钛酸酯催化碳酸二甲酯与苯酚酯交换反应的研究

用Ti(OBu)4、Ti[OCH(CH3)2]4和T(OPh)43种钛酸酯作催化剂,对碳酸二甲酯（DMC）与苯酯的酯交换反应进行了研究。以Ti(OBu)4为催化剂,对反应的热力学、原料配比、催化剂用量、反应温度和反应时间等工艺条件进行了考察 。实验表明,当DMC：苯酚：Ti(OBu)4(摩尔比）＝1.5:1:0.05、反应温度175℃、反应时间为25h时,酯交换反应基本上达到平衡,苯酚的转化率为47.4％,MPC的选择性为90.9%,DPC的选择性为9.14%.     

Crystal structures of Na1/2Ln1/2TiO3 (Ln: La, Eu, Tb)

Neutron powder diffraction studies of Na_1/2La_1/2TiO₃ and Na_1/2Tb_1/2TiO₃, and a synchrotron X-ray powder diffraction study of Na_1/2Eu_1/2TiO₃ have been carried out. Rietveld refinement of the structures confirmed that Na_1/2Eu_1/2TiO₃ and Na_1/2Tb_1/2TiO₃ crystallizes in GdFeO₃ type of structure (space group Pbnm). The ambiguity in the literature regarding the crystal structure of Na_1/2La_1/2TiO₃ has been resolved and the correct space group is found to be . A detailed list of refined structural parameters of these compounds is presented for the first time.     

Radwaste Immobilization by Structural Modification—the Crystallochemical Properties of SYNROC,a Titanate Ceramic

New studies utilizing electron microscopic techniques have revealed the immobilization of radionuclides in crystalline ceramic waste forms to be not merely a question of substituting waste elements into the appropriate crystallographic sites of a host matrix. Rather than entering the ceramic as a “continuous” solid solution it has been found that the incorporation of highly radioactive waste elements is commonly accompanied by structural modification. This may take the form of cation ordering, crystallographic shear, or twinning on a unit cell scale. Such mechanisms considerably enhance the capacity of a ceramic to immobilize (simulated) radwaste and impart to it the flexibility to respond to inevitable variations in wastestream composition.     

The story of Sr2RuO4

This article reports on the experiments performed in the Sr–Ru–O system, the motivation behind them and their impact on basic research and device applications. It refers to the time from 1987 to 2003, with emphasis on the occurrences before the discovery of superconductivity in Sr₂RuO₄ in 1994. Apart from the title compound Sr₂RuO₄ itself and related ruthenates, it touches on many different topics like titanates, ferrates, high-T_c superconducting cuprates, crystal growth by floating zone melting and thin films as well as fundamental and applied research.     

Raman and ESR study of sol–gel materials from ZnO–TiO2–B2O3 system

The paper studies the materials from ZnO–TiO₂–B₂O₃ ternary system, obtained by sol–gel method [1] and [2], starting from organic and inorganic precursors. The obtained samples are investigated by FTIR and Raman spectroscopy, which provide structural information, at molecular level. FTIR absorption maxima are identified and discussed according to literature data. Raman spectra are acquired by a Raman Jasco NRS-3100 spectrometer, at 532 nm wavelength and put in evidence characteristic vibration modes for all three oxide components. ESR spectra were plotted with the aid of a JES-FA 100-JEOL Japan spectrometer and titanium surrounding is investigated.     

Catalytic efficiency of some novel nanostructured heterogeneous solid catalysts in pyrolysis of HDPE

In the present study, the catalytic conversion of high density polyethylene (HDPE) to useful products has been investigated in the presence of BaTiO₃ based catalysts in a micro steel reactor at 350 °C and 30 min reaction time. The catalysts, including BaTiO₃, Pb/BaTiO₃, Co/BaTiO₃ and Pb–Co/BaTiO₃ were prepared in the laboratory by reactive calcination method and characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-rays (EDX), Surface Area Analyzer (SAA) and X-rays Diffractometry (XRD). The product yields (over all yields and yields of liquid, gas and coke/residue) as a function of individual catalyst concentration was studied. The result indicated a promising effect of the catalysts used on conversion to liquid products and their composition in term of carbon range (C₆ – >C₃₀) & hydrocarbon group types (paraffin's, olefins, naphthenics, and aromatics). Among the catalysts used, Pb–Co/BaTiO₃ gave the maximum yield of liquid products (86%) when used in 1 wt % loading. The same catalyst gave the average yield (20–25%) of different range hydrocarbons i.e. C₆–C₁₂, C₁₃–C₁₆, C₁₇–C₂₀ and C₂₀–C₃₀. Inversely, the un-doped BaTiO_3, favored the formation of C₆–C₁₂ and C₁₃–C₁₆ range hydrocarbons, whereas Pb doped BaTiO₃ and Co doped BaTiO₃ enhanced the yield of C₁₃–C₁₆, and C₂₀–C₃₀ range hydrocarbons. Regarding the hydrocarbon group types, all catalysts significantly increased the formation of paraffins and reduced olefins and naphthenes.     

Structural and dielectric properties in the (Ba1−xCax)(Ti0.95Zr0.05)O3 ceramics

Lead-free (Ba_1−xCa_x)(Ti_0.95Zr_0.05)O₃ (x = 0.05-0.40) (BCZT) ceramics were prepared by solid-state reaction technique. XRD results show that the samples in the composition range of 0.05 ≤ x ≤ 0.25 exhibit pure perovskite structures and undergo a polymorphic phase transitions from orthorhombic to tetragonal phase around room temperature. The biphasic structures are detected at x ≥ 0.30 and the dielectric peaks become broad and dielectric constants decrease with increasing Ca content. Ca replacement at Ba site leads to diffuseness, whereas Ca occupancy at Ti site leads to decrease of the T_c.     

The influence of temperature on the structural behaviour of sodium tri- and hexa-titanates and their protonated forms

The thermal stability of Na₂Ti₃O₇ and Na₂Ti₆O₁₃, together with that of their protonated forms was investigated. The influence of temperature on the structural behaviour of tri- and hexa-titanates was studied using DTG, XRD, FTIR and FT-Raman. These results were correlated with the nature of the exchangeable cations using elemental analysis and N₂-sorption. The tunnel structure of Na₂Ti₆O₁₃ revealed a higher thermal stability compared to the layered structure of Na₂Ti₃O₇ that shows traces of dimerisation above 800 °C. The sodium forms were observed to be more thermally stable compared to their protonated forms. However, analysis show that ‘H₂Ti₆O₁₃’ is much more thermally stable than the layered H₂Ti₃O₇ which go through structural changes above 250 °C and suffer a complete structural collapse into anatase/rutile above 800 °C. It was obvious that thermal stability was significantly influenced by the nature of the exchangeable cations and the degree of ion-exchange.     

Hierarchical Titanate Nanostructures through Hydrothermal Treatment of Commercial Titania Powders

Hierarchical titanate nanostructures were hydrothermally synthesized in concentrated base solutions using commercial titania powders as starting materials. By varying the base concentration, nanowire arrays, flowers of nanosheets and nanotubes, and urchin‐like nanostructures of nanowires and nanotubes were sequentially fabricated. If the NaOH concentration was higher than 6 M , hydrated Na₂Ti₆O₁₃ nanowire arrays, with nanowire diameters of 20–90 nm and an aspect ratio of 1100–5000, were produced at suitable reaction temperatures over a large area. In 10 M KOH solutions, aligned nanowires with a diameter of 30 nm and a lenght of 80 μm formed. In 4 M NaOH solutions, micrometer‐sized flowers of nanotubes and nanosheets formed. Reactions in 2 M NaOH solutions produced urchin‐like materials with a size of ca. 10 μm that were composed of nanotubes and nanowires. The adsorption behavior of the urchin‐like materials resembled macroporous materials with micropores. Since both base concentration and reaction temperature affected the reaction rate, the formation of various titanate nanostructures was proposed as a growth speed controlled process.     

Na6[Ti5O12(OH)2]: A New Titanate Containing $\rm{{_{\infty }^{1}}}$[Ti5O12(OH)2]6− Ribbons

Na₆[Ti₅O₁₂(OH)₂] is the first structurally characterized sodium oxohydroxotitanate. The compound can be prepared via hydrothermal treatment of TiO₂ (Anatas) in NaOH (10n ) for 96 h at 250° in an autoclave. The crystal structure of Na₆[Ti₅O₁₂(OH)₂] consists of infinite ribbons [Ti₅O₁₂(OH)₂]^6?. The orthorhombic arrangement has Pbcn (No. 60) symmetry with the lattice constants a=18.668(4) Å, b=6.5333(13) Å, and c=9.829(2) Å.