制备纳米V2O5的新方法及其电化学性能的研究

目前对锂离子电池正极材料的研究主要为达到如下目标而进行:高的比容量和能量密度,良好的循环性和寿命,资源丰富、价格便宜以及环境友好。已进行了广泛研究的LiCoO_2、LiNiO_2、LiMn_2O_4等锂离子电池正极材料,虽然具有较高的电压平台、良好的稳定性和寿命,但其容量相对较低和价格较高限制了其进一步的应用和发展。     

17O NMR Investigation of Chemical Homogeneity in Hybrid Systems

¹⁷O NMR experiments using enriched water were performed to followthe hydrolysis-condensation process of dimethyldiethoxysilanetetraethoxysilane and a 1/1 mixture of dimethyldiethoxysilane andtetraethoxysilane (H₂O/OEt = 0.5; pH = 2). The spectrarecorded over several hours time period were simulated to followquantitatively the variations of residual water, hydroxyl groups(Si–¹⁷ H) and oxo bridges (Si–¹⁷ –Si). Presence of a resonance signal due oxo bridges between di- andtetrafunctional Si units clearly demonstrates that co-condensationreactions occur to a large extent between the two alkoxides, and that thesebonds are stable during the aging period.     

Aging effect on the mechanical properties of hybrid gels

Sol-gel derived unsupported films and thin rods have been obtained from co-hydrolysis of triethoxysilane and methyldiethoxysilane. The materials are flexible, dense and transparent. Films and rods have been aged for different periods of time in air at room temperature. The elastic modulus has been measured by means of tensile or flexural tests. Measurements showed an increase of elastic modulus with aging time and showed different values for films and rods. The observed evolution of mechanical properties has been related to a corresponding structural modification as highlighted mainly by MAS-NMR studies. Analyses pointed out the crucial role of condensation processes and showed that the stiffness increase arises from the formation of relatively few bonds which link and constrain pre-existing mobile network regions.     

Theoretical treatment of first-order reversible reactions occurring in a chromatographic reactor, on the basis of consecutive reactions

Summary Analytical peak-shape equations were derived for first-order reversible reactions occurring in a chromatographic reactor by treating the reversible reactions as consecutive reactions with alternating products. The results of the analytical peak-shape equations were compared with those from a numerical solution of the partial differential equation system modeling the chromatographic reactor. For small to medium conversions the correspondence was found to be sufficiently close to enable substitution of the numerical solution in fitting procedures for the determination of rate constants. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A simple approach for improving the hybrid MMVB force field: application to the photoisomerization of s-cis butadiene

MMVB is a QM/MM hybrid method, consisting of a molecular mechanics force field coupled to a valence bond Heisenberg Hamiltonian parametrized from ab initio CASSCF calculations on several prototype molecules. The Heisenberg Hamiltonian matrix elements Q(ij) and K(ij), whose expressions are partitioned here into a primary contribution and second-order correction terms, are calculated analytically in MMVB. When the original MMVB force field fails to produce potential energy surfaces accurate enough for dynamics calculations, we show that significant improvements can be made by refitting the second-order correction terms for the particular molecule(s) being studied. This "local" reparametrization is based on values of K(ij) extracted (using effective Hamiltonian techniques) from CASSCF calculations on the same molecule(s). The method is demonstrated for the photoisomerization of s-cis butadiene, and we explain how the correction terms that enabled a successful MMVB dynamics study [Garavelli, M.; Bernardi, F.; Olivucci, M.; Bearpark, M. J.; Klein, S.; Robb, M. A. J Phys Chem A 2001, 105, 11496] were refitted.     

Rigid nanoscopic containers for highly dispersed, stable metal and bimetal nanoparticles with both size and site control

We demonstrate a novel strategy for the preparation of mesoporous silica-supported, highly dispersed, stable metal and bimetal nanoparticles with both size and site control. The supporting mesoporous silica, functionalized by polyaminoamine (PAMAM) dendrimers, is prepared by repeated Michael addition with methyl acrylates (MA) and amidation reaction with ethylenediamine (EDA), by using aminopropyl-functionalized mesoporous silica as the starting material. The encapsulation of metal nanoparticles within the dendrimer-propagated mesoporous silica is achieved by the chemical reduction of metal-salt-impregnated dendrimer-mesoporous silica by using aqueous hydrazine. The site control of the metal or bimetal nanoparticles is accomplished by the localization of inter- or intradendrimeric nanoparticles within the mesoporous silica tunnels. The size of the encapsulated nanoparticles is controlled by their confinement to the nanocavity of the dendrimer and the mesopore. For Cu and Pd, particles locate at the lining of mesoporous tunnels, and have diameters of less than 2.0 nm. For Pd/Pt, particles locate at the middle of mesoporous tunnels and have diameters in the range of 2.0-4.2 nm. The Pd and Pd/Pt nanoparticles are very stable in air, whereas the Cu nanoparticles are stable only in an inert atmosphere.     

Thermodegradation kinetics of a hybrid inorganic-organic epoxy system

Lifetime of the epoxy system formed by diglycidyl ether of bisphenol A, DGEBA/4,4′-diaminediphenylmethane, DDM, modified with the silsesquioxane, glycidylisobutyl-POSS, was calculated from thermogravimetric analysis. The activation energy of the decomposition of this system was evaluated by the integral method developed by Flynn-Wall-Ozawa (E = 88.9 ± 2.1 kJ mol⁻¹) and by Coats and Redfern method (E = 85.2 ± 1.5 kJ mol⁻¹). The kinetic parameters have been used to estimate the lifetime of the system POSS/DGEBA/DDM. The obtained results by two different ways are similar.     

甲烷直接氧化制甲醇Ⅱ．催化膜反应器（CMR）

采用溶胶－凝胶（Ｓｏｌ－Ｇｅｌ）法制备了微孔结构均匀的“ＳｉＯ＿２／陶瓷”膜和“Ｍｏ－Ｃｏ－·Ｏ／ＳｉＯ＿２／陶瓷”催化功能膜，并用ＸＲＤ、ＳＥＭ和孔径测定等技术进行了表征。在常压、５００～７００℃的条件下，在催化膜反应器（ＣＭＲ）中考察了甲烷氧化制甲醇的反应。在相似的反应条件下（转化率为１．０％），用ＣＭＲ（甲醇选择性１１．２％）可获得较固定床反应器（甲醇选择性４．５％）高得多的甲醇选择性。     

Methane production from synthesis gas using a mixed culture ofR. rubrum M. barkeri,and M. formicicum

The components of synthesis gas, CO, H₂, and CO₂, may be converted into CH₄ biologically through either acetate or H₂/CO₂ as intermediates. Of these two routes, conversion through H₂/CO₂ is preferred. This paper presents results of mixed-culture studies employing the photosynthetic bacteriumR. rubrum for converting CO to CO₂ and H₂ by the water gas shift reaction and two methanogens,M. formicicum andM. barkeri, for converting CO₂ and H₂ into CH₄. Results are presented for triculture operation in two types of reactors, the packed bubble column and the trickle-bed reactor.     

有机-无机杂化配位聚合物{[C12H28N2][(Pb3I8) (DMF)2]•2DMF}n的晶体及电子结构

合成了一种新颖有机-无机杂化配位聚合物{[C₁₂H₂₈N₂] [(Pb₃I₈)(DMF)₂]•2DMF}_n, 并进行了红外、紫外、热重表征, 采用X射线衍射方法确定了晶体结构. 结构解析表明, 整个分子由阳离子(双质子化的N,N'-二丁基哌嗪)及聚阴离子链([(Pb₃I₈)(DMF)₂]_n^2-)组成, 它们之间由静电作用结合在一起形成一维链状配位聚合物. 依据晶体结构数据, 采用Gaussian03程序对产物进行量子化学计算.