Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

硅烷化含钛介孔分子筛催化环己烯环氧化动力学

研究了气相沉积法制备的硅烷化含钛介孔分子筛(Ti/HMS)催化环己烯与异丙苯过氧化氢(CHP)的环氧化反应的宏观动力学.结果表明:环己烯与CHP的环氧化反应对催化剂的量表现为1级;对于环己烯和氧化剂CHP,随着浓度的增加,反应随之由1级向0级过渡,根据实验结果和反应机理,运用Rideal-Eley方法,提出了硅烷化Ti/HMS催化环己烯与CHP环氧化反应的动力学方程.     

Efficient catalytic epoxidation of olefins with hierarchical mesoporous TS-1 using TBHP as an oxidant

A series of hierarchical mesoporous TS-1 zeolites with MFI structure were successfully synthesized via hydrothermal route using amphiphilic organosilanes as pore directing templates. These materials were characterized by nitrogen sorption (for surface area, pore volume and pore size distribution), FTIR, SEM and UV–Visible spectroscopy. These materials are efficient catalysts for liquid phase epoxidation of olefins using TBHP as the oxidant. All these TS-1 samples oxidized cyclohexene selectively into epoxide. For the TS-1 sample with 4.4 % Ti complete conversion of cyclohexene into epoxide was observed.     

Niobium Containing Micro-, Meso- and Macroporous Silica Materials as Catalysts for the Epoxidation of Olefins with Hydrogen Peroxide

Niobia–silica mesoporous materials (xerogel, aerogel and MCM type) have been synthesized by sol–gel techniques using different co-solvents as templates. All materials are active catalysts in the epoxidation of cyclohexene with hydrogen peroxide, but only meso–macroporous aerogels give a stable and recyclable catalyst.     

Preparation of surface-silylated and benzene-bridged Ti-containing mesoporous silica for cyclohexene epoxidation

Organic–inorganic hybrid Ti-containing mesostructured materials were directly synthesized from tetrabutyl titanate in acidic media by using a non-ionic surfactant P123 as a structure-directing agent, tetraethoxysilane as an inorganic silicon source and 1,4-bis-(triethoxysilyl)benzene as organicsilica. The benzene-bridged Ti-containing periodic mesoporous organosilica Ti-SBA-15-ben was further modified by surface silylation with trimethylchlorosilane. The products were characterized by various means. We find the materials maintained good mesoporous structure, their hydrophobic properties were significantly improved after silanization, and the organic silicon source in the pore walls was favorable for obtaining tetravalent active titanium ions. The catalysts were evaluated in cyclohexene epoxidation with tertbutyl hydroperoxide as an oxidant agent. With Ti-SBA-15-ben as the catalyst, the epoxide selectivity and cyclohexene conversion were improved to 59.9 and 34.7 % respectively. Moreover, surface hydrophobization by silylation treatments further increased the epoxide selectivity to 71.5 %.     

Optimisation of olefin epoxidation catalysts with the application of high-throughput and genetic algorithms assisted by artificial neural networks (softcomputing techniques)

An olefin epoxidation Ti catalyst has been optimised by means of high-throughput experimentation involving materials synthesis, postsynthesis treatments, and catalytic testing. Softcomputing techniques for advanced experimental design have been used. The variables explored in the hydrothermal synthesis of Ti-silicate-based catalysts were: concentration of OH⁻, titanium, and surfactant. The probe reaction employed for the optimisation was the solvent-free epoxidation of cyclohexene, with tert-butylhydroperoxide as oxidant. The different catalyst groups detected by clustering analysis were studied by XRD and UV diffuse reflectance. Ti-mesoporous MCM-41 and MCM-48 molecular sieves were among the most active catalysts. The best performing catalysts were tested for epoxidation of different linear olefins.     

The Influence of Surface Modification on the Epoxidation Selectivity and Mechanism of TiSBA15 and TaSBA15 Catalysts with Aqueous Hydrogen Peroxide

The thermolytic molecular precursor method was used to introduce site-isolated Ti(IV) and Ta(V) centers onto the surface of a mesoporous SBA15 support. The resulting surface SiOH, TiOH, and TaOH sites were modified with a series of (N,N-dimethylamino)trialkylsilanes, Me₂NSiMe₂R (where R = Me, ⁿ Bu, or ⁿ Oc). Compared to the unmodified catalysts, the surface-modified catalysts are more active in the epoxidation of cyclohexene with H₂O₂ and exhibit a markedly greater selectivity for cyclohexene oxide (up to 58% for Ti(IV) and greater than 95% for Ta(V)). In situ spectroscopies were used to probe this phenomenon, and it was determined that a siloxy-capped Ti(IV) or Ta(V) site is essential to achieve the high epoxide selectivity.     

Recyclable Pd supported catalysts with low loading for efficient epoxidation of olefins at ambient conditions

Epoxides are a kind of useful synthetic intermediates. This work reports that activated carbon-supported Pd nanoparticles (Pd/C) efficiently catalyzed cyclohexene epoxidation in the presence of molecular oxygen and isobutyraldehyde with 91.5% conversion, 95.6% selectivity to cyclohexene oxide, ~ 400 h^− 1 activity and excellent stability for at least 5 catalytic runs. The epoxidation was examined on Pd catalysts supported on seven supports, and Pd/C exhibited superior catalytic performance possibly due to the inert support surface. The epoxidation reaction on Pd/C is via radical intermediate. Pd/C is also applicable to catalyze other olefins epoxidation.     

New Nb-containing SBA-3 mesoporous materials—Synthesis, characteristics, and catalytic activity in gas and liquid phase oxidation

The synthesis and characterization of NbSBA-3 mesostructured materials – the first hexagonally ordered mesoporous molecular sieves without extra framework Nb-oxide phase – are described in this paper. The effect of the synthesis medium (basic or acidic) and Nb source in the efficiency of niobium incorporation is discussed. A higher Nb content in the final material is reached when Nb(V) chloride is used instead of Nb(V) ammonium trisoxalate complex in the synthesis. All NbSBA-3 materials prepared in this work are very attractive catalysts in ODH of propane and epoxidation of cyclohexene and more effective than the corresponding NbMCM-41 and NbSBA-15 catalysts.     

Fabrication of VMn@mesoporous silica for epoxidation of cyclohexene

Vanadium-manganese containing mesoporous silica (VMnS) was prepared by an in situ grafting route by varying the wt% of vanadium and manganese. The materials were characterized by SXRD, BET-surface area, pore size distribution, SEM, EDAX-semiquantitative analysis, XPS, TPR, DRUV-vis, FTIR. The modification of silanol groups were evidenced from the characterization results. The activity of the catalysts was evaluated for cyclohexene epoxidation reaction. VMnS (2:2) showed highest conversion of 75% with selectivity 94%. Interestingly, only side product 2-cyclohexene-1-one (5%) was produced over the same catalyst.     

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%.     

Asymmetric Epoxidation of Styrene on the Heterogenized Chiral Salen Complexes Prepared from Organo-Functionalized Mesoporous Materials

Organosilane-modified mesoporous materials have been prepared under mild and acidic conditions by a solvent evaporation method using C₁₆TMABr surfactant as a template. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained under hydrothermal conditions had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on these organosilane-functionalized mesoporous silicas by a grafting method. The catalysts used in the asymmetric epoxidation of styrene and cis-stilbene and the effect of different mesoporous structures on the reactivity was investigated. Similar enantioselectivities were observed by using these heterogenized salen complexes as compared with reaction under homogeneous conditions.     

Epoxidation of cyclohexene over basic mixed oxides derived from hydrotalcite materials: Activating agent, solvent and catalyst reutilization

Synthesis and characterization of basic hydrotalcite-like derived catalysts were carried out and the resulting materials were tested in cyclohexene epoxidation. The reaction being dependent on the activating agent and the solvent of the reaction. Several nitriles and amides were used as activating agents and various compounds of different nature (protic and aprotic, polar and apolar) were analyzed as epoxidation solvents. The highest epoxide yield and cyclohexene conversion were achieved by using benzonitrile and methanol as activating agent and solvent, respectively. In the present work the reutilization of these solids in cyclohexene epoxidation has been tested by regeneration. The catalyst washed with the solvent after one reaction did not enhance the catalytic properties of the fresh solid. Nevertheless the activation of the solid up 600 °C provided a good activity after four runs.     

Hydrothermal synthesis of mesoporous titanosilicate with the aid of amphiphilic organosilane

Mesoporous MFI-type titanosilicates (TS-1) were hydrothermally synthesized with the aid of amphiphilic organosilane and the effects of the amphiphilic organosilane on the structural and textural properties of the resultant materials were investigated. The physicochemical properties of the samples were characterized by various techniques and their catalytic performance was investigated by the epoxidation of cyclohexene with hydrogen peroxide. The content of organosilane added was essential for the formation of uniform mesopore in TS-1, and greatly influenced the crystallinity. Highly crystallined TS-1 with uniform mesopores of 3.7 nm diameter was successfully synthesized. The mesoporous TS-1 preserved tetrahedrally coordinated Ti ions in the framework, but it was featured with more hydrophobic surface and less defect sites in comparison to conventional TS-1. Mesoporous TS-1 showed a higher conversion for the epoxidation of cyclohexene owing to an easier access of bulky molecules to the catalytic active sites. Mesoporous TS-1’s higher hydrophobicity made its epoxide selectivity two times as much as that of conventional TS-1.     

CUII(Sal-Ala)/MgAlLDH and CUII(Sal-Phen)/MgAlLDH as novel catalytic systems for cyclohexene oxidation by H2O2

We present here Cu^II(Sal-Ala)/MgAlLDH and Cu^II(Sal-Phen)/MgAlLDH complexes as novel catalytic systems for the cyclohexene oxidation by H₂O₂. The physical–chemical properties of the catalysts were investigated by XRD, FTIR, UV-Vis, XPS and TGA techniques. We present evidence that the properties of the Cu^II-based complexes and the specific properties of the LDHs matrix both beneficially contribute to establish the cyclohexene catalytic oxidation efficiency. Cu^II(Sal-Ala)/MgAlLDH showed the best catalytic activity with a cyclohexene conversion of 81% and 78% epoxide selectivity. The leaching effect of copper has not observed, and the CH epoxidation yields can be maintained during five catalytic cycles.     

Effect of pore size on the performance of mesoporous material supported chiral Mn(III) salen complex for the epoxidation of unfunctionalized olefins

A series of mesoporous MCM-41 and MCM-48 materials with different pore sizes were synthesized and used as supports to immobilize chiral Mn(III) salen complex. The heterogeneous catalysts were characterized by XRD, FT-IR, DR UV–vis, and N₂ sorption, and the results indicated the successful immobilization of chiral Mn(III) salen complex. The confinement effect of pore size on the catalytic performance of the heterogeneous catalysts was studied for the asymmetric epoxidation of unfunctionalized olefins with m-chloroperoxybenzoic acid as an oxidant. It was found that the conversions and enantiomeric excess (ee) values were closely correlated with the pore sizes of parent supports. The catalysts immobilized on the large-pore mesoporous supports exhibited higher conversions, and for the catalysts immobilized on MCM-41 materials, the ee values improved with increasing pore size. However, for the MCM-48 material-supported catalysts, the compatible pore size of the support with the substrate was beneficial for obtaining higher enantioselectivity in olefin epoxidation.     

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。     

Enhanced expoxidation activity of Ti-mesoporous catalysts containing organic–inorganic porewall

Surfactant templated Ti-containing organic–organic mesoporous catalysts which were synthesized from one step co-condensation of the precursors, showed enhanced liquid phase cyclohexene epoxidation activity and greater deactivation resistance than the parent Ti-MCM-41, with tert-butyl hydroperoxide as oxidant. The order of reactivity observed was Ti-MCM-41-phenylene > Ti-MCM-41-biphenylene > Ti-MCM-41-ethylene > Ti-MCM-41. In the presence of water, the Ti-MCM-41-phenylene catalyst showed up to 3.5-fold enhancement in activity over Ti-MCM-41. The enhancement in catalytic activity was attributed to improvement in surface hydrophobic characteristic from the incorporation of organic functionalities.     

Catalytic Characterization of Mesoporous Ti–Silica Hollow Spheres

Titanium–silica hollow spheres (TSHS) with a mesoporous shell were synthesized using an inverse multiple oil–water–oil (O/W/O) emulsion. These novel materials show interesting potential for catalysis. Excellent catalytic performance was found in the epoxidation of cyclohexene with tert-butylhydroperoxide. The investigation of the titanium environment by UV–vis, Raman and FTIR spectroscopy showed that at low Ti loading only isolated species are present and catalytic measurements demonstrated that these species are the active sites for this reaction. At higher loading Ti–O–Ti microdomains are present and they do not exhibit any significant catalytic activity.     

Epoxidation of Cyclohexene with Air over the Composite Catalysts of Mn-mont Coordinated with Ligands

The catalytic activity of the composite catalysts of Mn-mont (where mont represents montmorillonite) coordinated with ligands for the epoxidation of cyclohexene by air under Mukaiyama conditions was studied. The composite catalysts were characterized by atomic absorption spectroscopic analysis, elemental analysis, fourier transform infrared spectra, diffuse reflectance ultraviolet visible spectra, X-ray photoelectron spectroscopy, powder-X-ray-diffraction, and scanning electron microscopy measurements. The effects of various reaction conditions on the catalytic reaction were studied. Experimental results indicated that the catalysts performed excellent activity for the epoxidation of cyclohexene by air. Repeated runs indicate that the catalyst is stable for 3 cycles. The composite catalysts of Mn-mont coordinated with ligands are economical and environmentally friendly for the epoxidation of cyclohexene.