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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. 相似文献
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X-Ray Absorption and Photoemission Studies of the Active Oxygen for Ethylene Epoxidation over Silver
V.I. Bukhtiyarov M. Hävecker V.V. Kaichev A. Knop-Gericke R.W. Mayer R. Schlögl 《Catalysis Letters》2001,74(3-4):121-125
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. 相似文献
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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. 相似文献
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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. 相似文献
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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。 相似文献
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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。 相似文献
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以分子氧为氧源催化丙烯环氧化制环氧丙烷研究进展 总被引:2,自引:0,他引:2
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 相似文献
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Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen 总被引:1,自引:0,他引:1
Krishna Mohan Jinka Hari C. Bajaj Raksh V. Jasra Eko Adi Prasetyanto Sang-Eon Park 《Topics in Catalysis》2010,53(3-4):238-246
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. 相似文献
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第二代氧气法乙烯氧氯化制二氯乙烷催化剂 总被引:1,自引:0,他引:1
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。 相似文献
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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. 相似文献
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Masashi Wada Tsuneaki Matsudaira Takeharu Kato Satoshi Kitaoka 《Journal of the American Ceramic Society》2013,96(7):2322-2329
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. 相似文献
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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. 相似文献
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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. 相似文献
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《分离科学与技术》2012,47(12):1687-1693
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. 相似文献
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