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141.
142.
Dispersion state and catalytic properties of vanadia species on the surface of V_2O_5/TiO_2 catalysts 总被引:1,自引:0,他引:1
The dispersion state and catalytic properties of anatase-supported vanadia species are studied by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), H2 temperature-programmed reduction (TPR) and the selective oxidation of o-xylene to phthalic anhydride. The almost identical values of the experimental dispersion capacity of V2O5 on anatase and the surface vacant sites available on the preferentially exposed (001) plane of anatase suggest that the highly dispersed vanadium cations are bonded to the vacant sites on the surface of anatase as derived by the incorporation model. When the loading amount of V2O5 is far below its dispersion capacity, the dispersed vanadia species might mainly consist of isolated VOx species bridging to the surface through V-O-Ti bonds. With the increase of V2O5 loading the isolated vanadia species interact with their nearest neighbors (either isolated or polymerized vanadia) through bridging V-O-V at the expenses of V-O-Ti bonds, resulting in the increase of the ra 相似文献
143.
用直径7 μm的碳纤维组合成超微圆盘电极,以聚苯胺修饰电级.以阶梯扫描法、循环伏安法、双阶跃计时电量法和交流阻抗法等,研究了Cd2+在该电极上的表面络合吸附特性和电极过程.在循环伏安图上出现两个还原峰,实验和理论都证明,由于电极表面的聚苯胺对Cd2+的特性吸附,形成电活性的表面吸附态络合物.因此,这种表面络合物首先被还原,形成峰电位-0.90 V处的表面络合吸附波,还原峰电位比Cd2+直接还原电位(-0.98 V)正移,循环反扫时,氧化波无峰形.根据实验数据推测了电极过程的反应机理,证实该还原波具有扩散和表面反应同时控制的表面络合吸附波的特性.理论计算与实验基本一致,并求得了表面吸附态配合物的形成常数、吸附量和表面络合反应的动力学参数.实验还证实,在峰电位-1.06 V 处的还原波,是Cd2+的表面吸附还原态诱导而产生的催化氢波. 相似文献
144.
145.
The macroradical decay in poly(methyl methacrylate) samples with different thermal histories was investigated in the temperature interval 20–100 °C using ESR spectroscopy and the second order kinetic model. The rate constants exhibit two different regimes with the transitions atT
tr=68±1°C which are independent of thermal treatment. ForT<T
tr andT>T
tr the rate constants as well as the corresponding activation parameters are sensitive to history because of different physical microstructures. The compensation law, i.e., the linear relation between lnk
o, eff andE
eff, was analyzed in terms of the so-called compensation quantitiesk
c andT
c and a proximity betweenT
c=T
tr andT
o=53±3 °C — Vogel temperature for -segmental dynamics was found. A comparison of kinetic and dynamic data suggests that the decay of terminal macroradicals in the low-temperature region is controlled by secondary relaxations and that the -mobility contributes to a more rapid decay at higher temperatures belowT
g. 相似文献
146.
For every integrable allocation (X
1,X
2, ...,X
n
) of a random endowmentY=
i
=1/n
X
i
amongn agents, there is another allocation (X
1*,X
2*, ...,X
n
*) such that for every 1in,X
i
* is a nondecreasing function ofY (or, (X
1*,X
2*, ...,X
n
*) areco-monotone) andX
i
* dominatesX
i
by Second Degree Dominance.If (X
1*,X
2*, ...,X
n
*) is a co-monotone allocation ofY=
i
=1/n
X
i
*, then for every 1in, Y is more dispersed thanX
i
* in the sense of the Bickel and Lehmann stochastic order.To illustrate the potential use of this concept in economics, consider insurance markets. It follows that unless the uninsured position is Bickel and Lehmann more dispersed than the insured position, the existing contract can be improved so as to raise the expected utility of both parties, regardless of their (concave) utility functions. 相似文献
147.
148.
George Adomian 《Foundations of Physics Letters》1993,6(6):603-605
In mathematical approaches to elementary particle theory, the equation [2 -
2/t2]=m2
;+g
3 has been of interest [1,2]; it describes a quartically self-coupled neutral scalar meson field. This paper applies the decomposition method [3-6] to obtain accurate non-perturbative timedevelopment of the field for this equation, or variations involving other nonlinear interactions, without the use of cutoff functions or truncations. 相似文献
149.
Three-Dimensional Modeling of the Turbulent Plasma Jet Impinging upon a Flat Plate and with Transverse Particle and Carrier-Gas Injection 总被引:4,自引:0,他引:4
Modeling results are presented concerning the turbulent thermal plasma jet impinging normally on a substrate and with transverse injection of feedstock particles and their carrier gas from a single injection tube. The k- two-equation model is employed to model the turbulence, and particle dispersion is studied considering the interaction between the moving particles and turbulent eddies and considering the effect on particle trajectories of the random variation of the turbulent fluctuating velocities in their magnitude and direction. A well-validated three-dimensional (3-D) computer code is used in the modeling. The 3-D effects due to the carrier gas injection on the jet flow field and thus on the particle trajectories and heating histories are shown to be appreciable. The radial location of the injection tube with respect to the plasma jet is shown to be a critical parameter for the study of 3-D effects, besides the carrier-gas/plasma stream mass flux ratio. Particle dispersion considerably widens the distribution of the particle trajectories and heating histories. In addition, although pertinent swirl number is often rather small, swirling may also affect the modeling results. 相似文献
150.
Molar excess mixing enthalpies h
E
, Gibbs free energies g
E
and hence entropies s
E
have been obtained using calorimetry and the vapor sorption method at 25°C for hexane isomers+2,2,4,4,6,8,8-heptamethylnonane, a highly branched C
16
. The h
E
and g
E
are negative while Ts
E
are positive, but small. The values are explained by the Prigogine-Flory theory through negative free volume contributions to h
E
and Ts
E
, counterbalanced in the case of Ts
E
by the positive combinatiorial Ts
E
for mixing molecules of different size. No contribution is seen from the interaction between methyl and methylene groups. The excess quantities are also obtained for hexane and heptane isomers mixed with n-hexadecane. Values of h
E
and Ts
E
are now strongly positive, while those of g
E
are only slightly less negative. The interpretation requires two recently advanced contributions in addition to those of the Prigogine-Flory theory: 1) a decrease of order when correlations of orientations between n-C
16
molecules in the pure liquid are replaced in the solution by weaker correlations whose strengths depend on the shapes of the lower alkane isomers. For lower alkane isomers of the same shape, but highly sterically hindered, h
E
and Ts
E
are small, manifesting, 2) a negative contribution, ascribed to a rotational ordering of n-C
16
segments on the sterically-hindered molecule. Enthalpy-entropy compensation is observed for these new contributions, arising from their rapid fall-off with increase of temperature. 相似文献