共查询到20条相似文献,搜索用时 31 毫秒
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Shengguang Wang Burcin Temel Juan Shen Glenn Jones Lars C. Grabow Felix Studt Thomas Bligaard Frank Abild-Pedersen Claus H. Christensen Jens K. Nørskov 《Catalysis Letters》2011,141(3):370-373
Abstract
It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals. 相似文献2.
Nobuhiro Iwasa Tomoyuki Mayanagi Noriaki Ogawa Kentaro Sakata Nobutsune Takezawa 《Catalysis Letters》1998,54(3):119-123
Pd and Pt supported on ZnO, Ga2O3 and In2O3 exhibit high catalytic performance for the steam reforming of methanol, CH3OH+H2OCO2+3HH2, and the dehydrogenation of methanol to HCOOCH3, 2CH3OHHCOOCH3+2HH2. Combined results with temperature-programmed reduction (TPR) and XRD method revealed that Pd–Zn, Pd–Ga, Pd–In, Pt–Zn, Pt–Ga and Pt–In alloys were produced upon reduction. Over the catalysts having the alloy phase, the reactions proceeded selectively, whereas the catalysts having metallic phase exhibited poor selectivities. 相似文献
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E. Valova S. Armyanov A. Franquet A. Hubin O. Steenhaut J-L. Delplancke J. Vereecken 《Journal of Applied Electrochemistry》2001,31(12):1367-1372
Coatings of electroless Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys were plated in alkaline citrate baths containing amino alcohols, but not free ammonia ions. The reference Ni–P alloy was used as an intermediate layer in the sandwich: Ni–Me–P/Ni–P/substrate. An extremely homogeneous thickness distribution of all alloy components was found by applying scanning Auger electron spectroscopy (SAES(. The inclusion of refractory metals at the expense of nickel and without substantial change in phosphorus content was established. A non-oxidized state of the codeposited Re and W in Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys was determined by means of X-ray photoelectron spectroscopy examination, as well as by SAES profiles, revealing the absence of oxygen throughout the coatings. All alloy films are amorphous and paramagnetic. 相似文献
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Gheorghiţa Mitran Adriana Urda Nathalie Tanchoux François Fajula Ioan-Cezar Marcu 《Catalysis Letters》2009,131(1-2):250-257
Ln–Mg–Al mixed oxide catalysts (Ln = Ce, Sm, Dy, Yb) were prepared from layered double hydroxide precursors, characterized using XRD, N2 adsorption, TG-DTG, EDX, H2-TPR and CO2-TPD techniques and tested in the oxidative dehydrogenation of propane in the temperature range 450–600 °C. For all the catalysts the conversion increases with increasing the reaction temperature while the propene selectivity decreases to the benefit of carbon oxides for Ce-based system and of cracking products for the others. The best yields in propene were obtained with Dy- and Sm–Mg–Al–O catalysts. No correlation between the reducibility of the rare-earth cation and the catalytic performances was observed. A linear correlation between the catalyst basicity and the propene selectivity was evidenced. 相似文献
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Nutthavich Thouchprasitchai Apanee Luengnaruemitchai Sangobtip Pongstabodee 《Journal of Industrial and Engineering Chemistry》2013,19(5):1483-1492
Water-gas shift reaction was investigated over Cu–Zn, Cu–Fe and Cu–Zn–Fe composite-oxide catalysts at atmospheric pressure from 200 to 375 °C in terms of reducing the CO content with maximal H2 yield. The Cu0.15ZnFe2 spinel catalyst expressed a higher CO conversion level and H2 yield at a lower temperature compared to the Cu0.15Zn and Cu0.15Fe catalysts. Adding H2O to the feed up to 30% (v/v), but not above, increased the CO reduction level, presumably by increasing the hydroxyl species to react with the adsorbed CO. Increasing the W/F ratio to 0.24 g s cm?3 increased the CO conversion level to 0.76 at 275 °C with the Cu0.15ZnFe2 catalyst, and could be further increased to 0.86 at 350 °C by increasing the Cu molar ratio to 0.30 (Cu0.30ZnFe2). Nevertheless, increasing the Cu molar content to 0.50 reduced the CO conversion level. No requirement for adding O2 when using the Cu0.30ZnFe2 catalyst at >260 °C was observed. Increasing the CO content in the reactant decreased its conversion level. The performance of the Cu0.30ZnFe2 catalyst was stable over a test period in a CO-rich condition. No undesired product was detected, suggesting a higher selectivity for hydrogen production with a low CO content. 相似文献
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Zhuoqi Tang David Furniss Nigel C. Neate Trevor M. Benson Angela B. Seddon 《Journal of the American Ceramic Society》2019,102(1):195-206
A systematic investigation is presented, for the first time, of a 1000 ppmw (parts per million, by weight) Dy3+-doped Ge–As–Ga–Se chalcogenide glass series, with a fixed low Ga content of 1 atomic% (at. %), suitable for active mid-infrared fiber optics. Seven glasses constitute the series, which have increasing average coordination number from 2.49 to 2.61, in steps of 0.02, with the GeSe2, As2Se3, and Ga2Se3 stoichiometries kept. Glass formation is confirmed using X-ray diffraction and differential scanning calorimetry. Fourier transform infrared spectroscopy is reported for the series. Parallel plate viscometry enables prediction of fiber-drawing temperatures and, with differential thermal analysis, determines the potential for fiber fabrication. X-ray diffraction of samples after parallel-plate viscometry shows that Ge25As9Ga1Se65 (at. %) alone, in the glass-series, devitrifies to form the single-crystalline phase: monoclinic-GeSe2; scanning electron microscope imaging suggests that this phase is both surface and bulk grown. Overall, the recommended host glass at. % compositions for doping with rare-earth ions and drawing to active mid-infrared fiber are: Ge17.5As18Ga1Se63.5, Ge15As21Ga1Se63, and Ge12.5As24Ga1Se62.5. 相似文献
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H. A. El Shayeb F. M. Abd El Wahab S. Zein El Abedin 《Journal of Applied Electrochemistry》1999,29(4):473-480
The electrochemical behaviour of pure aluminium and three of its alloys were investigated in 0.6m NaCl in the presence and absence of In3+ ions. The study comprised polarization and potentiostatic current–time measurements complemented by SEM–EDAX investigation. In 0.6m NaCl the corrosion resistance of the alloys decreases in the following order: Al < Al–Sn < Al–ZnAl–Zn–Sn. The addition of In3+ ions to the test electrolyte revealed activation of pure Al which increases with increase of In3+ concentration. Similar results were obtained for the binary Al–Zn and the ternary Al–Zn–Sn alloys, while Al–Zn alloy displayed a higher activation effect with In3+. It is also concluded that the existence of Zn either as an alloying element or present as a cation in the electrolyte leads to an enhanced activity of aluminium in presence of In3+ ions. Deactivation is observed in the case of Al–Sn alloy on addition of In3+ because tin retards the diffusion pathway of In to the bulk alloy, in addition to the presence of iron as an impurity in the alloy. 相似文献
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A series of SiO2–TiO2 mixed oxides was prepared by the sol–gel route, and the influence of several important preparation parameters (Ti precursors, content, and calcination temperature) on the Si–O–Ti connectivity, coordination of titanium and surface acidity has been studied using various analytical techniques. The solids obtained were largely amorphous and characterized by Ti enrichment on surfaces with low titanium content; however, the addition of titanium greater than 50 mol% into the SiO2 matrix led to significant phase separation of crystalline anatase. The Ti atoms are tetrahedrally coordinated with Si/Ti ratios higher than 10 and gradually enter into octahedral positions in the silica matrix with further increase in the titanium content. High-temperature treatment can break Si–O–Ti linkages and eliminate hydroxyl groups, resulting in a decrease in acid site density. 相似文献
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《Journal of Adhesion Science and Technology》2013,27(8-9):1141-1156
Abstract The wetting of alumina substrates by Fe–Ti, Fe–P and Fe–Ti–P alloys has been investigated using sessile drop experiments conducted under an inert gas atmosphere in the temperature range of 1550 to 1620°C. The surface and interfacial structures have been explored by scanning electron microscopy and energy dispersive X-ray spectroscopy. Substantial additions of titanium are known to induce steel melts to wet alumina due to the formation of a Ti-rich reaction product at the alloy/ceramic interface, but the present work has shown that even low Ti concentrations can induce a reactive wetting process leading to an improvement of the wettability of alumina by Fe alloys. The contact angle of molten steel containing phosphorus on alumina decreased with increasing P content. The improvement of the wetting behaviour in this system was attributed solely to the adsorption of P onto the surface of the Fe melt. The addition of P as a ternary alloying element to the system Fe–Ti proved to be beneficial to the wetting behaviour. The measured contact angles were much lower than those in the binary systems Fe–Ti and Fe–P. This effect was related to the fact that P enhances the activity of Ti in the Fe melt. According to experimental observations, it turns out that the wettability of liquid Fe-based alloys, when an Al2O3 surface is present, is not only a property of the metal/oxide couple but is also dependent on the oxygen partial pressure, whereas temperature variations bring about a comparatively small effect. This work is of interest in understanding the phenomena pertaining to inclusion engineering and steel– refractory interactions, such as the clogging of submerged entry nozzles by agglomerated alumina particles during the continuous casting process. 相似文献
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《Diamond and Related Materials》1999,8(10):1838-1846
This paper summarizes theoretical and experimental studies of cBN–TiN and cBN–TiC of cBN:TiN/TiC molar ratio 1:1 and 2:1. Theoretical calculations show that, at temperatures between 1000 and 1400°C, TiN reacts with BN forming one new phase, TiB2, and that TiC reacts with cBN forming two new phases, TiB2 and TiC0.8N0.2.. Experimental cBN–TiC/TiN composites were prepared by high pressure hot pressing and the samples were subsequently heat treated.After heat treatment, sinters of cBN–TiN/TiC were characterized using transmission electron microscopy and X-ray diffraction. The samples exhibited a dense polycrystalline structure, and a thin layer of fine TiB2 was visible at the BN–binder interface. It was found that hardness decreased significantly after heat treatment. 相似文献
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