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101.
Nicholas Kob Russell S. Drago Vaneica Young John Osegovic 《Reaction Kinetics and Catalysis Letters》1999,66(2):205-210
The regeneration of solid acid catalysts used in alkylation was studied using cal-ad. It was found that an acid site strength
of −ΔH=32 kcal/mol is needed to catalyze the reaction. 相似文献
102.
Jianghua Zeng Dingsheng Yuan Yingliang Liu Jingxing Chen Sanxiang Tan 《Frontiers of Chemistry in China》2009,4(2):127-131
Tungsten carbide (WC) nanocrystals have been prepared by a solvothermal method with Mg as the reductant and WO3 and anhydrous ethanol as the precursors. The effects of time and temperature on the synthesis of WC were investigated and
a probable formation mechanism was discussed. The obtained WC nanocrystals were characterized by X-ray diffraction, transmission
electron microscopy, energy dispersive spectroscopy and electrochemical methods. Hexagonal closepacked WC was successfully
synthesized when the temperature was as low as 500°C. The content of carbon was more than that of W, indicating that the composition
of the treated sample was C and WC only. The diameters of WC nanocrystals were ranged from 40 nm to 70 nm and the nanocrystals
were dispersed on carbon films. The electrochemical measurements reveal that WC nanocrystals obviously promote Pt/C electrocatalytic
ability for the oxygen reduction reaction.
__________
Translated from Chinese Journal of Catalysis, 2008, 29(7) (in Chinese) 相似文献
103.
Monomeric tungsten oxo‐aminoalkoxides W(O)(OPri)3(L) [L = O(CH2)nNMe2; n = 2 (dmae, 1) and 3 (dmap, 2 )] were synthesized by alcohol exchange with [W(O)(OPri)4]2 and characterized spectroscopically. 1, 2 and [W(O)(OPri)4]2 were used as precursors for the aerosol‐assisted chemical vapour deposition of WO3 thin films, which were characterized by glancing angle X‐ray diffraction, SEM and transmission‐reflectance measurements. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
104.
105.
Aldol‐type condensation reactions of a number of cyclic, acyclic and substituted cyclic ketones were investigated using the W(CO)6/CCl4/UV system. The progress of the reactions was followed by IR and GC‐MS techniques. The cyclic ketone derivatives with β‐ and γ‐substituent gave the expected condensation products. However, the α‐substituted cyclic, acyclic and unsubstituted cyclic ketones with rings larger than six did not. Formation of [W]–ketone complexes with all of the ketones used was observed by FTIR. With respect to our studies, a mechanism involving an intermediate seven‐coordinate tungsten complex has been proposed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
106.
Frank Langhans Stefan Kiefer Carsten Hartmann Toni Markurt Tobias Schulz Christo Guguschev Martin Naumann Sandro Kollowa Andrea Dittmar Jürgen Wollweber Matthias Bickermann 《Crystal Research and Technology》2016,51(2):129-136
In order to evaluate the possible involvement of crucible materials in the growth of AlN bulk crystals grown by physical vapor transport, we applied growth conditions with a high vertical thermal gradient and hence high supersaturation of aluminum vapor. Under these conditions, precipitates formed causing diffuse grayish substructures at the initial growth interface and in the crystal body, decorating dislocations. Electron microscopy studies revealed that the precipitates are elongated, single‐phase particles with sizes of 50–500 nm of commensurate structure, oriented along the <110> direction. Chemical analysis of the precipitates showed tungsten as well as carbon and oxygen. The lattice parameters of the precipitates are in close agreement to hexagonal tungsten hemicarbide (W2C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W2C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients. 相似文献
107.
Using density functional theory methods, we have studied carbon trioxide, its adsorption and dissociation on Ag(100). In the gas phase, two isomers are found, D3h and C2v, with the latter of 2.0 kcal mol?1 lower in energy at the PW91PW91/6?31G(d) level. For CO3 on Ag(100), the calculated adsorption energy is 91.2 and 89.1 kcal mol?1 for the bi‐coord perpendicular and tri‐coord parallel structures, respectively. Upon the adsorption, 0.50 ~ 0.56 electron is transferred from silver to CO3, indicative of significant ionic characters of the adsorbate‐surface bonding. In addition, the geometry of CO3 is largely changed by its strong interaction with silver. For CO3(ad) → O(ad) + CO2(gas), the energy barrier is calculated to be 19.8 kcal mol?1 through the bi‐coord path. The process is endothermic with an enthalpy change of +17.3 ~ +26.7 kcal mol?1 and the weakly chemisorbed CO2 is identified as an intermediate on the potential energy surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
108.
T. A. Dang H.‐J. Lunk S. Roychowdhury T. A. Frisk T. J. Bard 《Surface and interface analysis : SIA》2010,42(1):45-51
Solid standards prepared by freeze‐drying consistently showed a high degree of homogeneity. The freezing process, completed in fractions of a second, preserves the original homogeneous distribution of the dopants, and the subsequent sublimation step would minimize any disturbance. Compared to those prepared by conventional methods such as blending and spiking, freeze‐dried standards exhibited superior lateral distribution and better uniform depth distribution. There is, however, a concentration constraint for achieving homogeneity. At 5% doping, segregation was observed in both lateral and depth distribution. Many tungsten standards doped with 10–28 elements ranging from 10 to 200 ppm were successfully prepared and used as controls for a number of analytical techniques including glow discharge mass spectrometry (GDMS) and d.c.‐arc optical emission spectroscopy (OES). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
109.
Emma E. McCabe 《Journal of solid state chemistry》2010,183(3):624-143
The new phases Ba2LaMNb4O15: M=Mn, Fe were prepared by solid state reaction at 1100 °C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90±15 over the range 10-320 K. Ba2LaFeNb4O15 is highly insulating with bulk conductivity ?10−8 ohm−1 cm−1 at 25 °C and tan δ?0.001 over the range 100-320 K and at 105 Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba2LaTi2Nb3O15 show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti4+ by a mixture of (Mn, Fe)3+ and Nb5+. 相似文献
110.