Hydrothermal stability and catalytic activity of aluminum-containing mesoporous ethane-silicas

Aluminum was incorporated into the mesoporous framework of ethane-silica by one-pot condensation of Al(OiPr)(3) with 1,2-bis(trimethoxysilyl)ethane using octadecyltrimethylammonium chloride as surfactant. Powder X-ray diffraction patterns, nitrogen sorption analysis, and TEM results reveal the formation of an ordered mesoporous material with uniform porosity. Al-27 MAS NMR confirms the incorporation of aluminum in the framework. The synthesized materials exhibit extremely high hydrothermal stability in boiling water (no obvious change of mesostructure and textural properties was observed even after refluxing in water for 100 h), which could be mainly contributed to the ethane-bridged mesoporous framework. The aluminum-containing mesoporous ethane-silicas are efficient catalysts for the alkylation of 2,4-di-tert-butylphenol by cinnamyl alcohol to yield a flavan.

Solid-state MAS NMR studies on the hydrothermal stability of the zeolite catalysts for residual oil selective catalytic cracking

By using the solid-state MAS NMR technique, the hydrothermal stabilities (under 100% steam at 1073 K) of HZSM-5 zeolites modified by lanthanum and phosphorus have been studied. They are excellent zeolite catalysts for residual oil selective catalytic cracking (RSCC) processes. It was indicated that the introduction of phosphorus to the zeolite via impregnation with orthophosphoric acid led to dealumination as well as formation of different Al species, which were well distinguished by Al-27 3Q MAS NMR. Meanwhile, the hydrothermal stabilities of the zeolites (P/HZSM-5, La-P/HZSM-5) were enhanced even after the samples were treated under severe conditions for a prolonged time. It was found that the Si-O-Al bonds were broken under hydrothermal conditions, while at the same time the phosphorous compounds would occupy the silicon sites to form (SiO)(x)Al(OP)(4 - x) species. With increasing time, more silicon sites around the tetrahedral coordinated Al in the lattice can be replaced till the aluminum is completely expelled from the framework. The existence of lanthanum can partially restrict the breaking of the Si-O-Al bonds and the replacement of the silicon sites by phosphorus, thus preventing dealumination under hydrothermal conditions. This was also proved by P-31 MAS NMR spectra. (C) 2004 Elsevier Inc. All rights reserved.

Photocatalytic water reduction under visible light on a novel ZnIn2S4 catalyst synthesized by hydrothermal method

A novel ZnIn2S4 catalyst synthesized by hydrothermal method shows high and stable photocatalytic activity for water reduction under visible light illumination.

On configuration of exchanged La3+ on ZSM-5: A theoretical approach to the improvement in hydrothermal stability of La-modified ZSM-5 zeolite

Density functional calculations have been employed to investigate the locating and binding of lanthanum cation, i.e., La(OH)(2)(+), on HZSM-5 zeolite. Through geometry optimization, it was determined that lanthanum ions are favorably accommodated in the two 6-T rings of the straight channels (Clusters 1 and 2, see Sec. III A for details). Cluster 1 was found to exist in prior to Cluster 2 due to the preference of Al substitution in the T11 site (Cluster 1) rather than in the T8 site (Cluster 2). Geometry-optimization of Cluster 1 containing another two lanthanide ions Nd3+ and Yb3+ was also carried out and it was found that a monotonic decrease in Ln-O bond length will take place as the atomic number increases, conforming well to the rule of lanthanide contraction. Some of the optimized parameters are comparable to the corresponding experimental values in Y zeolite, which confirms that the optimized configurations are acceptable. The average frequencies of hydroxyls attached to La3+ or Yb3+ in Cluster 1 fall at 3609.16 and 3579.76 cm(-1), respectively, with the gap of these two frequencies close to that in the sodalite cage of Y zeolite. Compared to H-form zeolite, the charges on both Al and O atoms in Ln-ZSM-5 zeolite show an obvious increase, which will undoubtedly lead to a stronger mutual interaction and hence enhance the stability of the [AlO4](-) anion. Moreover, the Ln(OH)(2)(+) seem to have thickened the zeolite framework, which can effectively retard the process of dealumination. Through the evaluation of the possibility for dimer formation, it turned out that when the exchange degree arrived to approximately 0.28, lanthanum monomers began to aggregate into dimers, and were completely converted into dimers when the exchange degree approached 0.60. (C) 2003 American Institute of Physics.

Preparation and Characterization of BaLiF3:Er3+ Nanoparticles by the Hydrothermal Microemulsion Synthesized Method

Nanoparticles of BaLiF3:Er3+ were prepared from the quaternary microemulsions of Cetyltrim-Enthyl Ammonium Bromide (CTAB), n-butanol, n-octane, and water, using the hydrothermal-microemulsion technique. The complex fluorides were characterized by means of X-ray power diffraction, Environmental Scanning Electron Microscopy (ESEM), and fluorescence spectra.

Hyperbranched polymer-assisted hydrothermal in situ synthesis of submicrometer silver tubes

We produced silver tubes with an outer diameter of 1 mu m, wall thickness of 200 nm, and length of hundreds of micrometers by hydrothermal treatment of aqueous solutions of AgNO3 and hyperbranched polyglycidol (HPG) at 165 degrees C. The surfaces of the silver tubes were chemically modified by HPG, which was confirmed by FTIR of the silver tubes.

Hydrothermal Synthesis and High Photocatalytic Activity of 3D Wurtzite ZnSe Hierarchical Nanostructures

Novel 3D wurtzite ZnSe hierarchical nanostructures have been synthesized by a mild hydrothermal treatment. The as-prepared flowerlike nanostructures efficiently catalyze the photodegradation of methylene blue and ethyl violet present in aqueous solutions under UV light irradiation, exhibiting higher photocatalytic activity than the commercially available photocatalysts P25 and ZnSe microspheres. We also demonstrate that flowerlike morphology is important for the excellent photocatalytic activity.

Hydrothermal synthesis and thermoelectric transport properties of impurity-free antimony telluride hexagonal nanoplates

Impurity-free single-crystalline antimony telluride hexagonal nanoplates (see figure) are synthesized by a facile and quick hydrothermal treatment without any organic additives or templates. The inherent crystal structure is the driving force for the growth of these Sb2Te3 hexagonal nanoplates. Films of these nanoplates shows p-type behavior, and exhibit a promisingly high Seebeck coefficient of 425 mu V K-1 at room temperature.

Hydrothermal synthesis and photoluminescent properties of stacked indium sulfide superstructures

Unusual hierarchical stacked superstructures of cubic beta-In2S3 were fabricated via a facile hydrothermal process in the presence of a surfactant cetyltrimethylammonium bromide CTAB; the 3D superstructures were developed by helical propagation of surface steps from microflakes of 10-20 nm thickness.

Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe-Co/CoFe2O4 nanocomposite and CoFe2O4 nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature.