Cyclohexene dehydrogenation and hydrogenation on Pt(111) monitored by SFG surface vibrational spectroscopy: different reaction mechanisms at high pressures and in vacuum

The hydrogenation and dehydrogenation reactions of cyclohexene on Pt(111) crystal surfaces were investigated by surface vibrational spectroscopy via sum frequency generation (SFG) both under vacuum and high pressure conditions with 10 Torr cyclohexene and various hydrogen pressures from 30 up to ~600 Torr. At high pressures, the gas composition and turnover rate (TOR) were measured by gas chromatography. In vacuum, cyclohexene on Pt(111) undergoes a change from π/σ‐bonded, σ‐bonded cyclohexene and c‐C₆H₉ surface species to adsorbed benzene when the surface was heated from 130 to 330 K. A site‐blocking effect was observed at saturation coverage of cyclohexene that caused dehydrogenation to shift to somewhat higher surface temperature. At high pressures, however, none of the species observed in vacuum conditions were detectable. 1,4‐cyclohexadiene (1,4‐CHD) was found to be the major species on the surface at 295 K, even with the presence of nearly 600 Torr of hydrogen. Hydrogenation was the only detectable reaction at the temperature range between 300 and 400 K with 1,3‐cyclohexadiene (1,3‐CHD) on the surface, as revealed by SFG. Further increasing the surface temperature results in a decrease in hydrogenation reaction rate and an increase in dehydrogenation reaction rate and both 1,3‐CHD and 1,4‐CHD were present on the surface simultaneously. The simultaneous observation of the reaction kinetic data and the chemical nature of surface species allows us to postulate a reaction mechanism at high pressures: cyclohexene hydrogenates to cyclohexane via a 1,3‐CHD intermediate and dehydrogenates to benzene through both 1,4‐CHD and 1,3‐CHD intermediates. Isomerisation of the 1,4‐CHD and 1,3‐CHD surface species is negligible. This revised version was published online in July 2006 with corrections to the Cover Date.     

硫酸锆硫酸氢钾催化合成环己烯研究

用硫酸锆、硫酸氢钾分别代替浓硫酸,催化环己醇脱水合成了环己烯,主要考察了催化剂用量、分馏反应时间对产物收率的影响。结果表明,硫酸锆、硫酸氢钾催化效果好,最佳用量为环己醇质量的15％;其中硫酸锆催化效果更好,在最佳用量下,分馏反应60min,产物收率可达68．29％,且催化剂的重复使用性能较好。硫酸锆、硫酸氢钾用作合成环己烯的催化剂符合清洁生产的要求。     

苯部分加氢制环己烯的钌系催化剂研究新进展

评述了催化剂的制备条件、助催化剂的选择、添加剂的筛选等因素对催化剂活性的影响,指出添加无机盐和水有利于提高环己烯的选择性．讨论了反应温度、搅拌速度、氢气压力的影响,相应的最适宜条件范围为：温度３６０ ～４６０ Ｋ,压力４ ．０ ～５ ．０ ＭＰａ,搅拌转速１５００ ｒ／ｍｉｎ．探讨了苯部分加氢制环己烯的反应机理及加氢初始动力学方程,并对沉淀钌黑催化剂活性进行评价,在温度４１３ Ｋ,压力５．０ ＭＰａ下,苯的转化率为９６ ．４７ ％ ,环己烯的选择性达５０ ．０１％ ,其催化活性及选择性可满足工业化的要求．     

对甲苯磺酸催化合成环己烯

以对甲苯磺酸作催化剂,对环己醇脱水制备环己烯的反应进行研究。考察了影响反应的因素,得出了其最佳的反应条件为:催化剂用量为环己醇质量的4%,反应时间1h,产品收率可达91.90%。     

Polymer‐bound schiff‐base complex catalyst for effective oxidation of olefins with molecular oxygen

Polymer‐bound Schiff‐base ligand (PS–SalPhe) was prepared from polystyrene‐bound salicylaldehyde and phenylalanine, and its complex (PS–SalPhe–M) (M = Co, Mn) was also synthesized. The polymer ligand and its complex were characterized by infrared spectra, small area X‐ray photoelectron spectroscopy, and ICP–AES. In the presence of the complex, cyclohexene can be effectively oxidized by molecular oxygen without a reductant. The major products of the reaction are 2‐cyclohexen‐1‐ol (—OH), 2‐cyclohexen‐1‐one (CO), and 2‐cyclohexen‐1‐hydroperoxide (—OOH ), which is different from the typical oxidation of cyclohexene. The mechanism of cyclohexene oxidation is also discussed. Long‐chain linear aliphatic olefins, such as 1‐octene, 1‐decene, 1‐dodecene, and 1‐tetradecene, can be directly oxidized by molecular oxygen catalyzed by PS–SalPhe–M (M = Mn, Co), which yields the 1,2‐epoxy alkane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1138–1143, 2000     

Hydrogenation of olefins over palladium(II) complexes supported on a modified macroporous polymer bead

Gellular and macroporous polymer supports have been prepared. A modified polymer support has also been prepared by coating the internal pore wall of macroporous poly(styrene-co-divinylbenzene) with lightly crosslinked polymer containing functional groups. The supports were phosphinated and PdCl₂ was supported on them. The supports and catalysts were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The polymer-supported Pd catalysts were used in the hydrogenation of olefins. The effects of the support structure and solvent were also studied. ©1997 SCI     

Liquid-Phase Hydrogenation of Benzene to Cyclohexene Using Ruthenium-Based Heterogeneous Catalyst

Selective hydrogenation of benzene to cyclohexene has been studied in a high pressure slurry reactor using supported ruthenium catalysts. The organic base monoethanolamine (MEA) was found to give better selectivities than the conventional inorganic salt additive (zinc sulphate). Parameters studied were the effects of various supports such as alumina, silica, titania, zirconia, niobium oxide, etc., benzene to water ratio, catalyst weight, and presence of cyclohexane in the feed. Reusability of the catalyst was also studied. © 1997 SCI.     

Recovery and Recycling of Ti Supported Bimodal Mesoporous Catalysts Prepared via Ship-in-a-bottle Method in the Epoxidation of Cyclohexene

Ti/BMMs (Ti supported bimodal mesoporous silica) catalysts have been prepared via self-assembly route com-bined with ship-in-a-bottle method. The recovery and recycling performances of Ti/BMMs were inv...     

S2 O2 -8/ZrO2-WO3复合固体超强酸的制备和表征及其催化合成环己烯的性能

通过沉淀浸渍法制备了S2O2 -8/ZrO2-WO3复合固体超强酸催化剂,采用Hammett指示剂法、FTIR、XRD和BET等手段对其进行了表征;以环己醇液相脱水制备环己烯为探针反应,通过正交实验优化了S2O2 -8/ZrO2-WO3催化剂的制备条件和反应条件.实验结果表明,在w(H2WO4)=10.0%(基于Zr(OH)4粉末)、(NH4)2S2O8溶液浓度为0.75 mol/L、浸渍时间为18 h、焙烧温度为550 ℃的条件下制备的S2O2 -8/ZrO2-WO3催化剂表现出良好的催化性能;采用该催化剂制备环己烯的优化反应条件为:催化剂用量为环己醇质量的2.77%、反应温度为180～185 ℃、反应时间为60 min,在此条件下环己烯平均收率可达96.57%.该工艺具有绿色、安全、操作简单和收率高等优点.     

环己烯水合过程汽-液两相流动的CFD研究

环己烯直接水合是制备环己醇的一种新工艺,本文利用体积率函数法（VOF法）建立了环己烯水合流动过程的数学模型,考虑了汽-液相间摩擦力动量源项、表面张力动量源项和多孔介质动量源项,定量描述了汽-液两相逆流流动过程。根据计算流体力学（CFD）模型模拟了黏度、表面张力和流动阻力对流动的影响,结果表明黏度和表面张力影响液膜厚度和液面波动程度,进而影响传质;流动阻力过大会导致液膜断裂,不利于传质。