甲醇液相氧化羰基化合成碳酸二甲酯催化剂研究进展

甲醇液相氧化羰基化合成碳酸二甲酯（DMC）的催化体系目前主要有铜系、钴系、钯铜复合系以及硒系四种。铜系中CuCl催化体系已工业化,但由于氯离子的丢失而引起催化剂活性的下降及设备腐蚀问题是其致命缺点。这一问题可采取添加配体或助剂稳定氯离子或取代氯离子等方法来解决。其中后者是一种较新的方法,有较好的工业应用前景。     

Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide over Metal-Doped Titanium Oxides

Various metal-doped (Fe, V, Zr, Mg) titanium oxides were prepared by an acid-catalyzed sol–gel method and their properties as catalysts were investigated for oxidative dehydrogenation of ethylbenzene in the presence of carbon dioxide. The characterization techniques, XRD, BET, TGA were employed to analyze the features of catalyst. Fe₃Ti catalyst was found to be quite effective among the catalysts tested at 823 K, 39.8% ethylbenzene conversion and 98% styrene selectivity were acquired.     

Strain engineering for thermal conductivity of single-walled carbon nanotube forests

We perform classical molecular dynamics simulations to investigate the mechanical compression effect on the thermal conductivity of the single-walled carbon nanotube (SWCNT) forest, in which SWCNTs are closely aligned and parallel with each other. We find that the thermal conductivity can be linearly enhanced by increasing compression before the buckling of SWCNT forests, but the thermal conductivity decreases quickly with further increasing compression after the forest is buckled. Our phonon mode analysis reveals that, before buckling, the smoothness of the inter-tube interface is maintained during compression, and the inter-tube van der Waals interaction is strengthened by the compression. Consequently, the twisting-like mode (good heat carrier) is well preserved and its group velocity is increased by increasing compression, resulting in the enhancement of the thermal conductivity. The buckling phenomenon changes the circular cross section of the SWCNT into ellipse, which causes effective roughness at the inter-tube interface for the twisting motion. As a result, in ellipse SWCNTs, the radial breathing mode (poor heat carrier) becomes the most favorable motion instead of the twisting-like mode and the group velocity of the twisting-like mode drops considerably, both of which lead to the quick decrease of the thermal conductivity with further increasing compression after buckling.     

A size-dependent thermodynamic model for coke crystallites: The carbon–hydrogen system up to 2500 K

The development is presented of a model of the thermodynamic functions of enthalpy, entropy and Gibbs energy for the elements carbon and hydrogen in coke crystallites. It is applicable to varying degrees of graphitization, described by the crystallite length L_a and the crystallite height L_c. The model parameters are derived from known properties such as bond enthalpies and entropies of formation. Good agreement has been obtained between the predicted thermal dehydrogenation of petroleum cokes and experimental data. The removal of hydrogen from idealized coke crystallites is predicted to occur mostly between 1100 and 1300 K. Agreement has also been found in the comparison of the predicted thermodynamic stability of coke relative to graphite, in a previous experimental study. This stability has been determined as at ≈900 J g⁻¹ at temperatures between 950 and 1250 K and for L_a = 10 nm. The current predictive capacity of the present model is valid for temperatures up to 2500 K.     

A study of CVD diamond deposition on cemented carbide ball-end milling tools with high cobalt content using amorphous ceramic interlayers

In this paper, CVD diamond coatings are deposited on cemented carbides with 10 wt.% Co using amorphous SiO₂ and amorphous SiC interlayers. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectrum and X-ray diffraction (XRD) are carried out to characterize the microstructure and composition of as-deposited films. Moreover, the adhesion and cutting performance of as-fabricated diamond coatings are studied. Indentation tests show that the amorphous ceramic interlayers can enhance the adhesion between diamond films and WC–Co substrates. The cutting tests against zirconia indicate that the tools with amorphous ceramic interlayered diamond coatings exhibit improved cutting performance. The amorphous ceramic interlayers can improve the adhesive strength and wear endurance of diamond coatings on WC–10 wt.% Co substrates, which provide a viable way for adherent diamond coatings on cemented carbide tools with high cobalt content.     

Effect of methanol addition on higher alcohol synthesis over modified molybdenum sulfide catalysts

One of the main problems in higher alcohol synthesis is the poor product distribution. Cofeeding of methanol, together with the synthesis gas, has been suggested in order to increase the yield of ethanol and higher alcohols. In this work, the effect of methanol addition on K–MoS₂ and K–Ni–MoS₂ catalysts was studied at 71 bar, 340 °C and GHSV = 6000 N mL/h · g_catalyst. Under these conditions methanol recycle is not a viable option for boosting higher alcohol production. The main result was an increase in methane yield, while the effect in higher alcohols was negative or not significant.     

Dimethyl carbonate synthesis from methyl nitrite and CO over activated carbon supported Wacker-type catalysts: The surface chemistry of activated carbon

A series of supported Wacker-type catalysts under treatment of nitric acid were prepared and utilized in the synthesis of dimethyl carbonate from CO and methyl nitrite. Nitrogen adsorption, Boehm titration, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and H₂-temperature-programmed reduction (H₂-TPR) were employed to explore the relationship between the physicochemical properties and reactivity of catalysts. Correlated with the results of Boehm titration, it was found that catalytic activities increased monotonically with the number of phenolic group on activated carbon surface. XPS spectra showed that the catalysts, which had much more amount of phenolic group, were possessed of large amount of Cu^2 + species. H₂-TPR results indicated that the phenolic group contributed to the easier reducibility of Cu^2 + species, further facilitating the oxidation cycle between Pd and Cu species and consequently the catalytic performance.     

CO2和甲醇直接合成碳酸二甲酯耦合脱水体系研究进展

二氧化碳和甲醇直接合成碳酸二甲酯反应受热力学平衡限制,导致反应物转化率和产物收率较低,极大地阻碍了其工业化应用。耦合脱水体系能够将反应过程中产生的水及时脱除,促进反应正向进行,进而提高产物碳酸二甲酯收率。根据耦合脱水的原理不同,主要可分为物理耦合脱水和化学耦合脱水。本文综合分析了近年来应用于该反应不同物理脱水工艺和化学脱水剂的研究进展,详细论述了不同脱水体系的脱水原理和对反应的促进作用,并对不同脱水体系的优点及局限进行了归纳和分析,提出通过优化反应工艺或设计新的反应工艺大幅降低反应体系的能耗,同时探索更加廉价、低毒且易循环利用的化学脱水剂是耦合脱水体系今后的主要发展趋势。     

基于载波移相技术的静止无功发生器的研究

为了扩大静止无功发生器的补偿容量和减少交流侧的输出谐波,本文采用了级联多电平的主电路结构,并使用了载波移相技术的方法对其进行调制;最后在Matlab上搭建了基于载波移相技术的静止无功发生器的仿真,仿真结果表明采用载波移相调制方法谐波输出含量少,整个系统也能很好的补偿系统的无功电流。     

基于SVPWM串联有源电力滤波器控制策略的实现

针对三相电网中谐波的影响,本文介绍了串联有源电力滤波器的结构及其补偿特性。在有源电力滤波器补偿控制方式上,采用空间电压矢量SVPWM的控制技术,克服了传统控制方式动态响应速度慢、开关频率波动大的缺点,使整个补偿系统开关频率恒定,补偿精度高且动态响应快。