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-supportedcatalysts prepared by
catalytic activity of MCM-41 supportedcatalysts 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
], clays [ 15 ] and zeolites [ 13 ]. Application of alumina-supportedcatalysts in organic transformations has been receiving attention in recent years [ 16 , 17 ]. Immobilization of homogeneous transition metal catalysts to alumina carriers offers several
Authors:Jinxue Wang, Min Liu, Xinwen Guo, Hongyu Wu, Jun Xu, and Wenqi Lu
Previous work showed that only a narrow range size of Au particles delivered high PO selectivity on an Au supportedcatalyst [ 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
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.
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.
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.
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.
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.
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