Immobilization of new Mn(salen) complex over MCM-41 and its activity in asymmetric epoxidation of styrene

New tetradentate chelates of bis-Schiff bases were synthesized and then these chiral salen ligands were immobilized over mesoporous MCM-41 by using the ion-exchange method. The efficiency of the chiral catalyst was examined in the asymmetric epoxidation of styrene. Chiral Mn(salen) complexes immobilized onto mesoporous MCM-41 were stable during the reaction without any leaching and exhibited relatively high enantioselectivity for epoxidation as compared with homogeneous complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Asymmetric catalysis by chiral salen complexes immobilized on mesoporous materials having modified pore channel system by dimethylcarbonate

The mesoporous materials having bimodal pore structure were synthesized by treatment of dimethylcarbonate (DMC) in the presence of metal salts as a catalyst. The pore system was characterized by BET, TEM analysis and by comparing the catalytic activity under the same conditions. The chiral (salen) Co-MX₃ immobilized on SBA-15 and MCM-48 which were partially desilylated by DMC showed higher activity for the enantioselective kinetic resolution of terminal epoxides with H₂O and phenols, relative to original SBA-15 and MCM-48 having regular pore channels. The heterogeneous catalysts can offer practical advantages of the facile separation from reactants and products, as well as recovery and reuse.     

Synthesis of a siliceous MCM-41 using C22TMACL template and preparation of heterogenized new chiral salen complexes

Purely siliceous MCM-41 has been prepared under both mild and acidic conditions by a solvent evaporation method using C₁₆TMABr and C₂₂TMACl surfactant as templates. A hydrothermal synthesis was also carried out by utilizing a method of adjusting the gel pH to 10. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained in the hydrothermal synthesis had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on the siliceous MCM-41 by a new grafting method using 3-aminopropyltrimethylsilane and diformylphenols. These ligands on MCM-41 were stable during the reactions. High enantioselectivities were displayed in the epoxidation of styrene by using these heterogenized salen complexes.     

Synthesis and catalytic activity of new macrocyclic chiral salen complexes

New macrocyclic chiral salen complexes were synthesized and then the efficiency of these fully symmetrical ligands as catalysts was evaluated in the asymmetric epoxidation of olefins and borohydride reduction of ketones. The symmetrical macrocyclic salen complexes exhibited a relatively high enantioselectivity in these reactions.     

Asymmetric epoxidation of unfunctionalized olefins catalyzed by Mn(III) salen complex immobilized on MCM-48

Chiral Mn(III) salen complexes were supported on mesoporous molecular sieve MCM-48 and employed as catalyst in the asymmetric epoxidation of some unfunctionalized olefins. The as-synthesized catalysts showed excellent enantioselectivity than homogeneous catalysts for α-methylstyrene and the highest ee value (up to >99%) was obtained. Furthermore, these catalysts were also effective for bulkier olefins such as indene and 1-phenylcyclohexene. Compared to homogeneous counterparts, the heterogeneous catalysts are more stable and can be recycled three times without loss of enantioselectivity.     

A new and easy method for anchoring manganese salen on MCM-41

This work reports a new method to covalently attach manganese salophen complex onto MCM-41, using a diisocyanate as a binder. The prepared catalyst was tested on the liquid phase limonene oxidation reaction. Diluted t-Butyl hydroperoxide was used as oxygen supplier. Limonene oxide, carveol and carvone are formed, but the main product obtained was a polymer. The preservation of the MCM-41 channel system was checked by X-ray diffraction and nitrogen adsorption analysis. The use of the same catalyst sample in four consecutive experiments, without loss of activity, is a confirmation of the success of the anchoring process.     

Application of new unsymmetrical chiral Mn(III), Co(II,III) and Ti(IV) salen complexes in enantioselective catalytic reactions

New unsymmetrical chiral salen complexes were synthesized and the efficiency of Mn(III), Ti(IV), Co(II) and Co(III) type catalysts were examined in the enantioselective epoxidation of styrene and α‐methylstyrene, the trimethylsilylcyanation of benzaldehyde, the borohydride reduction of aromatic ketones and asymmetric hydrolysis of epoxides to diols, respectively. A very high level of enantioselectivity was attainable over the unsymmetrical chiral salen complexes prepared mainly from salicylaldehyde and 2‐formyl‐4,6‐di‐tert‐butylphenol derivatives. Enantiomeric excess of the corresponding reaction product obtained using unsymmetrical chiral salen catalysts was generally higher than that over conventional symmetric chiral salen catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.     

微波固相法制备MCM-41固定 氯化铝催化剂及其催化性能

采用微波固相法制备了MCM-41固定氯化铝固体酸催化剂。以合成乙酸正戊酯为探针反应,考察了氯化铝不同负载量、反应时间、微波功率对其催化性能的影响。结果表明,氯化铝负载量为6 mmol/g、反应时间为 15 min、微波功率为750 W时,所制得的催化剂活性最好,其酯化率可达92.7%。     

负载金属Salen配合物催化剂在催化反应中的应用研究进展

对负载金属salen配合物从负载方法、适用反应等方面的研究成果进行了总结,对不同负载方法的优缺点进行了阐述,并对这类催化剂工业化应用前景和拟解决问题进行了探讨。     

Synthesis of polymeric salen complexes and application in the enantioselective hydrolytic kinetic resolution of epoxides as catalysts

The polymeric (salen) Co(III) catalysts containing various counter anions have been synthesized, and the asymmetric catalytic activities of these newly synthesized polymer-type salen complexes were investigated in the HKR of terminal epoxides. The polymeric chiral salen Co(III) complexes catalyze the hydrolysis of epichlorohydrine, 1,2-epoxybutane, 1,2-epoxyhexane and epoxystyrene with very high enantioselectivities under mild conditions. The catalysts could be recovered and reused several times without further treatment after reaction, showing no loss of activity and enantioselectivity.     

Pt/MCM-41 catalyst for selective catalytic reduction of nitric oxide with hydrocarbons in the presence of excess oxygen

First results are reported on the use of MCM-41 mesoporous molecular sieve as the support for Pt for the selective catalytic reduction of NO by hydrocarbons in the presence of O₂. MCM-41 provided the highest specific NO reduction rates for Pt as compared with all other supports reported in the literature, i.e., Al₂O₃, SiO₂ and ZSM-5. This revised version was published online in July 2006 with corrections to the Cover Date.     

Absorption of carbon dioxide into glycidyl methacrylate solution containing the triethylamine immobilized ionic liquid on MCM-41 catalyst

An ionic liquid (TEA-MS41), triethylamine-immobilized on chloropropyl-functionalized MCM-41, was synthesized by a grafting technique through a co-condensation method and used as a catalyst in the reaction of carbon dioxide with glycidyl methacrylate (GMA). CO₂ was absorbed into the heterogeneous system of the GMA solution and dispersed with solid particles of the catalyst in a batch stirred tank with a plane gas-liquid interface at 101.3 kPa. The absorption of CO₂ was analyzed by using mass transfer accompanied by chemical reactions based on film theory. The proposed model fits the measured data of the enhancement factor to obtain the reaction rate constants. Solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide influenced the reaction rate constants.     

Catalytic combustion of toluene on Cu-Mn/MCM-41 catalysts: Influence of calcination temperature and operating conditions on the catalytic activity

Catalytic combustion of toluene on Cu-Mn/MCM-41 catalyst was performed in tubular flow reactor operated at atmospheric pressure. The effect of catalyst pre-treatment temperatures on the catalytic activity and stability was investigated. Some reaction variables, such as inlet concentration of toluene and oxygen, reaction temperatures and space velocities were varied over wide ranges, and the influence of different reaction conditions on toluene conversion was discussed. It is showed that the catalytic activity was significantly affected by calcination temperatures between 300 and 800 °C, and oxygen concentration, toluene concentration and space velocity are all key experimental factors to optimize the toluene combustion activities. The objective of this study was to investigate catalytic properties of Cu-Mn/MCM-41 catalysts prepared at different calcination temperatures, in order to obtain additional information to prepare an efficient and highly active catalyst at low temperature.     

The entrapment of UO2 in mesoporous MCM-41 and MCM-48 molecular sieves

A method based on direct template-ion-exchange was employed for the entrapment of UO₂²⁺ ions in MCM-41 and MCM-48 molecular sieves via swapping of cetyltrimethylammonium cations present in the mesoporous channels by the UO₂²⁺ ions in an aqueous solution. The samples were characterized by XRD, FT-IR, and ICP-AES techniques. The entrapment of UO₂²⁺ ions is facilitated by the large pore size vis-a-vis the high surfactant content in the as-synthesized host materials. A higher loading of UO₂²⁺ ions was achieved in MCM-48 as compared to MCM-41, which could be attributed to its three-dimensional pore system and higher surfactant-to-silica ratio. FT-IR results provide an evidence of a strong binding of UO₂²⁺ groups with the defect silica sites of mesoporous molecular sieves.     

不同碱介质对合成硅基MCM-41的影响

研究了在较高的硅／表面活性剂物质的量比(10)体系中，采用不同的碱介质(氨水、乙二胺、三乙醇胺／NaOH)来合成MCM-41。通过XRD，N2吸附一脱附等表征手段，分析了不同碱介质体系对制备MCM-4l的影响。结果显示。弱碱介质(NH3，EDA)有利于提高MCM-41的热稳定性；而采用混合碱质(三乙醇胺／NaOH)，则可在一定程度上改善MCM-41的水热稳定性，但随着三乙醇胺量的增加，材料的孔径会相应的减小。     

Enhanced CuCl dispersion by regulating acidity of MCM-41 for catalytic oxycarbonylation of ethanol to diethyl carbonate

CuCl supported on molecular sieves has attracted increasing attention in catalyzing oxidative carbonylation of ethanol to diethyl carbonate. Mesoporous MCM-41 has been widely used as catalyst support due to its large surface area and well defined mesoporous structure. Considering its intrinsic weak acidity, MCM-41 was modified by a simple impregnation method to incorporate Al. The incorporation of Al components resulted in the high dispersion of Cu species and the increase of acid sites without changing the mesoporous structure of MCM-41, and thus enhanceed the catalytic activity of CuCl/MCM-41for diethyl carbonate synthesis.     

制备条件对介孔分子筛MCM-41形貌的影响研究

本文以正硅酸乙酯(TEOS)为硅源,十六烷基三甲基溴化铵(CTAB)为介孔模板剂制备MCM-41介孔分子筛,通过改变制备体系条件来调控MCM-41的形貌,考察了制备体系水用量、制备体系氨水用量、TEOS滴加速率对所得MCM-41产物形貌的影响。结果表明:制备体系水用量和氨水用量增大会使所得产物由棒状向球形颗粒转变,TEOS滴加速率加快有利于形成尺寸均匀的棒状MCM-41。最后对MCM-41形貌演变过程进行了分析。     

苯乙烯在MCM-41介孔材料中聚合的研究

The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).     

介孔分子筛MCM-41在有机催化中的研究进展

介绍了近几年MCM-41在环氧化、加氢反应、烷基化、酯化等有机反应中的应用。介孔分子筛MCM-41具有较高的比表面和规整的结构,以及表面带有羟基,是催化剂的优良载体。因此,可以将催化剂引入到MCM-41的结构中,从而提高其性能。认为应在介孔分子筛的水热稳定性、研究合成机理、合成方法等方面加强研究,对介孔分子筛在有机化工催化领域中的应用现状及前景进行了分析。