Epoxidation of olefines with PDMS membranes containing zeolite occluded manganese diimine complexes

A new composite catalyst for selective epoxidation of olefins with tert-butyl hydroperoxide (tBHP) is reported. The catalyst contains manganese diimine complexes (cis-Mn bis-2,2′-Bipyridyl), occluded within a NaY zeolite, in turn incorporated in a polydimethylsiloxane membrane (cis-[Mn(bpy)₂]²⁺-NaY-PDMS). The three-step synthesis consists of a Mn²⁺exchange of NaY, ligand sorption to form cis-[Mn(bpy)₂]²⁺-NaY and incorporation of the latter in a PDMS membrane. The major differences between [Mn(bpy)₂]²⁺-NaY as such and occluded in PDMS are observed in the sorption and catalytic characteristics. With the membrane system, the use of a solvent becomes obsolete. Whereas optimal cyclohexene oxidation with [Mn(bpy)₂]²⁺-NaY occurs with hydrogen peroxide in acetone, tBuOOH proves to be a better oxidant for [Mn(bpy)₂]²⁺-NaY-PDMS. The reactions in batch and fed-batch reactors are discussed. A simple regeneration procedure, monitored by FT-IR spectroscopy is proposed.     

Dehydrogenation of Cyclohexene on Platinum Nanoclusters on a Thin Film of Al2O3/NiAl(100)

Using a scanning-tunneling microscope, reflection high-energy electron diffraction and photoelectron spectra with synchrotron radiation, we investigated the temperature dependence of the dehydrogenation of cyclohexene (C₆H₁₀) adsorbed on Pt nanoclusters supported on an ultra-thin film of Al₂O₃/NiAl(100). The Pt clusters, grown by vapor deposition, are structurally ordered and exhibit a mean diameter 2.2 nm and height 0.4 nm. The progress of dehydrogenation was monitored through the temporal variation of C 1s photoelectron spectra; analysis of these features revealed that the dehydrogenation of cyclohexene with increasing sample temperature occurs as a sequential process beginning around 150 K, a temperature significantly less than that for Pt single-crystal surfaces. The dehydrogenation behavior, particularly the decomposition into elemental carbon, is found to vary with Pt coverage.     

Methyltrioxorhenium-catalyzed epoxidation of alkenes with hydrogen peroxide as an oxidant and 1-methyl-3-(butyl-4-sulfonate) imidazolium betaine as an additive

In the methyltrioxorhenium-catalyzed epoxidation of alkenes, 1-methyl-3-(butyl-4-sulfonate) imidazolium betaine (MBSIB) was used as an additive, and 30% H₂O₂ was used as an oxidant. The introduction of 10-fold excess MBSIB improved the selectivity of epoxide formation without reducing the reaction rate by increasing the polarity of the catalytic system. Furthermore, the MTO–MBSIB system was stable throughout the entire catalytic run and increased the TON of the epoxidation of alkenes.     

Preparation and catalytic properties of platinum dioxide nanoparticles: A comparison between conventional heating and microwave-assisted method

Using platinum chloride, sodium hydroxide, sodium acetate, and polyvinylpyrrolidone as starting materials, platinum dioxide nanoparticles with small particle diameter and narrow distribution were prepared by microwave irradiation and conventional heating, respectively. UV–vis spectrophotometer was used to trace the hydrolytic decomposition of platinum chloride and the formation of platinum dioxide nanoparticles. X-ray powder diffraction and transmission electron microscopy were employed to characterize the crystalline structure and the morphologies of the obtained nanoparticles. Gas chromatography was performed to investigate their catalytic properties for hydrogenation of cyclohexene. The results revealed that (i) the obtained nanoparticles have the same crystalline structure; (ii) the nanoparticles obtained by microwave irradiation were smaller and more narrowly distributed than those obtained by conventional heating; (iii) the activation time of the catalyst markedly influences the catalytic activity; (iv) the particles obtained by microwave irradiation showed higher catalytic activity than those obtained by conventional heating for hydrogenation of cyclohexene.     

1,6-己二醛合成工艺研究

根据环己烯分子结构特点及相关反应的基础理论,提出在甲酸作为载氧剂的条件下,以过氧化氢氧化环己烯制备反式-1,2-环己二醇的工艺路线;并使用高碘酸钠/硅胶体系氧化反式-1,2-环己二醇制备1,6-己二醛.通过单因素实验法对在合成过程中的物料配比、反应温度、反应时间、重结晶方法等诸多因素对反应的影响进行考察.以气相色谱对产品纯度进行分析,得出反式-1,2-环己二醇及1,6-己二醛的纯度分别为98.93%和99.97%,并利用GC、红外光谱、核磁共振等分析方法对其产品化学结构进行确认.     

Structural and catalytic properties of Ti–MCM-41 synthesised at room temperature up to high Ti content

A study of the pore structural properties and catalytic activity of MCM-41 containing titanium, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium alcoxides, cationic surfactants and ammonia is presented. The influence of different metal sources (titanium ethoxide, isopropoxide or n-butoxide), alcohols (ethanol or propan-2-ol), metal content (2  Si/Ti  100) and surfactants (tetra-, hexa- or octadecyltrimethylammonium bromide) is considered. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77 K and diffuse reflectance UV–Vis spectroscopy. The catalytic activity was evaluated in the model reaction of oxidation of cyclohexene with anhydrous tert-butylhydroperoxide, for representative samples. It is concluded that this method allows the preparation in a short period of time of well structured and catalytically active Ti–MCM-41. Down to Si/Ti = 10 the materials have high pore volumes and very uniform pore size, with highest conversion and excellent selectivity demonstrated in the compositional range 30  Si/Ti  100, corresponding to materials containing predominantly isolated and tetracoordinated Ti. The increase in Ti content to Si/Ti ratios of 10 and 5 implied a reduction both in conversion and selectivity, although the MCM-41 structure was still observed for Si/Ti = 2.     

Effect of superfine particles of alumina incorporated in the cavities of mordenite in enhancing selectivity

Alumina has been incorporated in the cavities of mordenite by the hydrolysis of Al³⁺ ions in the cavities with moist ammonia gas, following calcination at 450°C. The incorporation of the superfine particles of alumina into the cavities of the mordenite is assessed on the basis of the data of MAS ²⁷Al NMR measurements, X-ray powder diffraction and the amount of saturated adsorption of nitrogen for FAL/MZ. The acid properties, assessed using NH₃ TPD and FTIR studies, show the presence of Brønsted and Lewis acid sites on the catalyst, and an increase in acidic sites on incorporating alumina. The dehydrogenation selectivities of FAL/MZ, Al³⁺/MZ, H⁺/MZ, and Na⁺/MZ have been investigated. Brønsted acid sites largely enhance the ring-cleavage, whereas this incorporation of superfine particles of alumina significantly suppresses the ring-cleavage. Therefore, the incorporation of the superfine particles increases remarkably in the cyclohexene selectivity.     

新方法合成氯代环己烷

由氯化氢与环己烷和环己烯混合物的加成反应,既合成了氯代环己烷,又使混合物便于分离。     

Selective hydrogenation of benzene to cyclohexene using a suspended Ru catalyst in a mechanically agitated tetraphase reactor

The reactivity on unsupported Ru based catalyst in benzene selective hydrogenation to cyclohexene has been studied. The reaction has been carried out in a tetraphase slurry reactor at 423 K, at 5 MPa, in the presence of two liquid phases: benzene and an aqueous solution of ZnSO₄ 0.6 mol l⁻¹. A detailed study of the influence of the transport phenomena on the reactivity of the catalyst has been carried out. No correlation has been found between the characteristic numbers of Weeler–Weisz and of Carberry mass transport at external liquid/solid interface or into the catalyst pores for both benzene and hydrogen and the selectivity of the catalyst. The main features of the catalysts are the strong dependence between the catalysts preparation procedure and their activity and selectivity. In particular the influence of the alkaline or the earth alkaline hydroxide, employed in the precipitation of the Ru precursor, on the selectivity, has been studied. Hydrogen chemisorption measurements indicate that the amount of weakly adsorbed hydrogen depends on the nature of the base employed in the precipitation step.     

Upgrading of cyclohexanone to hydrocarbons by hydrodeoxygenation over nickel–molybdenum catalysts

Cyclohexanone is largely generated in the direct or indirect conversion of lignin-derived bio-oils. Hence, the upgrading of cyclohexanone, i.e. deoxygenation in the presence of hydrogen is of great interest. In this regard, two nickel-molybdenum catalysts on alumina support were investigated in the temperatures up to 400 °C and pressures up to 15 bar. High activity, selectivity, and yield were achieved by utilizing these catalysts at the studied condition. The main products of the upgrading of cyclohexanone were C₆, C₇, and C₁₂ cyclic, aromatic, and bicyclic including cyclohexane, cyclohexene, benzene, and cyclohexylbenzene. The results of the present study imply that these catalysts are beneficial in producing hydrocarbon-rich products from cyclohexanone and lignin-derived bio-oils. Based on the achievements of the present study, the nickel-molybdenum catalyst composed of 1.14 wt% nickel and 14.27 wt% molybdenum showed about 87%, 100%, and 116% conversion of cyclohexanone, total hydrocarbon selectivity, and total hydrocarbon yield, respectively. The optimum condition for obtaining such results was at 400 °C and 8 bar.