% de (diastereomeric excess), whereas (?)-α-pinene was converted with 93% selectivity and 98% de. The catalyst could be recycled without loss of efficiency.     

Determination of Surface Areas of Active Carbons by Retention of Ethylene Glycol and Ethylene Glycol Monoethyl Ether

Abstract

Experiments of ethylene glycol and ethylene glycol monoethyl ether retention on some active carbons were carried out to measure the surface areas of the carbons. Some differences were observed between nitrogen-specific surface area values and those obtained from ethylene glycol retention. However, since the differences decreased through an increase of surface oxygen content as a result of treatment of the carbons with H₂O₂, it was evident that ethylene glycol retention depended upon the surface oxygen content. Also, the surface area values obtained from retention of ethylene glycol monoethyl ether did not depend upon the surface oxygen content. Measurements of the ethylene glycol monoethyl ether retention process could be performed in a shorter time than the equivalent ethylene glycol retention measurements.     

流动型态对乙苯氢化过氧化物与丙烯的环氧化的影响

用乙苯氢过氧化物氧化丙烯制取环氧丙烷是目前生产环氧丙烷最有前途的工艺路线之一。为了选择在工艺上实现该反应的最佳装置,本文从环氧化反应的动力学模型出发,建立了活塞流、单级理想混合与多级理想混合环氧化反应器的数学模型,讨论了各种流动型态对该反应的影响。分析表明,多级理想混合环氧化反应器是较理想的工业装置,并指出了适合该装置的最佳操作条件。 在四级理想混合反应装置上,对多级理想混合环氧化反应器的数学模型进行了实验验证,实验结果与计算值得到了较好的吻合。     

乙烯含量对三元乙丙橡胶性能的影响

研究乙烯含量对三元乙丙橡胶(EPDM)性能的影响。结果表明:乙烯含量对EPMD胶料的门尼粘度和硫化特性无明显影响;随着乙烯含量的增大,EPDM硫化胶的硬度、拉伸强度、撕裂强度和回弹值总体呈增大趋势,低温性能变差。