Oxidative dehydrogenation of isobutane over magnesium molybdate catalysts

A series of Mo-Mg-O catalysts with different crystalline phases (pure and mixtures) have been studied in the oxidative dehydrogenation of isobutane. X-ray diffraction, UV–Vis spectroscopy and temperature programmed reduction were applied to characterise the samples. In addition, the kinetics of the lattice oxygen exchange with labelled C¹⁸O₂ was measured for all samples. It has been found that the MgMoO₄ phase contains the surface active sites suitable for the adsorption of isobutane and for its dehydrogenation to isobutene with the minimum of cracking reaction. Moreover, for this reaction the migration of lattice oxygen ions is not a key parameter in the control of the catalytic properties of these materials.     

丁烯氧化脱氢制丁二烯体系的热力学计算与分析

计算了正丁烯氧化脱氢制丁二烯体系中各反应的标准摩尔反应焓、标准摩尔吉布斯自由能、平衡常数,并利用Gibbs自由能最小法计算了反应体系的热力学平衡组成。结果表明,正丁烯的氧化脱氢与完全氧化反应在热力学上均可完全进行,但是丁二烯的产率受热力学平衡限制。因此,提高丁二烯产率的关键在于开发高性能的催化剂,从动力学上角度充分抑制COx的生成反应。     

丁烯氧化脱氢铁系催化剂绿色制备关键因素的考察

丁烯氧化脱氢是工业生产丁二烯常用的工艺,其中,铁系催化剂是丁烯氧化脱氢工业使用的主流催化剂,为满足清洁生产的需要,了解催化剂制备过程中产生的NOx及废水等排放物的组成尤为重要。对铁系催化剂生产过程中前驱体制备步骤的气体生成及组成进行研究,同时对沉淀洗涤步骤产生的废液成分进行检测。通过XRD、TG-DSC、ICP和TPC等技术对催化剂性质及制备排放物进行分析,考察制备条件对催化剂结构和性能的影响及废物排放的变化规律。结果表明,在前驱体制备溶铁过程中,空气气氛下提高硝酸浓度可有效抑制氢气的产生;不同焙烧温度阶段,生成NOx种类有较大差别;排放废水中含有较多的Zn离子。焙烧条件试验表明,最佳焙烧温度为(650~700)℃,焙烧时间低于9 h。     

Transition Metal‐Free Carbazole Synthesis from Arylureas and Cyclohexanones

An efficient strategy for carbazole synthesis from arylureas and cyclohexanones under transition metal‐free conditions has been developed. The combined use of potassium iodide and iodine could significantly improve the reaction efficiency to provide 2,6‐disubstituted 9‐arylcarbazoles in moderate to good yields. In this kind of transformation, the whole carbazole moiety (except the nitrogen atom) comes from two equivalents of cyclohexanones.

     

碳材料在多相催化过程中的应用

碳是自然界中存在最为广泛的元素,具有丰富的结构和形态。碳材料不仅可以作为理想的催化剂载体,其本身也表现出对多种催化过程的优异性能。综述了碳材料在化学品制造、环境催化与能源催化等领域的最近研究进展,并总结了碳材料在这些过程中的催化作用机理。     

Oxidative dehydrogenation of propane in a perovskite membrane reactor with multi‐step oxygen insertion

A membrane reactor incorporating a hollow fiber with successive parts of oxygen permeable and passivated surface segments has been developed and was used for the oxidative dehydrogenation (DH) of propane. This membrane geometry allows a controlled oxygen feeding into the reactor over its axial length. In the oxidative DH, the thermodynamic limitation of propane DH can be overcome. By using this novel hollow fiber membrane reactor with a Pt/Sn/K DH catalyst, oxygen separation and propene formation could be established even at temperatures as low as 625°C with long‐term stability. Combining the hollow fiber membrane and the DH catalyst, the highest propene selectivity of 75% was observed at a propane conversion of 26% and 625°C whereas the best propene yield of 36% was obtained at 675°C (48% propene selectivity). The performance of this reactor is evaluated by applying various reaction conditions. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

固定床乙苯脱氢制苯乙烯工艺条件的研究

采用固定床反应器,在自制铁系催化剂的作用下,研究了乙苯脱氢制苯乙烯反应的工艺条件,应用气相色谱技术测定了不同工艺条件下的产物组成。结果表明,影响乙苯脱氢制苯乙烯反应的主要因素有反应温度、水与乙苯物质的量比及催化剂活性。反应温度的影响最为显著,当反应温度较低时,催化剂活性较低,产物平衡组成中苯乙烯含量低、未反应的乙苯含量高;当反应温度过高时,系列副反应加剧,催化剂表面结焦倾向加大,导致催化剂活性明显下降。确定了最佳的反应条件为:水与乙苯物质的量比(8~15)∶1、反应温度580~590℃。在此条件下,乙苯的转化率为89.29%、苯乙烯收率为64.59%、苯乙烯选择性为72.34%。     

Surface phase transformation of ZrO2 in VOx/ZrO2 catalysts for boosting propane nonoxidative dehydrogenation

The nanocatalysts of VO_x deposited on ZrO₂ supports with single monoclinic (ZrO₂-M), tetragonal (ZrO₂-T), and binary monoclinic-tetragonal (ZrO₂-MT) phase were synthesized. VO_x/ZrO₂-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VO_x/ZrO₂-M and VO_x/ZrO₂-T catalysts. Among VO_x/ZrO₂-MT catalysts, the conversion and deactivation rate constant of VO_x/ZrO₂-M₃₁T₆₉ catalyst is 35.2% and 0.22 h⁻¹, respectively. The promoting role of ZrO₂-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VO_x/ZrO₂-MT catalyst improves the structural properties and dispersion of VO_x. The tetragonal-monoclinic transformation on the ZrO₂-MT surface facilitates VO_x reduction and produces additional V³⁺ active sites. The highly dispersed V³⁺ sites on the ZrO₂-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO₂-MT is expected to obtain high-efficient catalysts further.     

Ce2Mg17及其氢化物添加剂对LiBH4的放氢作用机理研究

为改善LiBH4体系的可逆吸放氢性能,将Ce2Mg17合金(简称为CM)及其氢化物(CeH2.51和MgH2,简称为CMH)分别与LiBH4球磨4 h制得LiBH4-0.02CM和LiBH4-0.02CMH复合储氢体系,采用MS、TPD、XRD和FT-IR等测试手段研究了不同状态Ce-Mg添加剂对复合储氢体系可逆吸放氢性能的影响及其作用机制。结果表明:Ce2Mg17合金本身对改善LiBH4吸放氢性能没有明显作用;而Ce2Mg17氢化物(即MgH2和CeH2.51)可降低复合体系中LiBH4的放氢温度和提高LiBH4的放氢速率,并可明显改善体系的可逆吸放氢性能。进一步分析表明,MgH2和CeH2.51对LiBH4的协同改性作用是有效降低LiBH4热力学稳定性、提高LiBH4-Ce-Mg复合体系可逆吸放氢性能的主要原因。     

Carbon supports for the catalytic dehydrogenation of liquid organic hydrides as hydrogen storage and delivery system

The use of liquid organic hydrides as hydrogen carriers is a promising storage and delivery system due to the advantages of using liquid-based infrastructures and its economic feasibility compared to other conventional systems. The reversible dehydrogenation/hydrogenation of liquid organic hydrides is a key point for the development of highly performance reactors. In this study different carbon materials have been investigated as platinum supports, including carbon nanofibers, carbon black, carbon xerogel, activated carbon and ordered mesoporous carbon. To individuate the effect of the carbon support on the catalytic activity, platinum particles were synthesized by a microemulsion procedure. The analysis of the hydrogen evolution curves indicate that the support BET surface area plays a very important role on the initial catalytic activity, obtaining a maximum rate of 220 mmol g_Pt⁻¹ min⁻¹ when using an ordered mesoporous carbon with a surface area of 930 m² g⁻¹. Nevertheless, the analysis of catalytic activity at prolonged duration indicates a better behavior toward deactivation for supports characterized by wide pores and low graphitization degree like carbon black or carbon xerogel, despite their lower initial dehydrogenation rate (100–140 mmol g_Pt⁻¹ min⁻¹). The ultimate use in the dehydrogenation reactor as well as the operation conditions will define the best catalyst structure from the point of view of the carbon support.