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Reaction Kinetics, Mechanisms and Catalysis
Authors: Susana Pinto-Castilla, Santiago Marrero, Yraida Díaz, Joaquín L. Brito, Pedro Silva, and Paulino Betancourt

studied, in general, there was an increase in activity, the most remarkable one being that of the catalyst supported on activated carbon Riedel-de Haën (V/AC-RH). It is obvious that the hydrotreating activity over vanadium-supported catalysts prepared by

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catalytic activity of MCM-41 supported catalysts and described effect of these parameters on the selectivity by using a new parameter S P , called the isomerization selectivity parameter. The effective factors on the isomerization can be simply lumped into

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], clays [ 15 ] and zeolites [ 13 ]. Application of alumina-supported catalysts in organic transformations has been receiving attention in recent years [ 16 , 17 ]. Immobilization of homogeneous transition metal catalysts to alumina carriers offers several

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Previous work showed that only a narrow range size of Au particles delivered high PO selectivity on an Au supported catalyst [ 3 ]. According to Hayashi et al., an Au particle size smaller than 1.5–2 nm resulted in C 3 H 6 hydrogenation, while Au particles

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Nanopages
Authors: A. Szabo, A. Fonseca, L. P. Biro, Z. Konya, I. Kiricsi, A. Volodin, C. Van Hasendonck, and J. B.Nagy

Some recent results on the synthesis of coiled carbon nanotubes (CNTs) are summarized. Several supported catalysts can lead to the formation of coiled CNTs. Interestingly, certain domains of the coil pitch and coil diameter are favoured, and two “stability islands”are found in the 3D representation of the number of coiled CNTs as a function of both coil pitch and coil diameter. It is emphasized that these nanotubes are formed either by introducing pairs of five-membered ring - seven-membered ring or by forming haeckelite structures. The coiled CNTs could be used in nanocomposite reinforcement as well as special sensors based on their remarkable mechanical and electrical properties.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Nancy Martín, Alejandro López-Gaona, Margarita Viniegra, Patricia Villamil, and Gilberto Córdoba

Abstract  

Two mesoporous silicas (HMS) with high surface area and a pore diameter size of 2 nm were synthesized by a sol–gel method. Platinum catalysts were prepared with a 1 wt% metal content. A commercial silica supported catalyst was used for comparison. The catalysts were characterized by H2-TPR, TEM and 29Si-CP-MAS-NMR. The catalytic activity was measured by the hydrodechlorination of 1,2-dichloroethane. The enhanced activity of the mesoporous catalysts was related to the platinum particle size.

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Abstract  

A critical review of available data on the heats of chemisorption of gases at metals is given. The effect of upward technical and procedural trends on measured results is demonstrated. The results for surfaces approached to their states occurring in catalytic processes are accentuated. Several tens of chemisorbent/gas systems are considered; a number of the results are confirmed by several independent measurements. The coverage-independence of heats of chemisorption for powders, supported catalysts, components of multi-component catalysts, and films is demonstrated; the better the techniques and procedures, the closer to zero the angle between the heat-coverage function and the abscissa. The principal conclusion on surface homogeneity of stabilized surfaces is made.

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Supported catalysts contain often only small amounts of active component(s) which renders their characterization difficult, particularly because they usually contain a substantial amount of water. Thermal analysis (TA) coupled with mass spectrometry (MS) offers an interesting potential for characterizing such material, various steps of catalyst preparation as well as crucial properties of fresh and used catalysts can be investigated. Some examples illustrating the versatility of TA-MS in catalysis research, such as solid-state reactions occurring upon exposure of the precursors or catalysts to reducing, oxidizing or inert atmosphere, are presented in this study. The combined use of TA and MS allows in many cases a much more detailed interpretation of the observed phenomena than could be achieved by one of these methods alone.

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Abstract  

The catalytic performance of unsupported and carbon-supported Fe, Mo and Fe−Mo catalysts for Fischer-Tropsch synthesis is greatly influenced by the final reduction states of the catalysts. In this investigation, the reduction process of the catalysts by H2 was studied by using TG-DTG. The reduction process depends not only on the reducibility of metals but also on the nature of the support. Methanation of the support occurred as soon as the supported metals were completely reduced for the carbon-supported catalysts. For these, the reduction temperature should by carefully selected so that the metal oxides are reduced as completely as possible, whilst the methanation of the support must be avoided to obtain optimum reduced catalysts.

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Abstract  

The quantitative interpretation of X-ray fluorescence (XRF) data is often difficult because of matrix effects. The intensity of fluorescence measured for a given element is not only dependent on the element's concentration, but also on the mass absorption coefficients of the sample for the excitation and fluorescence radiation. Also, there are interelement effects in which high-energy fluorescence from heavier elements is absorbed by ligher elements, with a resulting enhancement of their fluorescence. Recent theoretical treatments of this problem have shown that X-ray fluorescence data can be corrected for these matrix effects by calculations based on first principles. Fundamental constants, available in atomic physics data tables, are the only parameters needed. It is not necessary to make empirical calibrations. In this paper we report the application of this correctional procedure to alloys and alumina-supported catalysts. We also discuss how it may be applied to other matrices. A description is given of a low-background spectrometer which uses monochromatic AgKα radiation for excitation. Matrix corrections by first principles can be easily applied to data from instruments of this type because fluorescence excitation cross-sections and mass absorption coefficients can be accurately defined for monochromatic radiation.

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