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A series of nanosized palladium catalysts supported by silica and polymers, prepared by the complex transformation method, were used for catalytic hydrogenation of nitrobenzene. It was found that both the thickness of the polymer layer and the size of the palladium particles would affect the catalysis. The results indicated that the reaction rate would be optimal when a polymer supporter formed a single layer on the silica surface. The catalytic activity of the catalyst would not simply increase with the decrease of the size of palladium particles. The effects of other conditions on the catalytic properties, such as the order during preparation of the catalyst, solvent, and the pH values, were also discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3661–3665, 2003 相似文献
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Palladium/silica catalysts of varying dispersities were submitted to the coking reaction with cyclopentane at 500°C. Temperature programmed oxidation curves reveal the presence of two peaks for carbon deposition on the metallic function: the first one near 250°C would correspond to coke deposited on palladium atoms of high coordination and the second one near 400°C would involve palladium atoms of low coordination. 相似文献
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Peter Miedziak Meenakshisundaram Sankar Nikolaos Dimitratos Jose A. Lopez-Sanchez Albert F. Carley David W. Knight Stuart H. Taylor Christopher J. Kiely Graham J. Hutchings 《Catalysis Today》2011,164(1):2278
A key discovery in the last two decades has been the realisation that gold, when prepared as supported nanoparticles, is exceptionally effective as an oxidation catalyst, particularly for the oxidation of alcohols. The catalytic efficacy is enhanced further by the alloying of gold with palladium. In this paper we study the effect of the method preparation of gold–palladium alloy nanoparticles supported on titania and investigate the activity of the materials for the selective oxidation of benzyl alcohol. We contrast impregnation and deposition–precipitation methods and demonstrate that the most active catalysts are prepared using the deposition–precipitation method. 相似文献
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The kinetics of degradation of cellulose triacetate in a dichloromethane-acetic anhydride mixture with perchloric or sulphuric acid catalyst was studied. Decrease in molecular weight with time was followed viscometrically using limiting viscosity numbers, calculated by a single-point method, and Mark-Houwink constants for the solvent mixture. Dependence of first-order rate constants on catalyst concentration and temperature was investigated and Arrhenius parameters, activation entropies and catalytic coefficients were obtained. A suggested reaction mechanism for degradation based on H+ and Ac+ (acetylium ion) acting as catalytic species is proposed. 相似文献
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钯触媒在蒽醌法生产双氧水的应用 总被引:1,自引:0,他引:1
根据国内双氧水生产装置上钯催化剂的使用情况,阐述了蒽醌法生产过氧化氢中所用钯催化剂的装填、活化、应用和再生等过程的优化控制和注意事项。提出了改善操作条件的办法,如温度、压力、工作液流量及循环氢化液流量等。提出了用蒸汽或有机溶剂使催化剂再生的方法。 相似文献
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Valmikanathan P. Onbattuvelli Willie E. Rochefort John Simonsen Seong‐Jin Park Randall M. German Sundar V. Atre 《应用聚合物科学杂志》2010,118(6):3602-3611
Effect of heating rate, Pd content, and synthesis method on the thermal stability of the ex situ and in situ Palladium/polycarbonate (Pd/PC) nanocomposites was investigated. TEM images revealed discrete Pd nanoclusters of about 5 and 15 nm sizes for 1 and 2 vol % ex situ nanocomposites, respectively. However, agglomerated Pd nanoclusters were noticed in the in situ samples, irrespective of the Pd content. The ex situ Pd/PC nanocomposites showed high onset temperature (Ti) for thermal degradation of PC than the in situ and pure PC samples. Pd content and heating rates were found to have a positive influence on the Ti and Tm (temperature at the maximum degradation rate occurs) of the Pd/PC nanocomposites. Thermal degradation of the PC was found to follow the first‐order kinetics in the Pd/PC nanocomposites. The activation energies associated with the degradation were determined by using the Kissinger method. These activation energies are used to construct the Master decomposition curve (MDC) and weight–time–temperature (α–t–T) plots that describe the time‐temperature dependence of the PC pyrolysis in the Pd/PC nanocomposites. These constructed α–t–T plots were validated with the data from isothermal measurements. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
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Zhenhua LI Weihan WANG Dongxue YIN Jing LV Xinbin MA 《Frontiers of Chemical Science and Engineering》2012,6(4):410
The syntheses of dimethyl oxalate (DMO) and diethyl oxalate (DEO) by CO coupling reaction in gaseous phase were investigated in a fixed bed reactor over Pd-Fe/Al2O3 catalyst. The catalytic performance was characterized by CO conversion, space-time yield (STY) and selectivity of DMO (or DEO). The results showed that over Pd-Fe/Al2O3 catalyst, the STY of DMO was higher than that of DEO under the same reaction conditions. The optimum reaction temperatures for synthesizing DMO and DEO were 403 K and 393 K, respectively, at the molar ratio 1 ∶ 1 of alkyl nitrite to CO. The difference in synthesizing DMO and DEO on the same catalyst was attributed to the decomposition performances of methyl nitrite (MN) and ethyl nitrite (EN), as density functional theory (DFT) calculation showed that EN decomposed more easily than MN. 相似文献
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SiO_2-TiO_2负载钯催化剂的制备及其催化Suzuki反应研究 总被引:1,自引:0,他引:1
以正硅酸乙酯和钛酸正丁酯作前体,通过均匀沉淀法制备了SiO2-TiO2复合氧化物,并采用X射线粉末衍射(XRD)对复合氧化物进行了表征。采用浸渍制备了复合氧化物负载的钯催化剂Pd/SiO2-TiO2,并考察了负载催化剂在Suzuki反应中的催化性能。当投料摩尔比n(Pd)∶n(PhBr)∶n[PhB(OH)2]∶n(K2CO3)为1∶70∶105∶140,Ti/Si摩尔比和钯质量分数分别为0.5和2.0%时,回流反应10 h,联苯产率达92.8%。负载催化剂通过简单过滤即可回收利用,在5次循环使用过程中,催化活性除第1次有明显降低外,其后基本保持不变。 相似文献
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Nicholas F. Dummer Salem Bawaked James Hayward Robert Jenkins Graham J. Hutchings 《Catalysis Today》2011,160(1):2
Supported gold, palladium and gold–palladium catalysts have been used to oxidatively dehydrogenate cyclohexane and cyclohexenes to their aromatic counterpart. The supported metal nanoparticles decreased the activation temperature of the dehydrogenation reaction. We found that the order of reactivity was Pd ≥ Au–Pd > Au supported on TiO2. Attempts were made to lower the reaction temperature whilst retaining high selectivity. The space-time yield of benzene from cyclohexane at 473 K was determined to be 53.7 mol/kgcat/h rising to 87.3 mol/kgcat/h at 673 K for the Pd catalyst. Increasing the temperature in this case improved conversion at a detriment to the benzene selectivity. Oxidative dehydrogenation of cyclohexene over AuPd/TiO2 or Pd/TiO2 catalysts was found to be very effective (conversion >99% at 423 K). These results indicate that the first step in the reaction sequence of cyclohexane to cyclohexene is the slowest step. These initial results suggest that in a fixed-bed reactor the oxidative dehydrogenation in the presence of oxygen, palladium and gold–palladium catalysts are readily able to surpass current literature examples and with further modification should yield even higher performance. 相似文献
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The influence of a chitosan application on wool fabric before a treatment with a proteolytic enzyme has been investigated. The enzymatic treatment enhances whiteness and confers shrink resistance to wool, but an increase in the enzyme concentration leads to a detrimental effect on the physicomechanical properties. A chitosan treatment before the enzymatic treatment additionally improves the shrink resistance and increases the weight loss. To better investigate the role played by the chitosan, surface‐related properties, such as the friction coefficient, the compressional behavior (compressibility, linearity of compression, and thickness), the wearing resistance (weight loss after abrasion), the bursting resistance (bursting strength and deformation), and surface topography, have been studied. The results suggest that the chitosan pretreatment reduces the damage caused by the subsequent enzymatic treatment. They also imply a protective effect of the bursting and wearing resistance, which prevent excessive weight loss due to abrasion. A significant influence of the wool fiber cell membrane complex on the surface‐related properties has been demonstrated through regression analysis and scanning electron microscopy observations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1938–1946, 2005 相似文献
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Ahmed A. Galhoum Mohammad G. Mahfouz Nabawia A. Gomaa Sayed S. Abdel-Rehem Asem A. Atia Thierry Vincent 《分离科学与技术》2015,50(18):2776-2789
Magnetic-chitosan nanoparticles, functionalized with cysteine, were synthesized and characterized by element analysis, FT-IR, XRD, TEM, and vibrating sample magnetometry. The sorbent was tested for U(VI) recovery, considering:
a. pH effect,
b. sorption isotherms (fitted by Langmuir equation), and
c. uptake kinetics (modeled using the PSORE).
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以聚苯乙烯树脂为载体、二环己胺为配体制备聚苯乙烯负载胺钯催化剂。采用XPS、XRD、TG、DTA和SEM等方法对其进行表征,针对不同催化体系探讨丙烯酸、苯乙烯与芳基碘的Heck反应的催化性能。结果表明,高分子胺配体与钯之间形成配位作用,制备的催化剂在室温~200 ℃有较好的热稳定性。该负载型催化剂在N2氛围只需少量的催化剂就能较好地催化丙烯酸、苯乙烯与芳基碘的Heck反应,较高收率地生成取代的反式肉桂酸和1,2-二苯基乙烯。 相似文献
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以硼杂碳包镍(Ni@BC)为载体,采用乙醇还原前驱体H_2PdCl_4法制备了一种新型磁可分离Pd/Ni@BC催化剂,并对其进行AAS、TEM、XRD和XPS表征,选取苯甲醇需氧氧化为探针反应,考察催化剂用量、反应温度和反应时间对催化性能的影响,研究催化剂对其他芳香醇的催化性能和循环使用性能。AAS结果表明,Pd负载质量分数为9.1%,与理论负载量一致。TEM结果显示,Pd纳米颗粒均匀分散在载体表面,平均粒径为4 nm。XRD和XPS结果均表明,催化剂的活性物种为Pd0。在反应温度80℃、O2_压力101.325 k Pa(流速20 m L·min~(-1))、CH_3CN为溶剂和K_2CO_3为碱性助剂条件下,Pd/Ni@BC对多种芳香醇的氧化反应表现出很高的催化活性和选择性,能将苯甲醇、对甲基苯甲醇、对乙基苯甲醇、对异丙基苯甲醇、肉桂醇、安息香、二苯甲醇以及邻甲基苯甲醇等定量转化为相应的醛或酮。催化剂重复使用5次,苯甲醇转化率由97.3%降至78.9%,Pd的少量脱落和部分氧化是催化剂活性降低的主要原因。 相似文献
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Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina. 相似文献