Mesoporous materials cyclohexane

The first demonstration, to our knowledge, that the properties of a gas or liquid within a mesoporous cavity change was made by Dosseh et al. studying the properties of cyclohexane and benzene confined in MCM-41 and SBA-15. The effect was related to the influence of the inner surfaces of mesoporous silica. Other authors have further demonstrated the influence of confinement on the adsorption and properties of fluids within an ordered mesoporous material. Flowever, Fajula et were the... 

In this figure the oxygen permeation is plotted as a function of the relative pressure of cyclohexane. The curve, which was obtained from the membrane before the CVI-experiment, shows a clear transition point. This is indicative of a mesoporous material, in this case with a calculated Kelvin radius of 2.5 nm. For the membrane after CVI no such curve could be obtained and no clear transition point could be observed. This behaviour is representative for microporous materials. 

Catalyst (0.5 g), naphthalene (10 mmol), terf-BuOH (20 mmol), cyclohexane (100 ml), 2 h autoclave reactions at 160 °C. b A synthetic mesoporous material. 

The stability of SBA-1[140] toward washing with water was improved by increasing the crystallization time. Based on the results of n-heptane, cyclohexane, and nitrogen adsorption. SBA-1 is mechanically more stable as compared with hexagonal mesoporous materials such as MCM-41 and SB A-15, but exhibits similar mechanical stability as compared with the cubic MCM-48 material. 

Nano Au particles supported on mesoporous materials (SBA-15, MCM-41), which catalyze the oxidation of cyclohexane to Ol/One with oxygen, without solvent (conv. 18%, selectivity 93%) [25a]. Similar performance is obtained when Au is dispersed over other supports, for example, silica, alumina or titania [25b, c, d[. 

Typical N2 adsorption-desorption isotherms of the Ti02 samples calcined at 773 K are shown in Fig. 3. The isotherms of Ti02 samples prepared in EtOH are of a type IV characteristic of mesoporous materials according to the lUPAC classification with an H2 hysteresis-loop. However, larger mesoporous structures are obtained in cyclohexane. 

Relaxation time studies of the filling process of porous silica with water and cyclohexane have been used to establish whether the adsorption is homogeneous. It was found that water initially collected in small puddles at interstices in the structure, and then formed a surface layer over the silica surface before the remaining pore volume was filled. On the other hand, cyclohexane appeared to fill the smaller pores completely before spreading to the larger pores. A similar effect was observed for water adsorbing in a silica that had been chemically treated to make the surface hydrophobic. Thus, the fluid location in mesoporous materials at low loadings depends critically on the wettability of the surface. 

The hydroxylation of octane and cyclohexane catalyzed by Ti-MMM-1, a mixed- phase material (TS-1 and Ti-MCM-41) containing both micro- and mesopores, with aqueous H202 was reported by Poladi et al. (223). Ti-MMM-1 was found to be more active and selective in these hydroxylations than either Ti-MCM-41 or TS-1 the yield of alcohol was higher (Table XXVII). 

A similar development in this direction is the synthesis of a mixed-phase material containing both micro- and mesopores (Ti-MMM-1) (223). This material was synthesized by the addition of organic templates for mesopores (cetyltrimethylammonium bromide, CTABr) and micropores (tetrapropylammo-nium bromide, TPABr) at staggered times and the variation of the temperature of a single reaction mixture. Ti-MMM-1 is more selective (for oxidation of cyclohexane and of n-octane) than either Ti-MCM-41 or TS-1. The powder X-ray diffraction pattern indicates that the material contains both MCM-41 and MFI structures. The mixed phase contains framework Ti species and more atomic order within its walls than Ti-doped MCM-41. 

A material prepared by anchoring titanium(IV) on to the walls of a high-area, crystalline mesoporous silica (MCM41) has been used as an alkene epoxidation catalyst with alkyl hydroperoxides.204 The effect of replacing one of the three O—Si= groups to which the Ti(IV) is bound by an O—Ge= group is reported to lead to an increase in catalytic activity of up to 18% in die epoxidation of cyclohexene, although no explanation is provided and it is notable diat the selectivity towards the formation of cyclohexene oxide (versus cyclohexenol and cyclohexane-1,2-diol) was inferior to that with the non-modified system.205... 

The novel zeolite UTD-1 with titanium in the framework (up to 3.5% by weight) is an effective catalyst for the oxidation of cyclohexane, cyclohexene and 2,6-di-tert-butyl phenol. The catalytic behavior is similar to that of other large pore zeolites and mesoporous molecular sieves modified with titanium which includes solvents effects. Additionally, Ti-UTD-1 allows the use of oxidants and substrates too large for the commercial TS-1 catalyst. We are currently evaluating further the role of solvent and oxidant in an effort to improve selectivity as well as expand the utility of this material in oxidation catalysis. 

In this study, we reported the preparation of mesoporous Ti02 materials via the sol-gel method involving a co-assembly of titanium (IV) isopropoxide and mainly neutral soluble starch CTMACl is used only for comparative reason. Ethanol and cyclohexane were used as solvents. The effect of key parameters, including surfactant removal process either by washing and/or by calcination and the solvent nature are discussed. Ti02 samples were characterized by means of N2 adsorption-desorption experiments, X-ray Diffraction analysis, UV-vis spectrophotometer. Scanning Electron Microscopy and Atomic Force Microscopy. 

The above approach of using a diluent of an intermediate thermodynamic quahty during the polymerization of DVB has been intensively examined and, indeed, resulted in materials with enhanced proportions of mesopores. In order to create a rigid polymer of desired porosity, DVB (usually more than 30% in its mixture with styrenic co-monomers) must be copolymerized in the presence of a sufficient amount of a poor diluent (usually 100% or more of the volume of the co-monomers). Of crucial importance is the nature of the poor solvent. Besides cyclohexane, mixtures of a thermodynamically good solvent (ethylene dichloride, toluene, etc.) with precipitating media (hexane, octane, isooctane, higher aliphatic alcohols, etc.), taken in an appropriate proportion, can be applied. Microphase separation during the suspension copolymerization of such a mixture should take place when the major part of the co-monomers has converted into polymer. 

Very recently, Kluson et al. [268] prepared mesoporous titania by using a Triton X-lOO/cyclohexane/aqueous phase system with w = 1. The rationale behind the selection of such a low w value was that this amount of water should be mainly associated with the hydroxyl group of the surfactant and not compete with the oil phase for solvating the chain oxyethylene groups. Titanium isopropoxide was the source material for Ti. The titania crystallite size varied from 4.1 to 11.3 nm depending on the particle processing temperature. At 200 C, the product was amorphous to pseudoamorphous at 550"C, anatase started appearing, and rutile was found to appear in addition at 650"C. At 850°C, both anatase and rutile were obtained. 

Other rare earth elements ako found activity in these catalysts. The catalytic activity of cerium-incorporated cage-type mesoporous KlT-6 materials in oxidation of cyclohexene was explained as effect of from the framework with tetrahedral oxidic coordination [27]. When H2O2 is chemisorbed, only the distant oxygen is activated, by which cyclohexane could be oxidized by insertion of oxygen across the C—H bond, as illustrated in Scheme 21.1. Hence, cyclohexanol is the principal product in thk oxidation. Recyclability of the catalyst without leaching of cerium in the presence of the solvent was an important characteristic of this catalyst. Acetic acid as a solvent led to better results compared to either acetone or methanol. 

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