低于300℃时两种氧化铈材料对稀燃阶段NOx存储性能的影响

研究了低于300 ℃时两种氧化铈对稀燃阶段NO_x存储性能的影响,催化剂由2%（w）Pt/Al₂O₃（PA）与CeO₂-X（X=S,I）机械混合制备. X射线衍射（XRD）,BET表面积和扫描电子显微镜（SEM）用于表征材料的物理结构. X射线光电子能谱（XPS）和H₂程序升温还原（H₂-TPR）用于表面Ce³⁺和活性氧定量. 原位漫反射傅里叶变换红外光谱（in-situ DRIFTS）用于分析表面NO_x吸附物种. 相比于CeO₂-I,CeO₂-S 具有优良的物理化学性能,包括高比表面积、丰富的空隙结构、较高的抗老化能力及表面Ce³⁺浓度. 因而,Pt/Al₂O₃+CeO₂-S 表现出优异的NO_x存储能力. 此外,PA+CeO₂-X（X=S,I）上存在Pt 与CeO₂之间的相互作用,可提高表面氧物种的活性进而促进NO氧化及NO_x存储. PA+CeO₂-S上的这种相互作用要强于PA+CeO₂-I. 研究表明,表面Ce³⁺浓度和活性氧含量对NO_x存储起到重要作用. 然而经过水热处理后,Pt 与老化的氧化铈（ACS,ACI）之间的相互作用降低,并且两种氧化铈NO_x存储性能显著下降. 另外,与PA+ACS（ACI）相比,PA+PACS（PACI）样品NO_x存储能力得到改善,这归因于表面氧物种活性增加能促进硝酸盐的形成.     

Synthesis and Investigation of Soluble Polymer-supported Dendrimers

Poly（ethylene glycol） （PEG）-supported dendrimers have been synthesized using 2.4,6-trichloro-1,3,5-triazine （TCT） as dendrons and tris（hydroxymethyl）aminomethane as tinkers with high loading capacity, excellent solubility and thermal stability by divergent method. The new synthesized PEG-supported G2.0 dendrimer has 10 times as large functional group loading capacity as commercial PEG3400 with overall yield 44.0%.     

Thermodynamic properties of hydrated sodium l-threonate Na(C4H7O5)·H2O(s)

Low-temperature heat capacities of the compound Na(C₄H₇O₅)·H₂O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are Δ_transH_m = (5.75 ± 0.01) kJ mol⁻¹ and Δ_transS_m = (18.47 ± 0.02) J K⁻¹ mol⁻¹. The enthalpy and entropy of the dehydration are Δ_dH_m = (15.35 ± 0.03) kJ mol⁻¹ and Δ_dS_m = (41.35 ± 0.08) J K⁻¹ mol⁻¹. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations.     

Thermodynamic quantities for the interaction of SO 4 2− with H+ and Na+ in aqueous solution from 150 to 320°C

The aqueous reactions,

Enthalpies of Phase Transitions and Heat Capacity of TbCl3 and Compounds Formed in TbCl3–MCl Systems (M=K, Rb, Cs)

The molar enthalpies of the solid–solid and solid–liquid phase transitions were determined by differential scanning calorimetry for pure TbCl₃ and KTb₂Cl₇, RbTb₂Cl₇, CsTb₂Cl₇, K₃TbCl₆, Rb₃TbCl₆ and Cs₃TbCl₆ compounds. Both types of compounds, i.e. M₃TbCl₆ and MTb₂Cl₇ (M=K, Rb, Cs) melt congruently and show additionally a solid–solid phase transition with a corresponding enthalpy Δ_trs H ⁰ of 6.1, 7.6 and 7.0 kJ mol^–1 for potassium, rubidium and caesium M₃TbCl₆ compounds andΔ_trs H ⁰ of 17.1 (rubidium) and of 12.1 and 10.9 kJ mol^–1 (caesium) for MTb₂Cl₇ compounds, respectively. The enthalpies of fusion were measured for all the above compounds with the exception of Rb₃TbCl₆ and Cs₃TbCl₆. The heat capacities of the solid and liquid compounds have been determined by differential scanning calorimetry (DSC) in the temperature range 300–1100 K. The experimental heat capacity strongly increases in the vicinity of a phase transition, but varies smoothly in the temperature ranges excluding these transformations. C _p data were fitted by an equation, which provided a satisfactory representation up to the temperatures of C _p discontinuity. The measured heat capacities were checked for consistency by calculating the enthalpy of formation of the liquid phase, which had been previously measured. The results obtained agreed satisfactorily with these experimental data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat Capacities of Aqueous Solutions of Acetone; 2,5-Hexanedione; Diethyl Ether; 1,2-Dimethoxyethane; Benzyl Alcohol; and Cyclohexanol at Temperatures to 523 K

The heat capacities of aqueous solutions of acetone, 2,5-hexanedione, diethyl ether, 1,2-dimethoxyethane, benzyl alcohol and cyclohexanol at concentrations of 0.1 to 1.0 mol⋅kg⁻¹ were determined at temperatures of 298.15, 423.15, 473.15 and 523.15 K and pressures up to 28 MPa. The measurements were performed at ambient conditions using the commercial Picker differential flow calorimeter and at high temperatures and pressures with a customized Picker type calorimeter constructed at the Blaise Pascal University, Clermont-Ferrand. Standard molar heat capacities were obtained by weighted extrapolation to the infinite dilution limit. The contributions of –CO–, –O– and –OH groups to the standard molar volume and standard molar heat capacity were determined from the newly determined and literature data. The variation of the three oxygen-containing group contributions with temperature and molecular structure is examined qualitatively.     

Modulated differential scanning calorimetry in the glass transition region

Temperature-modulated calorimetry (TMC) allows the experimental evaluation of the kinetic parameters of the glass transition from quasi-isothermal experiments. In this paper, model calculations based on experimental data are presented for the total and reversing apparent heat capacities on heating and cooling through the glass transition region as a function of heating rate and modulation frequency for the modulated differential scanning calorimeter (MDSC). Amorphous poly(ethylene terephthalate) (PET) is used as the example polymer and a simple first-order kinetics is fitted to the data. The total heat flow carries the hysteresis information (enthalpy relaxation, thermal history) and indications of changes in modulation frequency due to the glass transition. The reversing heat flow permits the assessment of the first and higher harmonics of the apparent heat capacities. The computations are carried out by numerical integrations with up to 5000 steps. Comparisons of the calculations with experiments are possible. As one moves further from equilibrium, i.e. the liquid state, cooperative kinetics must be used to match model and experiment.On leave from Toray Industries, Inc., Otsu, Shiga 520, Japan.This work was supported by the Division of Materials Research, National Science Foundation, Polymers Program, Grant # DMR 90-00520 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy at Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy, under contract number DE-AC05-96OR22464. Support for instrumentation came from TA Instruments, Inc. Research support was also given by ICI Paints, and Toray Industries, Inc.     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

Sample capacity in open tubular and micro-packed columns for GC

Equations have been derived from which the maximum sample size which may be loaded on a column without significantly affecting the performance may be calculated. It is shown that micro-packed columns can handle a sample which is as much as forty times larger than that which can be loaded onto wall-coated open tubular columns with comparable conditions.