CO hydrogenation to light alkenes over Mn/Fe catalysts prepared by coprecipitation and sol-gel methods

CO hydrogenation to light alkenes was carried out on manganese promoted iron catalysts prepared by coprecipitation and sol-gel techniques. Addition of manganese in the range of 1-4 mol.% by means of coprecipitation could improve notably the percentage of C-2 (=) similar to C-4 (=) in the products, but it was not so efficient when the sol-gel method was employed. XRD and H-2-TPR measurements showed that the catalyst samples giving high C-2 (=) similar to C-4 (=) yields possessed ultra. ne particles in the form of pure alpha-(Fe1-xMnx)(2)O-3, and high quality in lowering the reduction temperature of the iron oxide. Furthermore, these samples displayed deep extent of carburization and different surface procedures to the others in the tests of Temperature Programmed Surface Carburization (TPSC). The different surface procedures of these samples were considered to have close relationship with the evolving of surface oxygen. It was also suggested that for the catalysts with high C-2 (=) similar to C-4 (=) yields, the turnover rate of the active site could be kept at a relatively high level due to the improved reducing and carburizing capabilities. Consequently, there would be a large number of sites for CO adsorption/dissociation and an enhanced carburization environment on the catalyst surface, so that the process of hydrogenation could be suppressed relatively to a low level. As a result, the percentage of the light alkenes in the products could be raised.

Sol-gel synthesis and electrical properties of ceria-based solid electrolytes

A series of solid electrolytes (Ce0.8RE0.2)(1-x)MxO2-delta(RE: Rare earth, M: Alkali earth) were prepared by sol-gel methods. XRD indicated that a pure fluorite phase was formed at 800 degrees C. The synthesis temperature by the sol-gel methods was about 700 degrees C lower than by the traditional ceramic method. The electrical conductivity and impedance spectra were measured. XPS showed that the oxygen vacancy increased obviously by doping MO, thus, resulting in the increase of the oxygen ionic transport number and conductivity. The performance of ceria-based solid electrolyte was improved. The effects of RE2O3 and MO on the electrical properties were discussed. The conductivity and the oxygen ionic transport number of (Ce0.8Sm0.2)(1-0.05)Ca0.05O2-delta is 0.126 S.cm(-1) and 0.99 at 800 degrees C, respectively.

COMPARATIVE-STUDY OF CA4Y6(SIO4)(6)O-A PHOSPHORS PREPARED BY SOL-GEL AND DRY METHODS (A=PB2+,EU3+, TB3+,DY3+)

Ca4Y6(SiO4)(6)O:A (A = Pb2+, Eu3+, Tb3+, Dy3+) phosphors have been prepared by two methods: the sol-gel method and the conventional dry method. The crystallization processes and the luminescence characteristics of the phosphors were studied, The sol-gel method features low-temperature formation of the phosphor, leading to successful preparation of Pb2+-activated phosphors which could not be prepared by the dry method at high temperature. The (4f)(8-)(4f)(7)(5d)(1) absorption band of Tb3+ and the charge-transfer (CT) band of Eu3+ have higher energies and narrower half-widths in the sol-gel-derived phosphors than in the phosphors prepared by the dry method, respectively. The Tb3+ and Dy3+ ions show stronger emission in the former than in the latter. Both the yellow-to-blue intensity ratio (Y:B) of Dy3+ and the red-to-orange intensity ratio (R:O) of Eu3+ in the sol-gel-derived phosphors are smaller than those for the phosphors derived by the dry method.

Synthesis of CaCu3Ti4O12 ceramic via a sol-gel method

The novel nano-ultrafine powders for the preparation of CaCu3Ti4O12 ceramic were prepared by the sol-gel method and citrate auto-ignition method. The obtained precursor powders were pressed, sintered at 1000 degrees C to fabricate microcrystal CaCu3Ti4O12 ceramic. The microcrystalline phase of CaCu3Ti4O12 was confirmed by X-ray powder diffraction (XRD). The morphology and size of the grains of the powders and ceramics under different heat treatments were observed using scanning electron microscopy (SEM). The relative dielectric constant of the ceramic sintered at 1000 degrees C was measured with a magnitude of more than 10(4) at room temperature, which was approaching to those of Pb-containing complex perovskite ceramics, and the loss tangent was less than 0.20 in a broad frequency region. The relative dielectric constant and loss tangent were also compared with that of CaCu3Ti4O12 ceramic prepared by other reported methods. (c) 2006 Elsevier B.V. All rights reserved.

Preparation of stir bars for sorptive extraction using sol-gel technology

A sol-gel coating method for the preparation of extractive phase on bars used in sorptive microextraction is described. The extraction phase of poly(dimethylsiloxane) is partially crosslinked with the sol-gel network, and the most part is physically incorporated in the network. Three aging steps at different temperatures are applied to complete the crosslinking process. Thirty-micrometer-thick coating layer is obtained by one coating process. The improved coating shows good thermal stability up to 300degreesC. Spiked aqueous samples containing n-alkanes, polycyclic aromatic hydrocarbons and organophosphorus pesticides were analyzed by using the sorptive bars and GC. The results demonstrate that it is suitable for both aploar and polar analytes. The detection limit for chrysene is 7.44 ng/L, 0.74 ng/L for C-19 and 0.9 ng/L for phorate. The extraction equilibration can be reached in less than 15 min by supersonic extraction with the bars of 30 mum coating layer. (C) 2004 Elsevier B.V. All rights reserved.

Polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers. 1. Morphology of poly(butyl methacrylate)/SiO2

In this article, we report on an approach of using an emulsion polymerized polymer in preparing organic-inorganic nanocomposites through a sol-gel technique. By mixing a polymer emulsion with prehydrolyzed tetraethoxysilane transparent poly(butyl methacrylate)/SiO2, nanocomposites were prepared as shown by TEM. AFM, FTIR, and XPS results show that there is a strong interaction between polymer latex particles and the SiO2 network. Comparison of the emulsion method with a traditional solution method shows that nanocomposites can be prepared by both methods, but there is some difference in their morphology and properties.

Fabrication and electrochemical behavior of a sol-gel-derived carbon ceramic composite electrode entrapping 2 : 18-molybdodiphosphate

A new type of inorganic-organic hybrid material incorporating carbon powder and alpha -type 2:18-molybdodiphosphate (P2Mo18) in a methyltrimethoxysilane (MTMOS) based gel has been produced by a sol-gel process and used to fabricate a chemically modified electrode. The P2Mo18-doped carbon ceramic composite electrode was characterized using SEM and cyclic voltammetry. Square-wave voltammetry with an excellent sensitivity was exploited to conveniently investigate the dependence of current and half-wave potential (E-1/2) on pH. The chemically modified electrode has some advantages over the modified film electrodes constructed by the conventional methods, such as long-term stability, reproducibility, and especially repeatability of surface-renewal by simple polishing in the event of surface fouling or dopant leaching. In addition, the modified electrode shows a good catalytic activity for the electrochemical reduction of bromate in an acidic aqueous solution. (C) 2000 Elsevier Science B.V. All rights reserved.

Progress in luminescent films prepared by sol-gel process

In this paper, state of the art for luminescent films prepared by sol-gel process has been reviewed. The basic process and characteristics for the synthesis of luminescent films via sol-gel method, Characterization methods for the films and the current status for the development and application of luminescent films are discussed in the context, An elucidation has been made on the luminescent films classified by composition, including inorganic luminescent films and organic/inorganic hybrid luminescent films. The sol-gel derived luminescent films have found applications in the display devices for photoluminescence, electroluminescence, cathodoluminescence and field emission etc. Finally, the future development tendency for the luminescent films are forecasted.

Piezoelectricity Of Zno Films Prepared By Sol-Gel Method

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d(33) was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d(33) changes little and ultimately keeps constant at a low frequency.

Piezoelectricity of ZnO films prepared by sol-gel method

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d(33) was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d(33) changes little and ultimately keeps constant at a low frequency.

Sensitivity to alcohols of a planar waveguide ring resonator fabricated by a sol-gel method

A planar waveguide ring resonator was fabricated by organic-inorganic hybrid sol-gel materials; its sensitivity to ethanol vapor was experimentally investigated. It was found that dips in the transmission spectrum of the device shifted to longer wavelengths with increasing the ethanol concentration, and its sensitivity showed a linear relation with the ethanol concentration, showing a coefficient of 1.13 pm/ppm. In addition, the transmission loss of the ring resonator decreased with increasing the ethanol concentration. The measured characteristics suggest that the device may be considered as one of the candidates of alcohol vapor sensors. (c) 2006 Elsevier B.V. All rights reserved.