共查询到20条相似文献,搜索用时 93 毫秒
1.
Xiao-Long Xu Jia Zhao Chun-Shan Lu Tong-Tong Zhang Xiao-Xia Di Shan-Chuan Gu Xiao-Nian Li 《中国化学快报》2016,27(6):822-826
Activated carbon-supported mercuric chloride(HgCl_2) is used as an industrial catalyst for acetylene hydrochlorination. However, the characteristic of easy sublimation of HgCl_2 leads to the deactivation o the catalyst. Here, we showed that the thermal stability of the Hg/AC catalyst can be evidently improved when Cs Cl is added into the Hg/AC catalyst. Compared with the pure Hg/AC catalyst, the sublimation rate of HgCl_2 from the Hg–Cs/AC catalyst decreased significantly and the Hg–Cs/AC catalyst showed bette catalytic activity and stability in the reaction. This promoting effect is related to the existence of cesium mercuric chlorides(Cs_xHg_yCl_(x+2y)) highlighted by XRD, HR-TEM and EDX analyses. Thus, reacting HgCl_2 with alkali chlorides to form alkali-mercuric chlorides may be a key to design highly efficient and thermally stable mercuric chloride catalyst for hydrochlorination reactions. 相似文献
2.
碱金属钾对Ni基催化剂纤维素水蒸气气化活性的影响 总被引:2,自引:0,他引:2
碱金属钾对Ni基催化剂纤维素水蒸气气化活性的影响 《燃料化学学报》2015,43(12):1433-1438
采用两段式催化气化方式研究了生物质热解气化过程中碱金属的挥发对Ni基催化剂活性的影响。实验结果表明,负载K盐的纤维素水蒸气催化气化过程中,K挥发后会在催化剂表面沉积,而少量K的存在和表面沉积不但能够提高镍基催化剂的抗积炭能力,而且有助于提高其催化活性,产生更多的氢气。然而纤维素中K的浓度过大,将会抑制Ni基催化剂的效果;K在催化剂上的沉积随催化剂循环次数的增加而增加,K的含量愈高,对催化剂的抑制效果愈明显,从而缩短了催化剂的使用寿命。 相似文献
3.
油剂混合区的工艺条件对催化裂化汽油改质的影响 总被引:1,自引:1,他引:0
利用连续式小型提升管催化裂化实验装置研究了原料预热温度、再生剂温度、油剂混合区温度和剂油比等油剂混合区的工艺条件对催化裂化汽油改质的影响规律。结果表明,降低再生剂温度、油剂混合区温度和剂油比均可以降低干气和焦炭的产率,同时也对催化裂化汽油改质的效果产生了影响。其中,再生剂温度对干气和焦炭产率影响最大;剂油比对催化裂化汽油改质的效果影响显著。降低再生剂温度、剂油比和油剂混合区温度一定程度上降低了烯烃转化率、异构烷烃增加率和芳烃增加率。提高原料预热温度可以一定程度上增加烯烃转化率、异构烷烃增加率和芳烃增加率。催化裂化汽油改质油剂混合区的最佳工艺条件为维持一定的反应温度和剂油比,并尽可能降低再生剂温度和提高原料预热温度。 相似文献
4.
Possible modes of deactivation of Jacobsen's Co-salen catalyst during the hydrolytic kinetic resolution (HKR) of epichlorohydrin were explored by UV-vis spectroscopy, X-ray absorption spectroscopy, and electrospray ionization mass spectrometry, combined with recycling studies. Although an active Co(III)-salen catalyst deactivated substantially after multiple cycles without regeneration, the catalyst maintained its +3 oxidation state throughout the runs. Thus, deactivation of Co-salen during HKR was not the result of Co reduction. The mass spectrum of a deactivated material showed that catalyst dimerization does not account for the loss of activity. Results from various catalyst pretreatment tests, as well as from catalysts containing various counterions (acetate, tosylate, chloride, iodide) indicated that the rate of addition of the Co-salen counterions to epoxide forming Co-OH during the reaction correlated with deactivation. The extent of counterion addition to epoxide was influenced by the exposure time and the nucleophilicity of the counterion. An oligo(cyclooctene)-supported Co-OAc salen catalyst, which was 25 times more active than the standard Co-salen catalyst, was recycled multiple times with negligible deactivation. 相似文献
5.
《Surface and interface analysis : SIA》2003,35(4):354-359
The distribution of platinum group elements (PGEs) and catalyst poisoning elements (Pb, Zn, P and S) on the surface of gasoline and diesel automobile catalysts was investigated within this study. Laser ablation–inductively coupled plasma mass spectrometry (LA–ICPMS) provides both the sensitivity and the spatial resolution required for the surface analysis of sectioned automobile catalysts, and scanning along channels reveals the distribution of longitudinal changes in PGE and catalyst poisoning elements. Changes in catalyst surface features were studied for fresh catalysts and after ageing of the catalyst up to 80 000 km for both types of catalysts studied. The PGEs in the gasoline catalyst were found to decrease at the front of the catalyst after ageing, whereas the diesel catalyst presented a more constant loss along the catalyst. The fraction of poisoning elements (Pb, P and Zn for the gasoline catalyst and P and Zn for the diesel catalyst) retained by the catalyst is distributed non‐uniformly over the length of the catalyst. This could indicate different ageing mechanisms for gasoline and diesel catalysts. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
Strieter ER Blackmond DG Buchwald SL 《Journal of the American Chemical Society》2003,125(46):13978-13980
A comparative kinetic examination of catalyst systems based on several monophosphinobiaryl ligands is reported. The bulk of the phosphine ligand controls the catalytic activity and the rate of catalyst activation with the catalyst based on 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl providing the greatest activity and fastest activation. In the case where catalyst activation is slow (i.e., use of the smaller ligands such as 2-dicyclohexylphosphino-2'-methylbiphenyl in combination with Pd(OAc)2) stirring the amine with the catalyst/base mixture prior to the commencement of the reaction increases the reaction rate along with the rate of catalyst activation. Kinetic isotope effects established that the catalyst activation process occurs through a beta-hydride elimination pathway. 相似文献
7.
E. I. Kapinus T. I. Viktorova T. A. Khalyavka 《Theoretical and Experimental Chemistry》2009,45(2):114-117
The effect of the concentration of disperse titanium-containing oxide photocatalysts on the decomposition of safranine in
aqueous solution was studied. The observed decomposition rate constant of safranine increases with increasing catalyst content
in the solution and reaches a maximum at catalyst concentration ≤3 g/L, after which this constant no longer depends on the
catalyst content. The plateau for the rate constant results from light scattering and narrowing of the reaction space due
to increased optical density of the solution. An increase in the specific catalyst surface is observed in the region of a
rising rate constant with increasing catalyst concentration, while no such dependence is found in the plateau region.
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 104-107, March-April, 2009. 相似文献
8.
Yu. V. Tsarev V. V. Kashnikov S. V. Krupin V. V. Kostrov 《Russian Journal of Applied Chemistry》2006,79(1):93-97
Catalytic oxidation of acetone on samples of a copper-containing catalyst with an ac electric field applied to the catalyst bed was simulated. The distribution of temperature across the catalyst bed was studied at varied delivered specific electric power, and kinetic parameters of the catalyst samples were determined. 相似文献
9.
10.
Um JM DiRocco DA Noey EL Rovis T Houk KN 《Journal of the American Chemical Society》2011,133(29):11249-11254
The asymmetric intermolecular Stetter reaction was investigated using the B3LYP and M06-2X functionals. Fluorination of a triazolium bicyclic catalyst had been found to significantly influence reaction yields and enantiomeric ratios. Computations indicate that the improved reactivity of the fluorinated catalyst is due to better electrostatic interactions between the nitroalkene and catalyst. Computational investigations of preferred conformations of the ground state catalyst and acyl anion equivalent, and the transition structures leading to both enantiomers of the products, are reported. 相似文献
11.
Xie Zaiku 《Reaction Kinetics and Catalysis Letters》2005,84(2):247-254
Summary The effects of calcination conditions on the properties of the catalyst for dehydrogenation of ethylbenzene were studied by using TG, DTA, and XRD. The formation temperature of polyferrite was higher than 600°C. The strength of the catalyst changed during calcination. Higher temperature enhanced the strength and improved the activity of catalyst. The calcination model has great influences on the catalyst performance. Multi-stage calcination improved the catalyst activity. 相似文献
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13.
以2,6-二氨基嘌呤(Hdap)为配体合成了Fe-Nx/C氧还原催化剂, 并优化了热处理温度和Fe含量. 对催化剂组成和结构进行了表征, 分析了配体Hdap在热处理过程中随温度的变化情况, 通过循环伏安法和线性扫描伏安法测试了催化剂的氧还原催化性能. 结果表明, 热处理温度为800℃, Fe质量分数为5%时, 催化剂活性最高. 吡啶N含量较高的配体有利于提高催化剂的活性, 配体中含S元素会增加催化剂的活性. 相似文献
14.
The reaction of dichloromethane with hydrogen fluoride in the presence of antimony chlorofluorides is studied in the setup
for liquid-phase synthesis. The reaction type, orders with respect to reactants and the catalyst, and Arrhenius parameters
are determined. The elemental composition of the catalyst for liquid-phase fluorination in the considered process is found.
The dynamics of the catalyst activity is studied. 相似文献
15.
《Journal of Energy Chemistry》2017,26(1):163-167
Adsorption state of catalyst on photoanode is an important factor on influencing the performance of dye-sensitized photoelectrochemical cells(DS-PECs) for water splitting. Photoanode TiO_2(1 + 2) was assembled with Ru(bpy)3phosphoric acid derivative(complex 1) as photosensitizer and complex 2 as water oxidation catalyst to compare with photoanode TiO_2(1 + 3). The photocurrent density of photoanode TiO 2(1 + 3) with catalyst 3 synthesized with only one end fixing on the surface of TiO_2 is about four-fold of the photoanode assembled with catalyst 2 fixing with two claws on the surface of TiO 2. The phenomenon should be caused by the littery arrangement and shorter distance of catalyst 2 from the active center of catalyst to TiO_2 on the surface of semiconductor which led to lowly efficient electron transfer. 相似文献
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17.
Numerical simulation of the ordered catalyst layer in cathode of proton exchange membrane fuel cells
A steady-state, one-dimensional numerical model based on cylindrical electrode structure is presented to analyze the performance of the ordered cathode catalyst layer in Proton Exchange Membrane Fuel Cells. The model equations account for the Tafel kinetics of oxygen reduction reaction, proton migration, oxygen diffusion in the cylindrical electrolyte and the gas pores, oxygen distribution at the gas/electrolyte interface. The simulation results reveal that ordered catalyst layers have better performance than conventional catalyst layers due to the improvements of mass transport and the uniformity of the electrochemical reaction rate across the whole width of the catalyst layer. The influences of oxygen diffusivity in gas phase and electrolyte, and the proton conductivity have been shown. The limitation by oxygen diffusion in gas phase drives the active region of the catalyst layer to the catalyst layer/gas diffuser interface. The limitation by proton migration confines the active region of the catalyst layer to the membrane/catalyst layer interface. The limitation due to oxygen diffusion in electrolyte film maintains the uniform distribution of the active region throughout the ordered catalyst layer. 相似文献
18.
E. F. Sutormina L. A. Isupova A. N. Nadeev V. A. Rogov V. P. Ivanov E. B. Burgina A. A. Budneva 《Kinetics and Catalysis》2009,50(6):892-898
The changes in the properties of the oxide monolith catalyst IK-42-1 for ammonia oxidation upon 3540-h-long operation as the
second stage of a UKL-7 industrial reactor were studied by X-ray diffraction, chemical analysis, secondary ion mass spectrometry,
temperature-programmed reduction, and IR spectroscopy. The spent catalyst shows a lower activity and a lower nitrogen oxide
selectivity than the initial catalyst: the decrease in the NO yield is about 25%. As the catalyst operates, the state of its
surface changes under the action of the reaction medium. The specific surface area of the catalyst decreases, and the total
pore volume increases, which can cause a slight decrease in the ammonia conversion and diminish the mechanical strength of
the monoliths. Under the ammonia oxidation conditions, there can be partial reduction of the catalyst surface and the local
formation of a spinel structure (spinel-like defects). Oxygen adsorbed on these areas/defects is characterized by a high activation
energy of desorption, which favors the reaction route yielding molecular nitrogen. According to IR spectroscopic data, the
spent catalyst has a lower concentration of active, coordinatively unsaturated Fe2+ sites of adsorption, which are responsible for ammonia oxidation into NO. The decrease in the number of active sites can
be due to both the breakdown of the solid solution of iron oxide in aluminum oxide during the reaction and the blocking of
these sites by silicon, alkali and alkaline-earth metal, chromium, and rhodium atoms present on the surface of the spent catalyst. 相似文献
19.
制备了三缺位Keggin型反应控制相转移催化剂[C7H7(CH3)3N]9PW9O34(记为Q9PW9),利用FT-IR、31P NMR、XRD和TG对催化剂进行了表征,并确定了反应的催化活性中心。 分析结果表明,催化剂Q9PW9在反应后其结构仍然得到了很好的保持,反应中形成的[C7H7(CH3)3N]9PW9O34 (O2)x活性中心使催化剂具有反应控制相转移功能。以H2O2水溶液为氧化剂,在氧化苯甲醇制备苯甲醛反应中,发现该催化剂具有良好的催化活性。当H2O2与苯甲醇的物质的量比为0.9时,苯甲醇的转化率为86.2%,苯甲醛的选择性≥99%。反应结束后催化剂以沉淀的形式析出,催化剂的回收率保持在86%左右。将催化剂循环使用三次,苯甲醇的转化率和催化剂的回收率均无明显变化,说明Q9PW9具有良好的稳定性。 相似文献
20.
Jurjen Meeuwissen Mark Kuil Dr. Alida M. van der Burg Albertus J. Sandee Dr. Joost N. H. Reek Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10272-10279
A procedure is described for the automated screening and lead optimization of a supramolecular‐ligand library for the rhodium‐catalyzed asymmetric hydrogenation of five challenging substrates relevant to industry. Each catalyst is (self‐) assembled from two urea‐functionalized ligands and a transition‐metal center through hydrogen‐bonding interactions. The modular ligand structure consists of three distinctive fragments: the urea binding motif, the spacer, and the ligand backbone, which carries the phosphorus donor atom. The building blocks for the ligand synthesis are widely available on a commercial basis, thus enabling access to a large number of ligands of high structural diversity. The simple synthetic steps enabled the scale‐up of the ligand synthesis to multigram quantities. For the catalyst screening, a library of twelve new chiral ligands was prepared that comprised substantial variation in electronic and steric properties. The automated procedures employed ensured the fast catalyst assembly, screening, and direct acquisition of samples for analysis. It appeared that the most selective catalyst was different for every substrate investigated and that small variations in the building blocks had a major impact on the catalyst performance. For two substrates, a catalyst was found that provided the product with outstanding enantioselectivity. The subsequent automated optimization of these two leads showed that an increase of catalyst loading, dihydrogen pressure, and temperature had a positive effect on the catalyst activity without affecting the catalyst selectivity. 相似文献