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11.
以正硅酸乙酯(TEOS)为硅源,十六烷基三甲基溴化铵(CTAB)为表面活性剂,仲钨酸铵为钨源,采用水热晶化法一步合成了不同钨含量(以Si、W物质的量比nSi/nW表示)的WO3-MCM-48,然后经甲烷/氢气(V/V=1/4)混和气体程序升温还原碳化(TPC),制备出了WxC-MCM-48(x=1、2)催化剂,采用XRD、N2吸附-脱附和NH3-TPD对样品的结构进行了表征,用噻吩作为模型化合物,对WxC-MCM-48催化剂的加氢脱硫催化活性进行了评价。结果表明,在一定钨含量的条件下,WO3-MCM-48和WxC-MCM-48样品仍然保持MCM-48的三维立方有序介孔结构,nSi/nW=30~15时,碳化钨的物相为W2C;nSi/nW=7.5时,碳化钨为W2C和WC物相,WxC-MCM-48催化剂表现出了良好的加氢脱硫催化性能。 相似文献
12.
One of the major techniques used for the method development of ternary and quaternary high performance liquid chromatography (HPLC) systems has been to use mixture designs, often referred to as "Glajch's Triangle". This technique does not allow for the systematic and simultaneous optimization of other factors such as gradient time, pH and temperature that affect the quality of separations. An alternative approach is to use experimental designs. The condition, however, that the composition of all components of the mobile phase must total 100% presents a problem when trying to mathematically represent ranges of each mobile phase constituent of a ternary or quaternary system. A method is described here, based on spherical coordinate representations, that adheres to the constraints of the mobile phase composition and allows experimental designs, such as central composite and factorial designs, to be applied to the simultaneous optimization of the mobile phase composition. Other factors, in particular temperature and gradient time, can then be included in the design. As a result of applying these designs to the HPLC separation of phenols and corticosteroids, it was found necessary to include three-way interactions between experimental factors in the model. The significance of these interactions shows that they need to be considered in HPLC method development. 相似文献
13.
Ternary Lithium Rare Earth Nitrates with Lonesome Nitrate Ions: Li3[M(NO3)5](NO3) (M = Gd? Lu, Y). The Crystal Structure of Li3Er(NO3)6 Single crystals of the ternary nitrate Li3Er(NO3)6 are obtained from a solution of “Er(NO3)3” in the melt of LiNO3. In Li3Er(NO3)6 (monoclinic, P21/n, Z = 4; a = 776.0(1); b = 748.86(8); c = 2 396(1) pm; β = 90.76(3)°; R1 = 0.0490; wR2 = 0.0792), Er3+ is surrounded by five bidentate nitrate ligands yielding the anionic units [Er(NO3)5]2?. These are arranged in the direction of the 21 screw axis. Two lonesome NO3? ions are in the middle of such a “helix” and are connected by Li+ with the anions [Er(NO3)5]2?. The helices are moved against each other by about half of the lattice constant a and are connected by further Li+ ions. 相似文献
14.
S Katrych A Grytsiv A Bondar T Velikanova M Bohn 《Journal of solid state chemistry》2004,177(2):493-497
Phase equilibria in the Nb-Nb5Si3-NbB region were studied in the melting (crystallization) range by means of light microscopy, XRD, SEM and EMPA on alloys after arc-melting and annealing at 1800°C and at subsolidus temperatures. Phase transition and melting temperatures were determined by DTA and pyrometric Pirani-Alterthum technique resulting in a solidus projection and two isopleths, Nb77Si23-Nb77B23 and Nb99Si1-Nb5Si2B. The T2-phase Nb5Si3−xBx (0?x?2, Cr5B3-type) was found to form equilibria with (Nb), NbB, Nb3Si, and with the T1-phase (Mn5Si3 derivative type). The T2-phase melts incongruently (Nb5Si1.8B1.2 at 2245°C) and forms a quasibinary eutectic with the niobium solid solution on a minimum tie-line at ∼1880°C. 相似文献
15.
16.
Preparation and Crystal Structure of Rb2Ni3Se4 The compound Rb2Ni3Se4 was synthesized by heating a mixture of rubidium carbonate, nickel and selenium at 850°C in an atmosphere of hydrogen. The compound has a golden lustre and crystallizes with the K2Pd3S4-type structure; a = 10.555(3) Å, b = 27.588(6) Å, c = 6.031(6) Å, Z = 8, Fddd (No. 70). The structure can be described as a stacking of layers of the composition Rb2Ni3Se4 with a stacking sequence abcd. The electrostatic part of lattice energy (MAPLE) will be discussed for compounds of the compositions A2M3X4 (A K, Rb, Cs; M Ni, Pd, Pt and X S, Se). 相似文献
17.
M. Rapposch E. Kostiner S. F. Wayne H. Nowotny 《Monatshefte für Chemie / Chemical Monthly》1985,116(11):1237-1245
The crystal structure of molybdenum cementite Mo12Fe22C10 (-phase) has been determined by means of a single crystal x-ray diffraction study of crystal fragments. The lattice parameters were found to be:a=10.865 (3),b=7.767 (2),c=6.559 (2) Å and =120.13 (2)°, space group C2/m;Z=1. From the analysis ofPatterson maps and differenceFourier analysis the atomic parameters were derived, yielding a residual ofR=0.059. The crystal structure contains octahedral and triangular prismatic groups which accommodate the carbon atoms in their voids, as is usually found in interstitial compounds. The octahedral building group consists of four Mo- and two Fe-atoms, the triangular prism is built up by four Fe-and two Mo-atoms. The mode of filling of the metal polyhedra is discussed.
Die Kristallstruktur von Molybdän-Zementit, Mo12Fe22C10 (-Phase)
Zusammenfassung Die Kristallstruktur von Molybdän-Zementit, Mo12Fe22C10 (-Phase) wird auf Grund von Einkristall-Beugungsaufnahmen unter Anwendung vonPatterson-and DifferentialFourier-Analysen bestimmt. In der monoklinen Elementarzelle (a=1.870;b=7.67;c=6.563 Å, =120.1°) Raumgruppe C 2/m befindet sich eine Formeleinheit Mo12Fe22C10 (oderZ=2, Mo6Fe11C5). DerR-Wert von 6% für 1200 Reflexe unterstreicht die Richtigkeit der Struktur, die aus oktaedrischen und trigonal prismatischen Gruppen aufgebaut ist. Die Oktaedergruppe besteht aus 4 Mo- und 2-Fe-Atomen, die trigonal prismatische Gruppe aus 4 Fe- und 2 Mo-Atomen. Die Kohlenstoffatome füllen die Lücken dieser Bauelemente, wie es für typische Einlagerungscarbide (Komplexcarbide) erwartet werden kann.相似文献
18.
《Surface and interface analysis : SIA》2003,35(10):835-841
We have examined the optimal interface structure, ideal work of adhesion and bonding character of polar Ti(110)/TiN(111) interfaces by first‐principles density‐functional plane‐wave pseudopotential calculations. Both Ti‐ and N‐terminated interfaces, including six different interface structures, were calculated. The interface structure for each termination, continuing the TiN crystal structure across the interface, has the largest work of adhesion. Although both terminations yield substantial adhesion energies in the range 3–7 J m?2, the N‐terminated interface is ~4 J m?2 stronger than the Ti‐terminated interface. Analysis of the interfacial electronic structure shows that the Ti‐terminated interface is a mixed strong, metallic and weak covalent character, whereas the N‐terminated interface is a polar covalent bond similar to the Ti/TiC interface. Further study of the separation of the optimal interface shows that the cleavages will never fracture at the interface due to the strong bonding, which is consistent with the experimental results. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
20.
T. Kowalska 《Chromatographia》1990,29(7-8):389-394
Summary In our previous publication we have introduced a new model of solute retention in RP-HPLC systems with ternary mobile phases of the B+AB1+AB2 type (B: acetonitrile or tetrahydrofuran; AB1: methanol; AB2: water). That model proposed no stoichiometric differentiation between acetonitrile and tetrahydrofuran, alternatively present in the solvent system; moreover, it made some very rough assumptions only as to the intermolecular interactions among the mobile phase constituents.This paper introduces a significant refinement to the already established retention model, which is based on the simple quantitative relationships between acetonitrile and tetrahydrofuran, and the remaining components of the ternary liquid system. The refined model is tested with same experimental data. 相似文献