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1.
The structure of copper species, dispersed on nanostructured ceria(particles, rods and cubes), was analyzed by scanning transmission electron microscopy(STEM) and X-ray photoelectron spectroscopy(XPS). It was interestingly found that the density of surface oxygen vacancies(or defect sites), induced by the shape of ceria, determined the geometrical structure and the chemical state of copper species. Atomically dispersed species and monolayers containing few to tens of atoms were formed on ceria particles and rods owing to the enriched anchoring sites, but copper clusters/particles co-existed, together with the highly dispersed atoms and monolayers, on cubic ceria. The atomically dispersed copper sites and monolayers interacted strongly with ceria, involving a remarkable charge transfer from copper to ceria at their interfaces. The activity for the low-temperature watergas shift reaction of the Cu/CeO_2 catalysts was associated with the fraction of the positively-charged copper atoms, demonstrating that the active sites could be tuned by dispersing Cu species on shape-controlled ceria particles. 相似文献
2.
Effect of copper oxide on the catalytic activity of iron-chromia catalyst for water gas shift reaction 总被引:1,自引:0,他引:1
V. Idakiev D. Mihajlova B. Kunev A. Andreev 《Reaction Kinetics and Catalysis Letters》1987,33(1):119-124
It has been established that copper oxide promotes the catalytic activity of iron-chromia catalyst in the water gas shift reaction due to the formation of catalytically active aggregates. However, due to their gradual recrystallization and sintering into larger copper particles, the promoting effect sharply decreases.
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3.
T. P. Minyukova N. A. Baronskaya M. P. Demeshkina L. M. Plyasova T. M. Yurieva 《Kinetics and Catalysis》2016,57(2):224-228
The catalytic properties of a series of copper chromite ferrite samples with the composition CuCr2–xFexO4 (where x = 0–2) and a spinel-type structure in reactions with reducing (water gas shift reaction, WGSR) and oxidizing (the oxidation of hydrogen) reaction atmospheres were studied. The samples were obtained by the thermal decomposition of mixed hydroxo compounds. The distribution of Cu2+ ions in the tetrahedral and octahedral crystallographic positions of spinel, which depends on the Cr3+/Fe3+ ratio, affects the apparent activation energy (Ea) in both of the reactions. In WGSR, Ea is ~33 kJ/mol for CuCr2O4, in which Cu2+ ions mainly occupy tetrahedral positions, whereas Ea ≈ 100 kJ/mol for CuFe2O4, in which Cu2+ ions mainly occupy octahedral positions. In the reaction of hydrogen oxidation, Ea is ~71 kJ/mol for CuCr2O4 or ~42 kJ/mol for CuFe2O4. The value of Ea for the mixed chromite ferrites changes with the replacement of chromium ions by iron ions and, hence, with a ratio between the amounts of copper ions in the tetrahedral and octahedral oxygen positions of spinel. 相似文献
4.
Joseína Moutinho Tavares de Souza Maria do Carmo Rangel 《Reaction Kinetics and Catalysis Letters》2004,83(1):93-98
Aluminium-rich hematite was found to catalyze the water gas shift reaction but there is a compromise between the increase
in specific surface area and the intrinsic activity.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
The comparative studies of physicochemical properties of Cu-support catalysts (support = ZnO, Al2O3, Cr2O3, ZnAl2O4, FeAlO3, or CrAl3O6) and their catalytic activity in methanol synthesis and water gas shift reaction were the main goal of this work. The promotion
effect of copper addition in both reaction was proved. The formation of spinel type structure CuCr2O4, ZnAl2O4 and binary oxide CrAl3O6, FeAlO3 during calcination process was confirmed by XRD technique. Results showed that 20% Cu/FeAlO3 had the best performance in water gas shift reaction. The best selective and active catalyst in methanol synthesis was 20%
Cu/ZnAl2O4. 相似文献
6.
Herbert Nagorski Manfred J. Mirbach Marlis F. Mirbach 《Journal of organometallic chemistry》1985,297(2):171-176
The chromium hexacarbonyl catalyzed watergas shift reaction is accelerated by UV irradiation and inhibited by increased CO pressure. An activation energy of 30 kJ mol?1 has been determined for the photochemical and one of 145 kJ mol?1 for the thermal reaction. Light accelerates the conversion of Cr(CO)6 into [Cr(CO)5 formate]?, which is thermally activated, as evidenced by in situ IR and UV spectroscopy. 相似文献
7.
通过浸渍还原法制备了不同比例的Pt-Mo/SiO_2催化剂,采用X射线衍射、透射电镜、X射线近边吸收谱和X射线光电子能谱表征了Pt-Mo/SiO_2催化剂的组成、结构及价态.研究结果表明,少量MoO_x修饰Pt-Mo/SiO_2催化剂在低温水汽变换反应中表现出比Pt/SiO_2催化剂更高的催化活性,过量MoO_x包覆的Pt-Mo/SiO_2催化剂活性较低.低温水汽变换反应活性来自于Pt与表面MoO_x的界面协同作用,限域在Pt纳米颗粒表面的MoO_x表现出较低价态,高分散MoO_x纳米岛修饰的Pt纳米颗粒是低温水汽变换反应的活性结构. 相似文献
8.
Hydrogen gas has been detected in a closed system containing copper and pure anoxic water [P. Szakalos, G. Hultquist, and G. Wikmark, Electrochem. Solid-State Lett. 10, C63 (2007) and G. Hultquist, P. Szakalos, M. Graham, A. Belonoshko, G. Sproule, L. Grasjo, P. Dorogokupets, B. Danilov, T. Aastrup, G. Wikmark, G. Chuah, J. Eriksson, and A. Rosengren, Catal. Lett. 132, 311 (2009)]. Although bulk corrosion into any of the known phases of copper is thermodynamically forbidden, the present paper shows how surface reactions lead to the formation of hydrogen gas in limited amounts. While water cleavage on copper has been reported and investigated before, formation of molecular hydrogen at a single-crystal Cu[100] surface is here explored using density functional theory and transition state theory. It is found that although solvent catalysis seems possible, the fastest route to the formation of molecular hydrogen is the direct combination of hydrogen atoms on the copper surface. The activation free energy (ΔG(s)(?)(f)) of hydrogen formation in condensed phase is 0.70 eV, which corresponds to a rate constant of 10 s(-1) at 298.15 K, i.e., a relatively rapid process. It is estimated that at least 2.4 ng hydrogen gas could form per cm(2) on a perfect copper surface. 相似文献
9.
The possibility of metal-metal cooperativity in improving the yield of the homogeneous water gas shift reaction (WGSR) has been investigated through full quantum mechanical density functional theory calculations. The calculations indicate that bimetallic catalysts would be likely to be more highly active than mononuclear metal-based catalysts for the WGSR. The results have implications for the design of improved WGSR catalysts in the future. 相似文献
10.
R. P. Pant S. B. Halligudi R. S. Shukla D. K. Suri R. V. Mehta 《Reaction Kinetics and Catalysis Letters》1998,64(1):109-112
A ferrofluid consisting of colloidally dispersed magnetite particles in water was found to be an efficient selective catalyst
for water gas shift reaction at 15–25 atmosphere of CO pressure in the temperature range of 423–553 K where the products obtained
were only CO2 and H2. The reaction was studied as a function of variation of the concentration of catalyst, pressure of CO gas and temperature.
Kinetic parameters suggested a mechanism involving first order dependence in CO and catalyst concentrations. 相似文献
11.
Barrows SE 《Inorganic chemistry》2004,43(26):8236-8238
A novel mechanism for the gas-phase Fe(CO)(5) and base catalyzed water gas shift reaction has been examined. The reaction pathway described here is predicted at the B3LYP/6-31++G(d,p) level to be energetically competitive with the classic mechanism. The reaction path explored here involves the energetically barrierless formation of (CO)(4)FeCOOH(-) (the catalyst of the system) decarboxylation induced by the addition of CO to give (CO)(4)FeCHO, and evolution of H(2) upon addition of H(2)O to the (CO)(4)FeCHO intermediate. The energetic barriers predicted for the last two steps are 21.2 and 42.0 kcal/mol, respectively, using the B3LYP method. 相似文献
12.
David M. Vandenberg Toshishige M. Suzuki Peter C. Ford 《Journal of organometallic chemistry》1984,272(2):309-320
The water gas shift reaction, H2O + CO ? H2 + CO2, catalyzed homogeneously by a system based on tetrairidiumdodecacarbonyl (Ir4(CO)12) in alkaline 2-ethoxyethanol/water solution was examined at moderate temperatures (90–130°C) and pressures (PCO 0.5–2.0 atm). The catalytic reaction showed an approximate first-order dependence on base concentration and on the concentration of iridium. The catalytic cycle was shown to have a zero order dependence on the partial pressure of CO. An apparent activation energy of 10.7 kcal mol?1 was obtained from a linear Arrhenius plot based on hydrogen production over the temperature range 90–130°C. The predominant pathway of the reaction can be explained by a mechanism in which activation of CO by nucleophilic attack of hydroxide on the metal hydride species HIr4(CO)11? produces the dihydride species, H2Ir4(CO)102? in the rate-limiting step. Subsequent reaction of this anion with H2O gives H2 plus HIr4(CO)11? again. The complex Ir8(CO)202? is shown to be a catalytically poor component of the solution. The system has also been shown to be active toward the decomposition of formate. This pathway however, is concluded to make an insignificant contribution to the catalysis rate under water gas shift reaction conditions. 相似文献
13.
利用密度泛函理论(DFT)研究了不同掺杂量的Cu-Pt-Au催化剂性质及水煤气变换反应(WGSR)在催化剂表面上的反应机理。首先对Cu-Au和Pt-Au二元催化剂的稳定性和电子活性进行研究,发现Pt-Au催化剂的协同效应较优,稳定性更优,结合能为77.15 eV,d带中心为-3.18 eV。当将Cu继续掺杂到Pt-Au合金中构成Cu-Pt-Au三元催化剂时,Cu3-Pt3-Au(111)结合能为77.99 eV,且d带中心为-3.05 eV,表明其具有较优的稳定性和电子活性。探讨了WGSR在Cu3-Pt3-Au(111)上的反应历程,氧化还原机理因CO氧化的能垒达到4.84 eV而不易进行。CHO和COOH两个中间体为竞争关系,且形成CHO中间物时的能垒较小,因此,反应相对容易按照甲酸机理进行。 相似文献
14.
Scott Battersby Mikel C. Duke Shaomin Liu Victor Rudolph Joo C. Diniz da Costa 《Journal of membrane science》2008,316(1-2):46-52
In this work, we investigate the performance of metal (Cobalt) doped silica membranes in a membrane reactor (MR) configuration for the low temperature water gas shift (WGS) reaction. The membranes were hydrostable and showed activated transport even after 2 weeks exposure to steam. High CO conversions resulted in the H2 and CO partial pressures in the reaction chamber moving in opposite directions, thus favouring H2/CO separation to treble (5–15) from 150 to 250 °C. On the other hand, the separation of H2/CO2 remained relatively low (2–4) as the driving force for diffusion or partial pressure of these gases remained equal in the reaction chamber irrespective of the extent of conversion. Below approximately 40% CO conversion, the MR is ineffective as the H2 driving force for permeation was so low that H2/CO selectivity was below unity. Operating under equilibrium limited conversion (space velocities 7500 h−1) conditions, very high conversions in excess of 95% were observed and there were no significant advantages of the MR performance over the packed bed reactor (PBR). However, for higher throughputs (space velocities 38000 and 75000 h−1) conversion is affected by the reaction rate, and relatively enough H2 is removed from the reactor through the membrane. Increasing temperature to 250 °C as a function of the space velocity (75000 h−1) allowed for the CO conversion in the MR to shift up to 12% as compared to the PBR. 相似文献
15.
不同金属催化水煤气变换反应活性的Monte Carlo模拟研究 总被引:1,自引:0,他引:1
运用BOC-MP方法对Cu(110),Cu(111),Pd(111)和Au(111)等过渡金属催化的WGS反应的可能微观动力学步骤进行了详尽的能学数据计算,并结合MonteCarlo方法对WGS反应的表面氧化还原机理进行了计算机模拟。结果表明,Cu的催化活性优于Pd,Au的催化活性,并获得了相应金属上WGS反应的表观活化能及动力学指前因子(相对值);在此基础上,对该反应的结构敏感性进行了研究,发现该反应为一结构敏感反应,与实验结果相符。 相似文献
16.
Limin Zhou Yanyan Liu Shuling Liu Huanhuan Zhang Xianli Wu Ruofan Shen Tao Liu Jie Gao Kang Sun Baojun Li Jianchun Jiang 《Journal of Energy Chemistry》2023,(8):363-396
The water gas shift(WGS) reaction is a standard reaction that is widely used in industrial hydrogen production and removal of carbon monoxide. The improved catalytic performance of WGS reaction also contributes to ammonia synthesis and other reactions. Advanced catalysts have been developed for both high and low-temperature reactions and are widely used in industry. In recent years, supported metal nanoparticle catalysts have been researched due to their high metal utilization. Low-temperature c... 相似文献
17.
《Journal of Energy Chemistry》2016,(6)
Reverse water gas shift(RWGS) reaction can serve as a pivotal stage in the CO_2 conversion processes,which is vital for the utilization of CO_2.In this study,RWGS reaction was performed over Pt/CeO_2 catalysts at the temperature range of 200-500℃ under ambient pressure.Compared with pure CeO_2,Pt/CeO_2catalysts exhibited superior RWGS activity at lower reaction temperature.Meanwhile,the calculated TOF and E_a values are approximately the same over these Pt/CeO_2 catalysts pretreated under various calcination conditions,indicating that the RWGS reaction is not affected by the morphologies of anchored Pt nanoparticles or the primary crystallinity of CeO_2.TPR and XPS results indicated that the incorporation of Pt promoted the reducibility of CeO_2 support and remarkably increased the content of Ce~(3+) sites on the catalyst surface.Furthermore,the CO TPSR-MS signal under the condition of pure CO_2 flow over Pt/CeO_2catalyst is far lower than that under the condition of adsorbed CO_2 with H_2-assisted flow,revealing that CO_2 molecules adsorbed on Ce~(3+) active sites have difficult in generating CO directly.Meanwhile,the adsorbed CO_2 with the assistance of H_2 can form formate species easily over Ce~(3+) active sites and then decompose into Ce~(3+)-CO species for CO production,which was identified by in-situ FTIR. 相似文献
18.
以CuSO4.5H2O和MnSO4.H2O为原料,KOH和NaOH为沉淀剂制备了铜锰复合氧化物,考察了其变换反应催化性能,利用XRD、低温氮气吸附法、TG、H2-TPR等对所合成样品进行了表征。以KOH和NaOH为沉淀剂所得沉淀终产物的物相组成和织构明显不同,分别为层状结构碱式硫酸铜Cu4SO4(OH)6.H2O及无定形锰氧化物和Cu2+1O和Mn3O4混合物。两种物相组成和织构完全不同的沉淀终产物焙烧后都生成Cu1.5Mn1.5O4固熔体,在变换反应条件下均转化为Cu和MnO,但其催化性能却有明显差异。以NaOH为沉淀剂,得到以Cu2+1O和Mn3O4复合体为主的沉淀终产物,焙烧及还原后保持了较高的织构稳定性,提高了样品的活性和热稳定性。而以KOH为沉淀剂得到以层状结构碱式硫酸铜Cu4SO4(OH)6.H2O和无定形锰氧化物为主的沉淀终产物,在焙烧过程发生的演变极其复杂,削弱了铜锰组分协同效应,造成其活性和热稳定性极差。研究结果表明,NaOH作沉淀剂所制备样品的织构稳定性、催化活性显著高于以KOH作沉淀剂所制备样品,且热稳定性良好。 相似文献
19.
20.
A. A. Khassin T. P. Minyukova M. P. Demeshkina N. A. Baronskaya L. M. Plyasova G. N. Kustova V. I. Zaikovskii T. M. Yurieva 《Kinetics and Catalysis》2009,50(6):837-850
It was found experimentally that the solutions of Cr3+ nitrate and the nitrates of other metals that are the constituents of Cr-containing catalysts can be prepared by dissolving
a corresponding metal (for example, cast iron and electrolytic copper) in a solution of chromic anhydride and nitric acid
to reach the quantitative reduction of Cr6+ without the formation of nitrogen oxides. Analogously, the oxidation of Fe2+ cations to Fe3+ coupled with the reduction of hexavalent chromium can be performed. The precipitation of Fe3+, Cr3+, and Cu2+ ions at a ratio of Fe: Cr = 9 and a concentration of Cu2+ to 20 at % can result in the formation of a partially hydrated oxide with the hydrohematite structure—a dispersed and highly
defective oxide structure with a high specific surface area more than 300 m2/g and a higher thermal stability, as compared with the goethite phase (α-FeOOH). The dehydration of hydrohematite occurred
at a noticeable rate at temperatures higher than 400°C. Hydrohematite promoted with copper cations exhibited high activity
below 400°C; this can decrease the starting temperature of the adiabatic high-temperature WGSR to 300°C or below. 相似文献