Chih-Yuan Tang

Synthesis and catalytic activity of amino-functionalized SBA-15 materials with controllable channel lengths and amino loadings

Aminopropyl-functionalized SBA-15 mesoporous materials (NH2-SBA-15) with different lengths of channeling pores and aminopropyl loadings up to 2.6 mmol g−1 were synthesized by one-pot co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyltrimethoxysilane (APTMS) with the aid of appropriate amounts of Zr(IV) ions and NaCl. The morphologies and pore lengths of the resultant materials were tuned by varying the Zr/TEOS and NaCl/TEOS molar ratios in the synthesis gels. The assembly processes were examined by in situsmall-angle X-ray scattering (SAXS) and conventional characterization techniques. Accordingly, TEOS prehydrolysis for around 2 h in the synthesis solution before the addition of APTMS was essential for preparing platelet NH2-SBA-15 materials with well-ordered p6mmpore structure and narrowly distributed pore size distribution, due to the strong interference from APTMS. When applying these materials as solid base catalysts in solvent-free flavanone synthesis, the platelet material with short-channeling poresca. 200–300 nm was superior to the rod-like and fiber-like counterparts with lengthy channels in the micrometre scale due to better molecular diffusion and less possibility of pore blockage. Furthermore, the platelet materials with high surface areas (∼450 m2 g−1) and amino loadings around 1.4–1.8 mmol N g−1 were the most efficient catalysts for flavanone synthesis, and the high activity was retained by a simple regeneration method.

Effect of calcination on the structure and catalytic activities of titanium incorporated SBA-15

Well-ordered Ti-incorporated SBA-15 materials (shortly termed Ti–SBA-15) with Ti loading up to 10 mol% of Si were prepared by a one pot co-condensation method using tetraethyl orthosilicate (TEOS) as the silica source and titanium oxychloride as the Ti source in an acidic environment close to the isoelectric point of silanol groups (pH = 1.27–2.37). The Ti–SBA-15 materials with Ti/Si ratios smaller than 0.05 were curved solid tubes, while those with the Ti/Si ratios between 0.05–0.1 possessed platelet morphology and short mesochannels (ca. 150–500 nm). Titanium was homogeneously distributed in the silica framework of the as-made Ti–SBA-15 materials as isolated Ti species when the Ti/Si ratios were lower than 0.03. It formed small TiO2 nanocrystallites when the Ti loading was further increased or after the materials were calcined at temperatures higher than 500 °C. It is noteworthy that tetrahedrally coordinated Ti(IV) species were generated on the superficial areas of SBA-15 silica framework upon calcination at 600–1000 °C. These tetrahedrally coordinated Ti(IV) species not only stabilized the mesopore ordering up to 950–1000 °C, but also acted as effective catalytic sites in cyclohexene epoxidation.

Hollow spheres of MCM-41 aluminosilicate with pinholes

Hollow spheres of MCM-41 mesoporous aluminosilicates, with two small holes on the shell, have been synthesized from a surfactant-aluminosilicate gel composite.

Hierarchical organization of mesoporous MCM-41 ropes

Millimeter long ropes of MCM-41 materials are made from micrometer-sized fibers by self-assembly and flow-induced orientation.

Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template

Mesoporous silica of high surface area, large pore size were readily prepared by using the bio-degradable gelatin as template and sodium silicate solution as silica source. Pore size of the mesoporous silica is dependent on the pH value of the hydrothermal solution. In addition, the gelatin-phenol formaldehyde polymer blend can also be used as the template to synthesize the mesoporous silica or mesoporous carbon via proper preparation processes.

The Synthesis and Characterization of Mesoporous Molecular Sieves MCM-41 with Interconnected Channels

Abstract The mesoporous MCM-41 materials with highly connected nanochannels have been obtained from the aluminosilicate-CnTMAX-H2O systems by a delayed neutralization procedure. The N2 adsorption-desorption isotherm of the materials exhibits a large type B hysteresis at p/p0 0.5. The hysteresis effect is dependent on the synthetic condition and the Si/Al ratio. In spite of the chain length of the surfactant, this hysteresis takes place around the same p/p0 value. From the TEM micrographs of the ultrathin section, one can clearly find that these mesoporous materials contain many structure defects, which are irregular shaped and the size distributes between 5.0-30.0 nm. Combining the above two evidences, we interpret the neighboring channels are interconnected through defects in channels walls. The diffusion of molecules inside these highly defective MCM-41 materials becomes more effective. We show that it leads to a better catalyst support material using ethylbenzene dehydrogenation reaction as an illustration.

Two-dimensional crystals of mesoporous silica SBA-15 nanosheets with perpendicular and open channels

A preparation of mesoporous silica SBA-15 thin sheets with perpendicular nanochannels (SBA(⊥)) and open ends is reported here. At a synthesis condition of pH = 2 where the silica condensation is extremely slow, micron-sized single-crystal-like hexagonally faceted nanosheets (SBA(⊥)-pH2) with aspect ratio of 10–50 were formed. The nanosheets can attach to each other in sideway to extend the thin sheet. At pH = 5, multi-domain SBA(⊥)-pH5 nanosheets are formed, and stacking attachment of sheets is preferred. Vivid Moire patterns are observed in large areas of stacked silica sheets, indicating excellent structure order.

A study on the synthesis of mesoporous silica and carbon platelets with perpendicular nanochannels

Free-standing mesoporous silica platelets in micron-scale consisting of perpendicular nanochannels were prepared with a ternary-surfactant composition of cationic, anionic and neutral block copolymer surfactants. The mesostructure of the mesoporous silica platelet(⊥) is templated by Pluronic 123 surfactant, and the platelet morphology is determined by the catanionic surfactant. The mesoporous silica platelet(⊥) was utilized as the nano-template to synthesize the mesoporous carbon platelet(⊥).