Showing papers by "Zi Gao published in 2003"

General synthesis of mesoporous spheres of metal oxides and phosphates.

Abstract: Monodisperse and high-surface-area mesoporous inorganic spheres of various compositions including metal oxides, mixed oxides, and metal phosphates are prepared by templating mesoporous carbon spheres which are replicated from spherical mesoporous silica. Due to the rigid and thermally stable framework of carbon template, the crystalline phases of the obtained metal oxide spheres can be readily tailored by controlling crystalline temperatures. Moreover, the sphere morphologies can be changed from solid structure to hollow structure in some cases by changing the polarity of the precursor, due to the hydrophobic nature of carbon template.

Preparation of Hollow Zeolite Spheres and Three-Dimensionally Ordered Macroporous Zeolite Monoliths with Functionalized Interiors

Abstract: A novel and flexible strategy involving hydrothermal transformation of guest-incorporated zeolite-seeded mesoporous silica spheres was proposed to prepare guest-encapsulated hollow zeolite spheres and three-dimensionally (3D) ordered macroporous zeolite monoliths. The guest species that were pre-incorporated into the mesopores of silica spheres could be spontaneously encapsulated inside the formed hollow zeolite shells by consuming silica nutrition of the original mesoporous silica cores during the hydrothermal process. A wide range of guest materials with a size ranging from nanometers to micrometers, e.g., Ag and PdO nanoparticles, and mesoporous spheres of carbon and polymer of micrometer size were successfully encapsulated into both discrete hollow zeolite spheres and 3D ordered macroporous zeolite monoliths. Such materials are expected to find a variety of applications such as catalysis, adsorption, and novel microreactors for their special structures with active species inside and zeolitic porous shell outside.

Selective oxidation of styrene over nanosized spinel-type MgxFe3−xO4 complex oxide catalysts

Abstract: Nanosized spinel-type MgxFe3−xO4 complex oxide catalysts were prepared by coprecipitation and citrate gel methods and were characterized. The crystallization temperature of spinel particles prepared by citrate gel method is about 300 °C lower than that of those prepared by coprecipitation method. MgxFe3−xO4 catalysts prepared by citrate gel method have higher dispersity and smaller particle size, leading to higher activity for styrene oxidation with H2O2 as oxidant. The nonstoichiometric MgxFe3−xO4 catalysts (x

Nanosized titania and zirconia as catalysts for hydrolysis of carbon disulfide

Abstract: Nanosized titania and zirconia were prepared by different ways and used as catalysts for CS 2 hydrolysis. The hydrolysis activity of the nanosized oxide catalysts is much higher than that of commercial nanosized γ-Al 2 O 3 with comparable specific surface area and grain size. The temperatures of 90% conversion of CS 2 ( T 90 ) on nanosized titania and zirconia are 210 and 205 °C, respectively, which are 130–135 °C lower than that on γ-Al 2 O 3 . CO 2 -TPD, TG and IR studies show that the enhanced activity is due to reduced surface hydrophilicity and increased free surface basic hydroxyl groups on the catalysts. The presence of potassium as a promoter on titania catalyst increases its hydrolysis activity, but the promoted catalyst deactivates faster on stream due to catalyst sulfation caused by a trace amount of O 2 impurity in the feed.

Hydrothermal Conversion of Solid Silica Beads to Hollow Silicalite-1 Sphere

Abstract: Uniform hollow silicalite-1 spheres with a high intact ratio and good mechanical stability were fabricated through a novel and effective approach, which involved the seed-induced hydrothermal crystallization of mesoporous silica microbeads in an alkaline aqueous solution.

n-Butane isomerization over Cs-salts of H3PW12O40: a mechanistic study by 1C MAS NMR

Abstract: Reaction mechanism of skeletal isomerization of n-butane over Cs2.5H0.5PW12O40 catalyst was studied using 13 C MAS NMR. The reaction proceeds mainly via a monomolecular mechanism at 80 °C. The contribution of the bimolecular mechanism becomes more significant as the reaction temperature is increased to 150 °C. Hydrogen suppresses the bimolecular mechanism, in particular on Pt-promoted Cs2.5H0.5PW12O40 catalyst. The latter catalyst is highly selective to isobutane in the presence of H2 even at 220 °C. The kinetics of the monomolecular isomerization reaction and the reaction schemes of 13 C scrambling and n-butane isomerization are discussed.

Support effect in hydrogenation of methyl benzoate over supported manganese oxide catalysts

Abstract: Manganese oxide supported on MgO, γ-Al 2 O 3 , SiO 2 , ZrO 2 , TiO 2 and SiO 2 -Al 2 O 3 catalysts were prepared. The effect of support on their catalytic behavior for hydrogenation of methyl benzoate to benzaldehyde was studied. The formation of toluene is suppressed on the supported catalysts due to the dilution of oxygen vacancies on the catalyst surface. The benzaldehyde yield of the supported catalysts follows the trend Mn/γ-Al 2 O 3 >Mn/TiO 2 >Mn/ZrO 2 >Mn/SiO 2 -Al 2 O 3 >Mn/SiO 2 >Mn/MgO. XRD measurements show that the Mn nitrate precursor is essentially transformed to highly dispersed MnO 2 on the supports at calcination and subsequently to MnO under reaction conditions with an exception of Mn/MgO. TPR and XPS analyses suggest that a strong interaction between manganese oxide and the γ-Al 2 O 3 support plays a positive role in the hydrogenation reaction.

Mesoporous alumina molecular sieves: characterization and catalytic activity in hydrolysis of carbon disulfide

Abstract: Mesoporous MSU-X alumina molecular sieves were synthesized through the neutral N0I0 assembly pathway using aluminum sec-butoxide as the precursor and a triblock poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) as the structure-directing agent. Their surface acidity and basicity as well as textural properties were characterized by NH3-TPD, CO2-TPD, IR spectroscopy and N2 adsorption methods. The materials are abundant in surface weak acid sites and weak-medium basic sites. They are more active than the commercial γ-Al2O3 catalyst for the CS2 hydrolysis reaction, and the temperature of 90 conversion of CS2 on the mesoporous alumina is 130K lower than that of γ-Al2O3.