Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters

The structures and relative stabilities of high‐spin ⁿ⁺¹Au_n?1Ag and ⁿAu_n?1Ag⁺ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Au_n?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Au_n clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Au_n?1Ag neutral and cationic species, ⁵Au₃Ag, ³AuAg and ⁵Au₄Ag⁺ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Stress overshoot of polymer solutions at high rates of shear; Polystyrene with bimodal molecular weight distribution

Overshoot of shear stress, σ, and the first normal stress difference, N₁, in shear flow was investigated for dilute solutions of polystyrene with very high molecular weight in concentrated solution of low M PS. In the case that the matrix was a nonentangled system, behavior of overshoot was similar to that of dilute solution of high M PS in pure solvent. The magnitudes of shear, γ_σm and γ_Nm, corresponding to the peaks of σ and N₁ lay on the universal functions of γ˙τ_R, respectively, proposed for dilute solutions in pure solvent. Here τ_R is the Rouse relaxation time for high M PS in the blend evaluated from dynamic modulus at high frequencies. In the case that the matrix was an entangled system, an additional σ peak was observed at high rates of shear at times corresponding to γ_σm = 2–3. This peak can be assigned to the motion of low M chains in entanglement network. When the matrix was entangled, stress overshoot was observed even at relatively low rates of shear, say γ˙τ_R < 10⁻². This is probably due to the motion of high M chains in entanglement of all the chains. In this case the γ_σm and γ_Nm values were higher than those expected for entangled chains of monodisperse polymer in pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2043–2050, 2000     

内嵌镧金属富勒烯的高产率合成及异构体比例调控

采用电弧放电法制备内嵌镧金属富勒烯的原灰,通过改变氦气压力及电流强度来提高内嵌镧金属富勒烯产率。原灰由1,2,4-三氯苯提取并回溶入甲苯后,利用分析型高相液相色谱（HPLC）对提取液中各富勒烯组分进行分析。通过分别衡量3种常见含镧金属富勒烯La@C_2v-C₈₂、La@C_s-C₈₂和La₂@C₈₀与C₈₄的相对峰面积比,探讨了氦气压力和电流强度等对3种金属富勒烯产率的影响。实验结果表明,氦气压力与电流强度共同决定了金属富勒烯的产率,在（1）低电流高氦气压、（2）中等电流中等氦气压、（3）高电流低氦气压的条件下都可以高产率地获得含镧金属富勒烯。此外,调整电流强度和氦气压力可以改变La@C_2v-C₈₂和La@C_s-C₈₂的相对比例。例如,在电流为100、120 A或氦气压为20、35 kPa时,此前认为的"minor"异构体La@C_s-C₈₂的含量甚至高于"major"异构体La@C_2v-C₈₂。我们还发现,降低电流强度或减小氦气压力可促进La₂@C₈₀的生成,这表明La₂@C₈₀与La@C₈₂的形成过程可能是不同的。     

内嵌镧金属富勒烯的高产率合成及异构体比例调控

采用电弧放电法制备内嵌镧金属富勒烯的原灰,通过改变氦气压力及电流强度来提高内嵌镧金属富勒烯产率。原灰由1,2,4-三氯苯提取并回溶入甲苯后,利用分析型高相液相色谱(HPLC)对提取液中各富勒烯组分进行分析。通过分别衡量3种常见含镧金属富勒烯La@C2v-C82、La@Cs-C82和La_2@C_(80)与C84的相对峰面积比,探讨了氦气压力和电流强度等对3种金属富勒烯产率的影响。实验结果表明,氦气压力与电流强度共同决定了金属富勒烯的产率,在(1)低电流高氦气压、(2)中等电流中等氦气压、(3)高电流低氦气压的条件下都可以高产率地获得含镧金属富勒烯。此外,调整电流强度和氦气压力可以改变La@C2v-C82和La@Cs-C82的相对比例。例如,在电流为100、120 A或氦气压为20、35 k Pa时,此前认为的"minor"异构体La@Cs-C82的含量甚至高于"major"异构体La@C2v-C82。还发现降低电流强度或减小氦气压力可促进La_2@C_(80)的生成,这表明La_2@C_(80)与La@C82的形成过程可能是不同的。     

Random copolymer of butadiene and propylene prepared with TiCl4–Et3Al–phosgene catalyst

The copolymerization of butadiene and propylene was investigated. It was found that the catalyst system of TiCl₄–Et₃Al–COCl₂ yields a random copolymer of high molecular weight with a small amount of gel polymer above room temperature. Tetrachloroethylene was a good solvent for the production of high polymer containing a high proportion of propylene units in high yield. The fractionation and the analysis of degradation experiments of copolymer indicate that the copolymer is of random distribution of propylene units in the copolymer. However, the monomer reactivity ratios, r_BD = 6.36 and r_Pr = 0.42, suggest some degree of blocked character. The properties of the copolymer were superior to those of cis-1,4–polybutadiene, especially in resistance to thermal aging.     

Binary Compounds of Rhodium and Zinc: RhZn,Rh2Zn11, and RhZn13

The title compounds were prepared by reaction of the elements at elevated temperatures in sealed silica tubes. Single crystals of RhZn and RhZn₁₃ were obtained by slow cooling of samples with a high zinc content after dissolving the zinc‐rich matrix in hydrochloric acid. Their crystal structures were determined from single‐crystal X‐ray diffractometer data. RhZn has a CsCl type structure: Pm3m, a = 300.9(1) pm. RhZn₁₃ has a CoZn₁₃ type structure: C2/m, a = 1090.8(2) pm, b = 753.7(2) pm, c = 512.7(1) pm, β = 101.02(2)°. The structure of Rh₂Zn₁₁ is isotypic with Cu₅Zn₈, the γ‐brass structure. It was refined from X‐ray diffractometer powder data: I43m, a = 909.1(1) pm. In these structures all atoms have high coordination numbers. The structure of RhZn₁₃ contains relatively large unoccupied voids. It is suggested that they accommodate nonbonding electrons. Electrical conductivity measurements of Rh₂Zn₁₁ and RhZn₁₃ indicate metallic behavior, however, with an unexpectedly high resistivity for Rh₂Zn₁₁. The expected Pauli paramagnetism of these compounds is overcompensated by the core diamagnetism, suggesting a low density of states at the Fermi level especially for Rh₂Zn₁₁. This correlates with the high electrical resistivity of this compound.     

POLYMERIZATION OF METHYL METHACRYLATE WITH ORGANOLANTHANIDES AS SINGLE-COMPONENT CATALYSTS*

 It was first found that Ind₂Y(μ-Et)₂AlEt₂ and Ind₂LnN(i-Pr)₂ (Ln = Y, Yb) exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -30 to 50℃. PMMA with high molecular weight (7.8 × l0^-5) and high isotacticity (94%) can be obtained by using Ind₂Y(μ-Et)₂AlEt₂, and narrow molecular weight distribution (M_w/M_n < 1.5) can be obtained by using Ind₂LnN(iPr)₂(Ln = Y, Yb).     

Partial Oxidation of Methane to Methanol with Oxygen or Air in a Nonequilibrium Discharge Plasma

The partial oxidation of methane to methanol with oxygen or air was investigated experimentally and theoretically in a dielectric-barrier discharge (DBD). The predominant parameters of specific electric energy, oxygen content, flow rate, temperature, and gas pressure were determined in CH ₄ /O ₂ and CH ₄ /air mixtures. Optimum selectivities toward methanol formation were found at an oxygen concentration of about 15% in both feed gas mixtures. Low specific energy favors the selectivity toward methanol and suppresses the formation of carbon oxides. The experiments indicate that high methanol selectivities can be obtained at high methane conversion. The highest methanol yield of 3% and the highest methanol selectivity of about 30% were achieved in CH ₄ /O ₂ mixtures. In CH ₄ /air mixtures, as high as 2% methanol yield was also obtained. In addition, other useful products, like ethylene, ethane, propane, and ethanol, were detected. Experiment and numerical simulations show that the formation of H ₂ O and CO has a strong negative influence on methanol formation.     

Controllable Fabrication of Tungsten Oxide Nanoparticles Confined in Graphene‐Analogous Boron Nitride as an Efficient Desulfurization Catalyst

Tungsten oxide nanoparticles (WO_xNPs) are gaining increasing attention, but low stabiliity and poor dispersion of WO_xNPs hinder their catalytic applications. Herein, WO_xNPs were confined in graphene‐analogous boron nitride (g‐BN) by a one‐step, in situ method at high temperature, which can enhance the interactions between WO_xNPs and the support and control the sizes of WO_xNPs in a range of about 4–5 nm. The as‐prepared catalysts were applied in catalytic oxidation of aromatic sulfur compounds in which they showed high catalytic activity. A balance between the W loading and the size distribution of the WO_xNPs could govern the catalytic activity. Furthermore, a synergistic effect between g‐BN and WO_xNPs also contributed to high catalytic activity. The reaction mechanism is discussed in detail and the catalytic scope was enlarged.     

Electrophoretic flow of interacting polymer chains: Effects of temperature,polymer concentration,and porosity

Using a Monte Carlo simulation in three dimensions, we studied the variation of the root-meansquare (rms) displacement (R_rms) of polymer chains with time and the rates of their mass transfer (j) as a function of biased field (B), polymer concentration (p), chain length (L_c), porosity (p_s), and temperature (T). In homogeneous/annealed system, the rms displacement of the chains shows a drift-like behavior, R_rms ∼ t, in the asymptotic time regime preceded by a subdiffusive power-law (R_rms ∼ t^k, with k < 1/2) at high p. The subdiffusive regime expands on increasing L_c and p but reduces on increasing T or B. In quenched porous media, the drift-like behavior of R_rms persists at low barrier concentration (p_b) and high T. However, at high p_b and/or low T, chains relax into a subdrift and/or subdiffusive behavior especially with high p or long L_c. Flow of chains is measured via an effective permeability (σ) using a linear response assumption. In annealed system, σ increases monotonically with B at high T and low p but varies nonmonotonically at low T, high p and high L_c. We find that σ decays with L_c, σ ∼ L, where α depends on B, p and T with a typical value a α ∼ 0.43−0.64 for p = 0.1-0.3 at B = 0.5. Further, σ decays with p, σ ∼ − Cp with a decay rate C sensitive to T and B. In quenched porous media, even at low pb and high T, σ varies nonmonotonically with bias, i.e., the increase of σ is followed by decay on increasing the bias beyond a characteristic value (B_c). This characteristic bias seems to decrease logarithmically with barrier concentration, B_c ∼ −klnp_b. The prefactor k depends on the chain length, k ≈ 0.35 for shorter chains (L_c = 20, 40) and ≈ 0.15 for longer chains (L_c = 60). Scaling dependence of σ on L_c similar to that in annealed system is also observed in porous media with different values of exponent α. The current density shows a nonlinear power-law response, j ∼ B^σ, with a nonuniversal exponent δ ≈ 1.10−1.39 at high temperatures and low barrier concentrations.     

High‐Quality Gasoline Directly from Syngas by Dual Metal Oxide–Zeolite (OX‐ZEO) Catalysis

Despite significant efforts towards the direct conversion of syngas into liquid fuels, the selectivity remains a challenge, particularly with regard to high‐quality gasoline with a high octane number and a low content of aromatic compounds. Herein, we show that zeolites with 1D ten‐membered‐ring (10‐MR) channel structures such as SAPO‐11 and ZSM‐22 in combination with zinc‐ and manganese‐based metal oxides (Zn_aMn_bO_x) enable the selective synthesis of gasoline‐range hydrocarbons C₅–C₁₁ directly from syngas. The gasoline selectivity reached 76.7 % among hydrocarbons, with only 2.3 % CH₄ at 20.3 % CO conversion. The ratio of isoparaffins to n‐paraffins was as high as 15, and the research octane number was estimated to be 92. Furthermore, the content of aromatic compounds in the gasoline was as low as 16 %. The composition and structure of Zn_aMn_bO_x play an important role in determining the overall activity. This process constitutes a potential technology for the one‐step synthesis of environmentally friendly gasoline with a high octane number from a variety of carbon resources via syngas.     

初始钙-磷物质的量比值对超长羟基磷灰石纳米纤维微观结构的影响

羟基磷灰石(HA)晶体的形核和生长与表面活性剂、初始钙-磷物质的量比值(nCa,0/nP,0)密切相关.因此,本研究以油酸为表面活性剂制备高柔韧超长HA纳米纤维,利用X射线衍射(XRD)、FTIR、场发射扫描电镜(FESEM)和能量色散X射线谱(EDS)探究了不同nCa,0/nP,0对HA纳米纤维微观结构的影响,并基于...     

Highly Enantioselective Catalytic System for Asymmetric Copolymerization of Carbon Dioxide and Cyclohexene Oxide

A new ligand can be easily prepared, and its intramolecular dinuclear zinc complexes act as a high performance catalyst for the asymmetric alternating copolymerization of cyclohexene oxide and CO₂ under very mild conditions (1 atm CO₂, room temperature), affording completely alternating polycarbonates with up to 93.8 % enantiomeric excess (ee) and 98 % yield. A high M_n value of 28 600 and a relatively narrow polydispersity (M_w/M_n ratio) of 1.43 were also achieved.     

ZrMn Oxides for Aqueous‐Phase Ketonization of Acetic Acid: Effect of Crystal and Porosity

Aqueous‐phase ketonization of bio‐based acetic acid is important to improve the conversion efficiency of biomass resources. In this study, ZrMn mixed oxides (ZrMnO_x) with high aqueous‐phase ketonization activity are synthetized through a carbonization/oxidation method (COM) and solvothermal method (STM). The results show that ZrMnO_x prepared by COM possesses tetragonal ZrO₂, and hausmannite Mn₃O₄ is observed only at a high oxidation temperature of 750 °C. Low‐temperature and long oxidation results in decreased crystallinity and crystallite size, which is related to highly dispersed Mnⁿ⁺ species. The catalysts with improved acid sites possess high ketonization activity. Surface areas and pore size of ZrMnO_x synthetized by STM are controlled by the solvents for thermal treatment. Compared with water as solvent, ethanol increases the surface area and pore size, resulting in high ketonization activity.     

Linear Free‐Energy Relationships between a Single Gas‐Phase Ab Initio Equilibrium Bond Length and Experimental pKa Values in Aqueous Solution

Remarkably simple yet effective linear free energy relationships were discovered between a single ab initio computed bond length in the gas phase and experimental pK_a values in aqueous solution. The formation of these relationships is driven by chemical features such as functional groups, meta/para substitution and tautomerism. The high structural content of the ab initio bond length makes a given data set essentially divide itself into high correlation subsets (HCSs). Surprisingly, all molecules in a given high correlation subset share the same conformation in the gas phase. Here we show that accurate pK_a values can be predicted from such HCSs. This is achieved within an accuracy of 0.2 pK_a units for 5 drug molecules.     

SrZn11: a new binary compound with the BaCd11 structure

Single crystals of strontium undecazinc, SrZn₁₁, were obtained when decomposing SrZn₂ under conditions of high pressure and high temperature. The new binary Sr–Zn compound crystallizes in the space group I4₁/amd (BaCd₁₁ structure type) with one Sr position (m2) and three Zn sites (m2, .2/m., 1). The structure is described in terms of all‐face‐capped Zn₈ tetrahedra as the central building unit, defined by the Zn atoms on .2/m. and 1. The building units are condensed into chains by the central tetrahedra sharing edges, and the chains are interconnected by shared capping atoms. The resulting three‐dimensional framework of Zn atoms yields channels that are occupied by Sr and Zn atoms on the high‐symmetry m2 positions.     

Coordinative Approach to Mediated Electron Transfer: Ruthenium Complexed to Native Glucose Oxidase

Catalytically and electrocatalytically very active and stable are the complexes Ru(LL)-GO, which are extremely readily accessible from glucose oxidase (GO) and the Ru^II complexes cis-[Ru(LL)₂Cl₂] (LL=bpy, phen). These provide an unprecedentedly high amplification coefficient I/I_o (see cyclic voltammograms) even at high scan rates and, correspondingly, very high rates of intramolecular electron transfer.     

Metal-catalysed organic transformations in water: From bromination to polymerisation

Reaction ofα,Β-unsaturated aromatic carboxylic acids with KBr and H₂O₂ in the presence of Na₂MoO₄·2H₂O in aqueous medium affordsΒ-bromo alkenes in high yields. Metallocene dichlorides, Cp₂MCl₂ (M = Ti, Zr, or V) catalyse polymerisation of olefins in aqueous medium to afford high molecular weight polymers with low molecular weight distribution.     

Studies on the polymerization of ethyl acrylate. III. Effect of temperature on the solvent-transfer reaction

The effect of temperature on transfer constants for different solvents in the polymerization of ethyl acrylate was observed. Activation energy differences (E_trS ? E_p) and frequency factors were computed. It is observed that high frequency factors are associated with high activation energies. Values of E_trS were calculated by an approximate method and were compared with the available data on methyl methacrylate, isobutyl methacrylate, and styrene.     

Hierarchically Porous Carbons Derived from Metal–Organic Framework/Chitosan Composites for High‐Performance Supercapacitors

Hierarchically porous carbon materials with high surface areas are promising candidates for energy storage and conversion. Herein, the facile synthesis of hierarchically porous carbons through the calcination of metal–organic framework (MOF)/chitosan composites is reported. The effects of the chitosan (CS) additive on the pore structure of the resultant carbons are discussed. The corresponding MOF/chitosan precursors could be readily converted into hierarchically porous carbons (NPC‐V, V=1, 2, 4, and 6) with much higher ratios of meso‐/macropore volume to micropore volume (V_meso‐macro/V_micro). The derived carbon NPC‐2 with the high ratio of V_meso‐macro/V_micro=1.47 demonstrates a high specific surface area of 2375 m² g^?1, and a high pore volume of 2.49 cm³ g^?1, as well as a high graphitization degree, in comparison to its counterpart (NPC) without chitosan addition. These excellent features are favorable for rapid ion diffusion/transport, endowing NPC‐2 with enhanced electrochemical behavior as supercapacitor electrodes in a symmetric electrode system, corresponding to a high specific capacitance of 199.9 F g^?1 in the aqueous electrolyte and good rate capability. Good cycling stability is also observed after 10 000 cycles.