Hexagonal mesoporous silicas

Recently very reacdve solid bases have been devised, which are prepared by derivadzadon of amorphous silica and hexagonal mesoporous silica fHMSi v/ith the dimethylaminopropyl group fEq 4 113 ... 

Klotz, M., Ayral, A., Guizard, C. and Cot, L. (2000) Synthesis conditions for hexagonal mesoporous silica layers. Journal of Materials Chemistry, 10 (3), 663-669. 

The titanosilicate version of UTD-1 has been shown to be an effective catalyst for the oxidation of alkanes, alkenes, and alcohols (77-79) by using peroxides as the oxidant. The large pores of Ti-UTD-1 readily accommodate large molecules such as 2,6-di-ferf-butylphenol (2,6-DTBP). The bulky 2,6-DTBP substrate can be converted to the corresponding quinone with activity and selectivity comparable to the mesoporous catalysts Ti-MCM-41 and Ti-HMS (80), where HMS = hexagonal mesoporous silica. Both Ti-UTD-1 and UTD-1 have also been prepared as oriented thin films via a laser ablation technique (81-85). Continuous UTD-1 membranes with the channels oriented normal to the substrate surface have been employed in a catalytic oxidation-separation process (82). At room temperature, a cyclohexene-ferf-butylhydroperoxide was passed through the membrane and epoxidation products were trapped on the down stream side. The UTD-1 membranes supported on metal frits have also been evaluated for the separation of linear paraffins and aromatics (83). In a model separation of n-hexane and toluene, enhanced permeation of the linear alkane was observed. Oriented UTD-1 films have also been evenly coated on small 3D objects such as glass and metal beads (84, 85). 

The variety of finely divided silica known as hexagonal mesoporous silica (HMS) [6,34] is generally prepared by the copolymerization of a silica precursor such as tetraethylorthosilicate (TEOS), in presence of a suitable template. This acid or base catalyzed reaction follows the sol-gel route and it has been found [28] that during silica preparation by this technique, it is also possible to add an organotriethoxysilane [RSi(OEt)3] that would... 

HMS-C-SbF3 = Sbp3 supported on hexagonal mesoporous silica... 

HMS-C-SbFi = SbF2 supported on hexagonal mesoporous silica. h MTO supported on poly(4-vinylpyndine) 25% cross-linked with divinylbenzene. 

Supercritical Fluid Extraction of Amine Surfactant in Hexagonal Mesoporous Silica (HMS)... 

Supercritical carbon dioxide modified with 10 vol% methanol has been employed for the removal of the amine surfactant in hexagonal mesoporous silica (HMS). The effects of temperature and pressure on the extraction efficiency have been extensively studied. It has been found that within an hour, as high as 96% of the amine surfactant can be extracted at a relatively mild condition of 85°C and 100 bar. At constant pressure, high extraction efficiencies are obtained at 50 and 85°C while at constant temperature, high efficiencies occur at 100 bar and 250 bar. This work establishes the feasibility of using supercritical fluid extraction (SFE) for the removal of the amine surfactant. In fact, it has been discovered that SFE produces EIMS of more enhanced mesoporosity as compared to that of calcination. 

In 1995, Tanev and Pinnavaia [1] have reported the synthesis of a new type of mesoporous molecular sieve designated as the hexagonal mesoporous silica (HMS). Instead of using the ionic inorganic precursor and surfactant as in the case of MCM-41 [2], HMS is manufactured by hydrolysis reaction between a neutral inorganic precursor, tetraethyl-orthosilicate (TEOS) and a neutral primary amine surfactant (8-18 carbons). HMS possesses numerous favourable characteristics, but, like MCM-41, its synthesis process can only be concluded by the removal of the surfactant. This was reportedly done either by calcination at 630°C or by warm ethanol extraction [1]. 

Same preparation as CHRISS but uses 24 A pore size hexagonal mesoporous silica (HMS) as the support. 

Immobilised complex ligand structures incorporated into hexagonal mesoporous silica gels can be used to bind other metals. We are currently working on other systems and we will describe these elsewhere. 

Figure 10 Preparation of solid sulphonic acid based on a hexagonal mesoporous silica. Key features of the materials are ...

New Organically Modified Hexagonal Mesoporous Silicas Preparation and Applications in Catalysis... 

Structural Analysis of Hexagonal Mesoporous Silica Films Produced from Triblock-Copolymer-Structuring Sol-Gel... 

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