Titania–silica epoxidation catalysts modified by mono- and bidentate organic functional groups

Amorphous, mesoporous titania–silica mixed oxides with covalently bound mono- and bidentate acetoxyalkyl and aminoalkyl functional groups were prepared using the solution sol–gel process and ensuing low temperature supercritical extraction with CO₂. Titanbisacetylace-tonatediisopropoxide, tetramethoxysilane and amino- or acetoxyalkyl-trimethoxysilane precursors were used for the syntheses of hybrid aerogels with a constant Ti:Si atomic ratio of 1:12. The mixed oxides were characterized by thermal analysis, N₂physisorption, ¹³C- and ²⁹Si-CP-MAS NMR spectroscopy, and electron microscopy. The amorphous mesoporous structure of the aerogels depended markedly on the nature of the modifier. Organic modification enhanced remarkably the rate of epoxidation of cyclohexene and cyclohexenol. The highest selectivity in the more demanding epoxidation of cyclohexenol, 91% at 80% TBHP conversion, was achieved with a bidentate (diaminoalkyl)-modified aerogel.     

Hydrophobic titania–silica aerogels: epoxidation of cyclic compounds

Topics in Catalysis - Titania–silica mixed oxides with covalently bound methyl or phenyl groups were prepared from the corresponding alkyltrimethoxysilane and tetramethoxysilane using a...     

Titania–silica epoxidation catalysts modified by acetoxypropyl groups

Mesoporous titania–silica aerogels with TiO₂SiO₂ = 1:9 weight ratio and varying amounts of covalently bound 3‐acetoxypropyl groups were prepared from 3‐acetoxypropyltrimethoxysilane, tetramethoxysilane and titanbisacetylacetonatdiisopropoxide. The textural properties of the hybrid aerogels were strongly influenced by the concentration of acetoxypropyl groups. The BET surface area and specific pore volume were significantly lowered upon introduction of the polar organic modification. Despite these less favorable textural properties, all modified aerogels were remarkably more active epoxidation catalysts, and in the epoxidation of cyclohexenol also more selective, than the unmodified titania–silica aerogel. For example, incorporation of only 2 mol% acetoxypropyl groups lowered the BET surface area from 813 to 339 m² g^-1, whereas the selectivity to 2,3‐epoxy‐cyclohexenol increased from 76 to 90%, and the reaction time (required to achieve 70% TBHP conversion) decreased from 46 to 5 min. The higher epoxide selectivity and the small enhancement in cis/trans ratio in the epoxide may indicate an electron pair donor interaction between the ester carbonyl group and the Ti active site. This revised version was published online in July 2006 with corrections to the Cover Date.     

烯烃不对称环氧化反应催化剂的研究进展

综述了手性催化剂催化的不对称环氧化反应研究进展情况。     

Catalytic Asymmetric Epoxidation of 2‐Cyclopentenones

The first highly efficient asymmetric epoxidation of 2‐cyclopentenones has been developed. Using a newly designed and readily available Cinchona amine catalyst, 2‐cyclopentenones are reacted with hydrogen peroxide to give the corresponding epoxycyclopentanones in high yields and excellent enantioselectivities.     

Epoxidation of Propylene over Ag-CuCl Catalysts Using Air as the Oxidant

Ag-CuCl catalysts were found to be active and selective for the epoxidation of propylene using air as the oxidant. Ag catalyst gives a propylene conversion of 31.6%, with a propylene oxide (PO) selectivity of 0.42% at a reaction temperature of 350 °C after 220 min of reaction. Addition of CuCl significantly improves the selectivity to PO, and suppresses the conversion of propylene. The Ag-CuCl (1/0.6) catalyst gives propylene conversion of about 3% and a PO selectivity of about 30% at a reaction temperature of 350 °C after 500 min of reaction. The activity of the Ag-CuCl catalyst increases with the reaction time and the selectivity to PO is very stable for this catalyst. It is found that AgCl and CuO phases formed during the catalyst preparation are beneficial to the epoxidation of propylene.     

苯乙烯环氧化反应分子筛催化剂研究进展

综述了苯乙烯环氧化制取环氧苯乙烷的几种分子筛／H2O2催化体系，介绍了微孔分子筛（TS-1）、Ti-ZSM-5和Ti-ZSM-11分子筛介孔分子筛（MCM-41），β-钛硅分子筛、负载金属配合物的中孔分子筛及其在苯乙烯环氧化反应中的性能。     

合成磷霉素的环氧化催化剂的研究

采用原位法制备活性炭负载磷钨酸催化剂,在制备催化剂过程中加入修饰剂,获得活性炭负载修饰型PW/C催化剂,并用于顺丙烯磷酸的环氧化反应.结果表明,加入质量分数5%的修饰剂可以使该催化剂环氧化收率明显提高,重复使用稳定性也明显改善.采用BET、IR和XRD方法表征证明,在活性炭负载催化剂上主要催化活性成分为H3PW12O4...     

杂多酸催化烯烃环氧化的研究进展

烯烃的环氧化物是应用最广泛的有机中间体,在有机合成反应中烯烃的环氧化反应占有十分重要位置。本文主要论述了以杂多酸作为催化剂,季铵盐作为相转移催化剂,以双氧水为氧化剂,在两相条件下催化烯烃环氧化的反应过程。     

烯烃环氧化钼系催化剂的多相化研究进展

介绍了以有机聚合物和无机硅酸盐为载体，负载钼催化剂及其对烯烃环氧化反应催化性能的研究进展；分析了硼酸树脂、乙烯-丙烯橡胶、螯合树脂、苯并吡咯树脂、聚酰亚胺树脂、聚硅氧烷树脂、阳离子交换树脂和聚苯乙烯等有机聚合物为载体的研究情况；评价了以无机硅酸盐为载体，采用溶胶-凝胶、离子交换、同晶取代等方法负载钼对催化性能的影响；展望了多相化烯烃环氧化钼系催化剂的发展前景。     

氯丙烯催化环氧化钛催化剂研究进展

主要介绍了TiO2／SiO2、TS-1及其改性的TS-1等催化剂催化氯丙烯直接环氧化制备环氧氯丙烷的近期研究进展，对各方法的特点和发展前景进行了讨论，并指出了氯丙烯直接环氧化制备环氧氯丙烷的难点和发展趋势。     

金催化剂在丙烯气相直接环氧化反应中的应用

环氧丙烷（PO）是一种重要的有机化工原料。近来发现采用沉积-沉淀法将金高度分散在一些含钛物质表面上时,能够催化H2-O2-丙烯气相体系直接合成PO。金粒大小和分散状态,载体及助剂等因素对催化剂性能有重要影响。主要就催化剂性能的影响因素,反应及失活机理等方面的研究进展情况进行了总结和评述,以利于将来深入地研究。     

A Simple and Convenient Method for Epoxidation of Olefins without Metal Catalysts

An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non‐activated olefins give epoxides in high yields and good selectivity at ambient conditions.     

Adsorption and degradation of the cationic dyes over Co doped amorphous mesoporous titania–silica catalyst under UV and visible light irradiation

Cobalt doped amorphous mesoporous titania–silica with Ti/Si mass ratio of 0.8 (Co–TiO₂–SiO₂) was synthesized and used for the photodegradation of six cationic dyes (gentian violet, methyl violet, methylene blue, fuchsin basic, safranine T, and Rhdamine B) under UV and visible light illumination. The catalyst was characterized by a combination of various physicochemical techniques, such as N₂ physisorption, diffuse reflectance UV–vis, X-ray diffraction, and FT-IR.Co–TiO₂–SiO₂ exhibited activity under UV light and had better activity under visible light when compared with that of Degussa P25 TiO₂. The activity of Co–TiO₂–SiO₂ was also compared with that of Co-MCM-41, Co doped mesoporous titania with a crystalline framework (Co–MTiO₂) and titania-loaded Co doped MCM-41 (TiO₂/Co-MCM-41) for the degradation of gentian violet under visible light irradiation. It was also found that the degradation rates of Co–TiO₂–SiO₂ for gentian violet, methyl violet, methylene blue, fuchsin basic and safranine T were greater in alkaline media than in acid and neutral media, while it did not exhibit any significant activity for the photodegradation of Rhdamine B in alkaline media or in acid media under visible light irradiation.     

Preparation of Titanium-Containing Carbon–Silica Composite Catalysts and Their Liquid-Phase Epoxidation Activity

Titanium-containing catalysts have been prepared by two different post-synthesis methods using activated carbon and carbon-silica composite as catalyst supports. They have been applied to the liquid-phase epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) and H₂O₂. The carbon-silica composite catalyst showed a high conversion and selectivity to epoxide compared to the Ti-carbon catalyst and silica-based catalysts for the cyclohexene epoxidation with H₂O₂. The highest values of cyclohexene conversion and epoxide selectivity were obtained with the carbon-silica composite catalyst having a titanium content of 3 wt%.     

SiO2负载钴系催化剂的环己烯环氧化性能

采用沉积沉淀法制备不同负载量的SiO₂（硅胶）负载钴氧化物催化剂,采用X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电镜（TEM）、N₂吸脱附等手段对催化剂进行表征,结果表明钴系氧化物为Co₃O₄,并且钴氧化物均匀地负载在SiO₂（硅胶）载体上,其活性组分的粒子大小集中分布在2～10nm。将制备的催化剂应用于环己烯环氧化反应,以环己烯、分子氧为原料,异丁醛为催化助剂,N,N-二甲基甲酰胺（DMF）为反应溶剂,在高压釜中进行。同时将SiO₂负载钴氧化物催化剂与不同载体上制备的钴系催化剂进行比较,发现催化剂用量0.20g、环己烯2.00g、异丁醛3.50g、反应温度50℃、反应时间5h、氧气压力4MPa时,环己烯的转化率和环氧环己烷的选择性分别可达到66.56%和71.03%。     

Nonsupercritical synthesis of microporous gels

In this work, the development of microporous gels using a novel degradation process not involving supercritical fluids is proposed. Photosensitive organic–inorganic hybrid sols in an alcoholic solution based on TEOS and an organic modified alcoxysilane were gelled by photopolymerization, and then dried at ambient pressure before sintering at 550°C. The result was a microporous gel with porosity higher than 90%. Chemical, physical, thermal, and mechanical characterizations were carried out on the microporous gel obtained by the nonsupercritical drying procedure. These results demonstrated the physical properties comparable with those of aerogels obtained by supercritical drying can be obtained. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of Pt–Pd/TS-1 Catalyst Preparation on Epoxidation of Olefins with Hydrogen Peroxide

The catalytic performance of the platinum–palladium/titanium silicalite, which was a common catalyst for the direct epoxidation of olefins with hydrogen and oxygen, was tested by epoxidation of allyl chloride with hydrogen peroxide. The epoxidation capacity of the TS-1catalyst was reduced after loading palladium and platinum on it. Ti leaching and crystallinity decrease were observed by XRD and FT-IR. The decomposition of hydrogen peroxide was accelerated by the supported Pd and Pt. These contributed to the loss of epoxidation capacity of TS-1. Ti leaching and crystallinity decrease were probably main causes. We propose that the Ti leaching had the most important influence on the loss of epoxidation capacity     

环己烯催化环氧化反应的研究新进展

综述了环己烯催化氧化法合成环氧环己烷的最新研究进展。近年来,催化环己烯环氧化越来越受到关注,因为它采用了来源方便和具有环保性质的氧化剂。介绍了环己烯催化环氧化的一些新进展。反应中采用了各种氧化剂如过氧化氢(双氧水),叔丁基过氧化氢(TBHP)和分子氧(O2),以及各种含有各种配体(如席夫碱、卟啉、酞菁和杂多酸)的过渡金属催化剂。对有关反应的机理进行了讨论。