Ordered mesoporous materials in catalysis

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Chemical strategies to design textured materials: from microporous and mesoporous oxides to nanonetworks and hierarchical structures.

SBA-15 ordered mesoporous silicas were synthesized using the method reported by Zhao et al. The structures of these materials were characterized using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nitrogen adsorption. The samples were found to exhibit structural properties similar to those reported earlier. Our study confirmed that the size of primary mesopores of SBA-15 can be tailored by the choice of synthesis temperature and that SBA-15 exhibits a significant amount of disordered micropores and small mesopores. The volume and size of these complementary pores were found to be dependent to some extent on the synthesis/aging temperature. It was shown that the washing of as-synthesized SBA-15 in water or ethanol was accompanied by an appreciable structural shrinkage and led to the removal of a significant part of the polymeric template. Therefore, washing needs to be avoided if one wants to isolate SBA-15 without appreciable loss of the template. It was confirmed that water-washed...

Characterization of the Porous Structure of SBA-15

because itdetermines the mechanism and rate of cell uptake of ananoparticle and its ability to permeate through tissue. Theinvestigation of particle size effects will impact on allapplications of nanoparticles in biomedicine. It has beenfoundthatparticlesizecanaffecttheefﬁciencyandpathwayofcellularuptakebyinﬂuencingtheadhesionoftheparticlesandtheir interaction with cells.

Size effect on cell uptake in well-suspended, uniform mesoporous silica nanoparticles.

Verified syntheses of mesoporous materials

Three different water-alcohol cosolvent systems were used to assemble mesoporous molecular sieve silicas with wormhole framework structures (previously denoted HMS silicas) from an electrically neutral amine surfactant (S{degree}) and a silicon alkoxide precursor (I{degree}). The fundamental particle size and associated textural (interparticle) porosity of the disordered structures were correlated with the solubility of the surfactant in the water-alcohol cosolvents used for the S{degree}I{degree} assembly process. Polar cosolvents containing relatively low volume fractions of C{sub n}H{sub 2n+1}OH alcohols (n = 1--3) gave heterogeneous surfactant emulsions that assembled intergrown aggregates of small primary particles with high textural pore volumes (designated HMS-HTx). Conversely, three-dimensional, monolithic particles with little or no textural porosity (designated HMS-LTx) were formed from homogeneous surfactant solutions in lower polarity cosolvents. Aluminum substituted AL-HMS-HTx analogues with high textural porosity and improved framework accessibility also were shown to be much more efficient catalysts than AL-HMS-LTx or monolithic forms of hexagonal AL-MCM-41 for the sterically demanding condensed phase alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol. Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies verified the textural differences between wormhole HMS and electrostatically assembled hexagonal MCM-41 and SBA-3 molecular sieves. Power law fits to the scattering data indicated a surface fractal (D{submore » s} = 2.76) for HMS-HTx, consistent with rough surfaces. A second power law at lower-q indicated the formation of a mass fractal (D{sub m} = 1.83) consistent with branching of small fundamental particles. Hexagonal MCM-41 and SBA-3 silicas, on the other hand, exhibited scattering properties consistent with moderately rough surfaces (D{sub s} = 2.35 and 2.22, respectively) and large particle diameters ({much{underscore}gt}1 {micro} m). HMS-LTx silicas showed little or no mass fractal character (D{sub m} = 2.87), and no surface fractal scattering.« less

Thomas R. Pauly

Papers

Textural Mesoporosity and the Catalytic Activity of Mesoporous Molecular Sieves with Wormhole Framework Structures

A new nonionic surfactant pathway to mesoporous molecular sieve silicas with long range framework order

Mesoporous molecular sieve catalysis: Relationships between reactivity and long range structural order/disorder