Thermal Activation of Molecular Tungsten Halide Clusters with the Retention of an Octahedral Metal Framework and the Catalytic Dehydration of Alcohols to Olefins as a Solid Acid Catalyst

When the molecular tungsten halide cluster (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O, with an octahedral metal framework, is heated to 50 and 150 °C in flowing helium gas, it changes into (H₃O)₂[(W₆Cl₈)Cl₆] and [(W₆Cl₈)Cl₄(H₂O)₂], respectively. Activation at 250 °C yields a poorly crystallized solid state cluster, [W₆Cl₈]Cl₂Cl_4/2, which exhibits catalytic activity for the dehydration of ethanol to yield ethylene and a small amount of ethyl ether and acetal. The activity is attributed to the Br?nsted acidity of the hydroxo ligand that is produced by elimination of hydrogen chloride from the chloro and aqua ligands. The catalytic activity increases with increasing temperature, and reaches a maximum at 300 °C. The catalytic activity then disappears above 350 °C, at which temperature the crystallinity of the cluster improves and the active sites are included in the crystal. In the case of primary alcohols, the reactivity decreases with increasing length of the carbon chain, and secondary alcohols are more reactive than the corresponding primary alcohols. Halide clusters of niobium, molybdenum, and tantalum having the same metal framework are also active catalysts for these reactions.     

硫氰酸钨(V)络合物稳定常数的测定

测定了水溶液中硫氰酸钨(V)络合物的吸收光谱,最大吸收波长为405 nm。在盐酸浓度为3.56 mol/L、离子强度为0.088 mol/L的溶液中,硫氰酸钾溶液浓度在0.018～0.088 mol/L范围内,与硫氰酸钨(V)络合物的平均摩尔吸光系数Δε呈函数关系。测得络合物的络合比为1:4。计算出络合物的各级累积稳定常数和摩尔吸光系数分别为:β_1=40.73,β_2=1.10×10~3,β_3=2.40×10~4,β_4=4.16×10~5,Δε_1=9.33×10~3,Δε_2=9.64×10~3,Δε_3=9.93×10~3,Δε_4=1.10×10~4(t=17.7℃)。     

Redox reactions of GeII and SnII dihalides with triethylsilane and triethylgermane

Dihalogermylenes, dihalostannylenes, and their complexes (EI₂, ECl₂·dioxane, and (CO)₅W=ECl₂·THF, where E = Ge or Sn), unlike organylgermylenes, are not inserted at the Si—H (Ge—H) bond of triethylsilane (triethylgermane). The reactions of SnI₂, ECl₂·dioxane, and (CO)₅W=ECl₂·THF (E = Ge or Sn) with Et3E"H (E" = Si or Ge) occur as redox processes. Depending on the nature of the reagents, the reactions afford products of oxidative coupling (Et₃SiSiEt₃) and/or haloiodination (Et₃SiX and Et₃GeX) of triethylsilane (triethylgermane). The proposed mechanism of these reactions involves the electron transfer to form radical-ion pairs.     

光照下n-InP/溶液界面击穿过程的研究

In this work, the tunneling breakdown of n-InP electrode using large signal current density step has been investigated. The influence of current density on the tunneling breakdown is not obvious, but the light intensities affect the breakdown severely. Some parameters are calculated during breakown and explained.     

n-InP在Fe~(3+)/Fe~(2+)溶液中光脉冲暂态行为研究

本文应用光脉冲技术研究了电极电位及电流对n-InP在Fe~(3+)/Fe~(2+)溶液中暂态行为的影响。结果表明,响应峰值处的规律与稳态相似,电位及电流对衰减影响可用逆扩散机理来解释,光强变化对衰减无影响。实验中还发现响应衰减过程有过冲现象。最后讨论了光强及电极电位对输出电量的影响。     

Partial thermal reduction of ammonium paratungstate tetrahydrate

Thermal decomposition of ammonium paratungstate tetrahydrate, (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O has been followed by simultaneous TG/DTA and online evolved gas analysis (TG/DTA-MS) in flowing 10% H₂/Ar directly up to 900°C. Solid intermediate products have been structurally evaluated by FTIR spectroscopy and powder X-ray diffraction (XRD). A previously unexplained exothermic heat effect has been detected at 700–750°C. On the basis of TG/DTA as well as H₂O and NH₃ evolution curves and XRD patterns, it has been assigned to the formation and crystallization heat of γ-tungsten-oxide (WO_2.72/W₁₈O₄₉) from β-tungsten-oxide (WO_2.9/W₂₀O₅₈) and residual ammonium tungsten bronze.     

Synthesis, Structure, and Properties of the Cyclic Mixed Valence Oxothiotungstate [W8S8O8(OH)8(H3WO6]2−

The novel polyoxothioanion [W₈S₈O₈(OH)₈(H₃WO₆]^2– was prepared by acido-basic condensation of four [W₂S₂O₂]²⁺ thiofragments in the presence of tungstate ion. Rb₃[W₈S₈O₈(OH)₈(H₃WO₆]13H₂O was isolated in the solid state and fully characterized by X-ray diffraction study (monoclinic, C2/m [a=20.3540(1) Å; b=11.8042(2) Å; c=13.9355(2) Å; =90°; =131.134(1)°; =90°]. The molecular structure consists of an octameric {W₈S₈O₈(OH)₈} wheel encapsulating a central octahedron {H₃WO₆}^3–. The packing reveals a remarkable 3-D array resulting from connections between Rb⁺ and octameric wheels. The Rb⁺ cations form infinite parallel chains, which are mutually connected by the cyclic oxothioanions. The compound was also characterized by infrared spectroscopy and elemental analysis.     

Cu/WO3-NiO上光促表面催化二氧化碳与水合成甲醇反应的规律

 采用溶胶－凝胶法制备了n－p复合半导体材料0．75％Cu／WO3－1．5％NiO，用X射线衍射、透射电镜、红外光谱、紫外－可见光漫反射和程序升温脱附等技术对材料结构、吸光性能和化学吸附性能进行了表征，研究了该材料对CO2与H2O合成CH3OH的光促表面催化反应(PSSR）规律．结果表明：所制备的材料明显有利于促进目的反应，室温条件下就有CH3OH生成，选择性超过90％，升高反应温度可提高CH3OH产量，且选择性仍高于88％．根据实验结果，得出CO2在材料表面的卧式吸附态为CH3OH的前驱物，并对PSSR机理进行了讨论．     

Chemical Processing of Potassium Substituted (Pb0.6Ba0.4)Nb2O6 Powders and Thin Films Through Metallo-Organics

Highly oriented tungsten bronze K_0.4(Pb_0.6Ba_0.4)_0.8Nb₂O₆ ferroelectric thin films have been prepared from metal alkoxides and metal acetate by chemical process. The formation of solid solution with potassium was found to be very effective to form the tungsten bronze phase at lower temperatures compared with (Pb_0.6Ba_0.4)Nb₂O₆. The amount of potassium in the composition of K_x(Pb_0.6Ba_0.4)_{1 – x/2}Nb₂O₆ [0 x 0.4] is also important to crystallize in the tungsten bronze phase. K_0.4(Pb_0.6Ba_0.4)_0.8Nb₂O₆ films with c-axis preferred orientation were successfully synthesized on MgO(1 0 0) and Pt(1 0 0)/MgO(1 0 0) substrates above 700°C. KPBN60 thin film on Pt(1 0 0)/MgO(1 0 0) showed a remnant polarization of 20 C/cm² and a coercive field of 140 kV/cm at –150°C.