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Amaya Romero Agustín Garrido Antonio Nieto-Mrquez Paula Snchez Antonio de Lucas Jos Luis Valverde 《Microporous and mesoporous materials》2008,110(2-3):318-329
In order to study the influence of the metal phase in the carbon yield and structural characteristics of carbon nanofibers (CNFs) synthesized by CVD over supported catalysts, different catalysts were prepared using iron, cobalt and nickel as active metal and zeolites Y and mordenite as support. The results showed that the metal precursor produced a great influence on the catalytic activity, fact that could be explained in according to the different solubility of carbon in the metals or in the differences in the diffusion and segregation of carbon through the metal particles. Characterization data of the solid carbon products revealed unique structures and textural properties as well as crystalline conditions on function of metal used. Additionally, support-metal interaction was evaluated, where experiments with similar nickel load over Y and mordenite zeolites were carried out, finding higher carbon yields and more ordered structures when Y zeolite was used. 相似文献
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Partial oxidation of methane to synthesis gas over some titanates based perovskite oxides 总被引:1,自引:0,他引:1
Takashi Hayakawa Arnfinn G. Andersen Masao Shimizu Kunio Suzuki Katsuomi Takehira 《Catalysis Letters》1993,22(4):307-317
Ca1–x
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TiO3-based mixed oxide catalysts containing chromium, iron, cobalt or nickel were prepared and used in the oxidation of methane. The catalyst containing cobalt or nickel showed high activity for the synthesis gas production from methane. In the case of nickel containing catalyst, nickel oxide originally separated from the perovskite structure was easily reduced to nickel metal, which showed synthesis gas production activity. In the case of the cobalt containing catalyst, pretreatment with methane was required for high activity. Reduced metallic cobalt was formed from the perovskite structure, which revealed relatively high selectivity for the oxidative coupling of methane, and afforded synthesis gas production. Both the catalysts also catalyzed carbon dioxide reforming of methane and especially both high activity and selectivity were observed over the nickel containing catalyst. 相似文献
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采用骨架钴和骨架镍催化剂加氢还原制备糠醇的研究 总被引:3,自引:1,他引:2
从钼、铬、铜和铁中筛选金属铬和铁作为助催化剂加入骨架钴或骨架镍催化剂,铬和铁的量分别为催化剂质量的3%和1%。在100~120℃、10~12MPa条件下,用上述骨架钴或骨架镍催化剂在乙醇溶剂中,氢化还原糠醛制备糠醇。用骨架镍催化剂,反应产物含有785%的糠醇和196%的四氢糠醇;用骨架钴催化剂,反应产物含有988%的糠醇和08%的四氢糠醇,收率94%。在无乙醇溶剂条件下,反应产物含有905%的糠醇、03%的四氢糠醇和92%的糠醛。在180℃条件下,反应产物含有908%的糠醇和89%的四氢糠醇。 相似文献
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Ahmad Tavasoli Mariane Trépanier Reza M. Malek Abbaslou Ajay K. Dalai Nicolas Abatzoglou 《Fuel Processing Technology》2009
An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H2/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C5+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C5+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation. 相似文献
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Band structure calculations were performed for tungsten nitride, cobalt tungsten nitrides, and platinum slabs. The major requirements for the development of a superior cathode catalyst are: (1) that the Fermi level of the cathode catalyst is close to the energy level of the lowest unoccupied molecular orbital of O2, the lowest unoccupied atomic orbital of an oxygen atom, and the lowest unoccupied atomic orbital of a hydrogen atom so that they can readily interact with one another; and (2) that the cathode catalysts have smaller ΔE value which represent the difference between the Fermi level and the peak position of the density of states of the O_p orbital of O2 adsorbed on the catalyst. The active site structures of cobalt tungsten nitrides for activation of the oxygen reduction reaction were found to have the surface structure of Co–O–Co, which lowered the unoccupied orbital of the oxygen atom to approximately that of the Fermi level. However, this structure concomitantly lowered the Fermi level, which resulted in an increase in ΔE. Consequently, the optimal cathode catalyst regarding the surface conformation contains a Co–O–Co structure that is dispersed on the surface of the cobalt tungsten nitride. The cobalt tungsten oxynitride exhibited a catalytic activity for the oxygen reduction reaction. A linear dependence is observed between the ΔE and the oxygen reduction reaction offset potentials of the tungsten nitride, cobalt tungsten nitride, cobalt tungsten oxynitride, and platinum. 相似文献
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采用电弧等离子体技术,以铁粉、镍粉或La-Ni混合物为催化剂,由中国煤成功地制备出单壁纳米炭管.综合运用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能量散射探针(EDX)及激光拉曼光谱等技术对所制得的单壁纳米炭管进行分析表征,发现得到的单壁纳米炭管具有较高的纯度;所制得的煤基单壁纳米炭管的直径与所使用的催化剂有关,以铁粉为催化剂时,单壁炭管的直径处于1.2~2.2nm之间,而以镍粉或La-Ni混合物为催化剂时得到单壁炭管的直径相近,处于1.26~1.50nm之间;与单壁炭管伴生的其他杂质是少量的碳包纳米金属颗粒和微量的源于原料煤中矿物质的Al、Si等杂原子. 相似文献
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Bas M. Vogelaar A. Dick van Langeveld Patricia J. Kooyman C. Martin Lok Raimond L.C. Bonn Jacob A. Moulijn 《Catalysis Today》2011,163(1):353
The formation of nickel and cobalt nanoparticles in hydrogenation catalysts and their stability against sintering during the reduction of the oxidic precursors were investigated. The morphology of the catalysts was manipulated by varying the reduction conditions. The catalysts were characterized using temperature programmed reduction (TPR), hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HREM). The transformation of the oxidic precursor into the active phase was monitored using quasi in situ HREM, which proved to be an excellent technique to visualize the formation of metal nanoparticles. For the nickel catalyst the reduction temperature plays a crucial role, whereas time is more critical for the cobalt catalyst. The sintering rate of cobalt is considerably lower than that of nickel during reduction. It is concluded that the activation energy for sintering is significantly higher for nickel than for cobalt. A model is proposed which depicts the structure of both types of catalysts in their oxidic and reduced state. TPR and XPS results indicate that the passivated catalysts contain approximately two oxygen atoms per surface Ni or Co atom. 相似文献
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《Applied catalysis》1990,57(1):223-240
The effect of fluorine incorporation on alumina support on the surface structure of unpromoted molybdenum, promoted cobalt—molybdenum and nickel—molybdenum catalysts, and their activity for hydrogenation of cyclohexene has been studied. The incorporation of 0.2 and 0.8 wt.-% fluorine on the alumina was carried out by impregnation with NH4F solutions. The catalysts in the oxidic state were characterized by X-ray diffraction and ammonia adsorption and in the sulfide state by X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR) of adsorbed NO. The absence of significant changes in the binding energy values of Mo3d and Ni2p (or Co2p) levels in the XPS spectra of the fluorine-containing catalysts as compared to the fluorine-free counterpart does not support the existence of an electronic effect of fluorine. The quantitative XPS results showed, however, that fluorine clearly increases the dispersion of molybdenum and promoter, this being linearly correlated to surface fluorine content. The IR results of adsorbed NO also indicate that fluorine incorporation leads generally to minor sizes of MoS2 slabs, and more exposed promoter atoms, except for the cobalt in the CoMo/F(0.2)A catalyst. It is suggested that the increase in the dispersion of the supported active phase is a secondary effect of fluorine incorporation, which may result from the observed textural changes of the alumina and its small partial solubilization provoked by NH4F solution. It was found that the incorporation of fluorine enhances appreciably, moderately and considerably the hydrogenation activity of molybdenum, cobalt—molybdenum an nickel—molybdenum catalysts, respectively. Such increase in hydrogenation activity is not directly correlated to the exposed atoms probed by NO adsorption, and is only loosely related to molybdenum dispersion for the molybdenum and cobalt—molybdenum catalysts. The lack of similar reliable correlations for the nickel—molybdenum catalysts suggests that other structural parameters such as extent of reduction-sulfidation and certain configurations of molybdenum ions and sulfur vacancies may govern hydrogenation activity. 相似文献
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以高比表面积和规整性强的蜂窝陶瓷(2MgO2·Al2O3·SiO2)为载体,涂敷TiO2后,用水热合成法分别负载铁、钴和镍盐,500 ℃焙烧及硼氢化钾(KBH4)浸渍后,合成了负载型金属催化剂。负载不同金属盐的催化剂析氢性能比较结果为钴>铁>镍。实验研究表明,负载硝酸铁[Fe(NO3)3·9H2O]和氯化钴(CoCl2·6H2O)的催化剂经KHB4浸渍后析氢性能均明显改善。利用X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的表征结果证实,负载硝酸铁催化剂表面真正起催化析氢性能的活性组分为单质铁,负载氯化钴催化剂表面生成了CoTiO3,且该催化剂具有优良的催化碱性KBH4溶液水解析氢性能,常温下该催化剂0.34 g于NaOH质量分数约为18%,KBH4质量分数约为10%的溶液中催化析氢速率可达160 mL·min-1。 相似文献
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In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe
matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of states (DOS) of the systems. In contrast to the ab initio methods, the latter allows studying nanostructures with diameters comparable to the real ones. The calculations show that
both kinds of inclusions lead to changes of the DOS of the carriers near the Fermi level, which may affect optical, electrical
and thermoelectric properties of the material. These changes depend on the size, shape, and concentration of inclusions. 相似文献
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《Diamond and Related Materials》2000,9(3-6):728-731
In this work, we investigated different hydrogenated amorphous carbon (a-C:H) films grown by radio frequency (RF) magnetron sputtering covering a large variety of films from polymer-like carbon (PLC) to diamond-like carbon (DLC). Photothermal deflection spectroscopy (PDS), transmission spectroscopy in the visible and near infrared (IR) region were combined with electron spin resonance (ESR) measurements. The optical absorption spectra were analysed assuming a distribution of two overlapping Gaussian bands near the Fermi level in order to deduce the density of states (DOS) at the Fermi level. From the DOS and the density of paramagnetic states a correlation energy for midgap states is derived. 相似文献
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The nickel on active carbon (Ni/A.C.) catalysts prepared by a simple chemical vapor deposition (CVD) method showed comparable catalytic activities for the vapor phase carbonylation of methanol to those of the catalysts prepared by impregnating A.C. with nickel nitrate and activating by hydrogen treatment. The CVD method was successfully applied to the in situ catalyst preparation. 相似文献
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Thani Jermwongratanachai Gary Jacobs Wilson D. Shafer Wenping Ma Venkat Ramana Rao Pendyala Burtron H. Davis Boonyarach Kitiyanan Syed Khalid Donald C. Cronauer A. Jeremy Kropf Christopher L. Marshall 《Topics in Catalysis》2014,57(6-9):479-490
Freshly H2-reduced catalyst samples and FTS catalyst samples (i.e., freshly reduced and immediately exposed to the onset of FTS conditions corresponding to 50 % CO conversion) were prepared. Each sample was coated in situ using molten polywax and solidified so that an air-protected sample was obtained, which was stored in inert gas. XAS was utilized to investigate the oxidation state of cobalt. A fraction of cobalt crystallites in the freshly reduced research catalysts having lower-than-commercial loading and smaller crystallites undergoes a degree of oxidation to CoO at the onset of FTS conditions simulating 50 % CO conversion (i.e., the H2O partial pressure is high enough to induce some oxidation). Therefore, by decreasing Co content with the aim of improving the dispersion of cobalt and Co efficiency, very small Co crystallites are obtained. Their reoxidation at the onset of FTS is an unintended consequence. Thus, catalysts should be designed to have an optimum narrow cluster size range—small enough to increase Co surface site densities, but large enough to avoid reoxidation, and the stability problems that arise from having unreduced Co in the working catalyst (e.g., a complex coalescence and reduction mechanism). 相似文献
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Steam reforming of methane, kerosene and heavy oil over a nickel/alumina commercial catalyst and other materials such as limestone,
dolomite and iron ore, was studied using a 5 cm i.d. fluidized bed reactor. The effects of operating parameters on conversion,
hydrogen yield, product gas composition and elutriation of fine catalysts were investigated. It was found that a fluidized
bed is flexible enough to handle various feedstocks, including hydrocarbons heavier than naphtha, because it permits the addition
of catalyst to, or withdrawals of, coked catalyst from the bed. The yield of hydrogen obtained from fluidized bed steam reforming
of heavy oil at 800‡C over limestone was similar to that obtained over commercial nickel-based catalyst. This indicates that
limestone could be a promising catalyst for the production of hydrogen from heavy oil. However, hydrogen yield decreased with
reaction time in the experiments using the limestone catalyst. The main cause of the decrease in hydrogen yield was elutriation
of fine catalysts from the bed during the reaction. 相似文献
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Mark R. Hatswell W.Roy Jackson Francis P. Larkins Marc Marshall Douglas Rash Donald E. Rogers 《Fuel》1983,62(3):336-341
Some of the inherent cations of Victorian brown coals have been exchanged for iron by treatment with solutions of iron salts. Coals with various iron contents are obtained by variation of the pH of the solutions used. Hydrogenation of coals treated in this way at 395 °C, and an initial hydrogen pressure of 10 MPa, give product yields similar to those obtained using commercial cobalt molybdate on alumina catalysts, and greater than those obtained using red mud as a catalyst. The increase in yields compared with non-catalysed experiments results mainly from increased production of asphaltenes. The amount and composition of gas (80–90 wt% C02, resulting from decarboxylation) remains constant. Despite the similar conversions, the hydrogen consumption and tetralin/naphthalene ratios for iron-catalysed experiments are less than for cobalt—molybdate-catalysed experiments. 相似文献
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A. M. Gyul’maliev A. S. Maloletnev M. Ya. Shpirt L. A. Zekel’ M. A. Gyul’malieva 《Solid Fuel Chemistry》2009,43(5):295-301
The thermodynamic and quantum-chemical aspects of hydrogenation of coal organic matter in the presence of iron and nickel
compounds as catalysts were considered. A thermodynamic analysis of the formation reaction of catalytically active catalyst
entities under hydrogenation conditions was performed. The electronic structure of FeO, FeS, FeS2, NiO, and NiS with the minimal number of iron and nickel atoms and their activated complexes with an H2 molecule were calculated by the ab initio Hartree-Fock method using the STO 6-311G basis set. A comparative catalytic activity
of transition states of this kind was evaluated. 相似文献
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Activity of cobalt and iron catalysts in ammonia synthesis was determined under a pressure of 10 MPa and at the temperature range of 673–823 K, in a six-channel integral steel reactor. The catalytic ammonia decomposition was studied in a differential reactor under the atmosphere of low concentration of ammonia (<6%) in the temperature range of 673–823 K under atmospheric pressure. The determined values of the activation energy for the ammonia synthesis reaction over cobalt and iron catalysts are 268 and 180 kJ/mol, respectively, whilst for the ammonia decomposition reaction they are equal to 111 and 138 kJ/mol. The cobalt catalyst showed lower activity than a commercial iron catalyst in ammonia synthesis reaction. The cobalt catalyst turned out to be more effective in ammonia decomposition reaction than the iron one. 相似文献