Fischer-Tropsch Catalysts Based on Zr-Fe Intermetallides Encapsulated in an Al2O3/Al Matrix

ZrFe and ZrFe₂ intermetallides in an Al₂O₃/Al cermet matrix are reported as catalysts for the fixed-bed Fischer-Tropsch synthesis, and the effects of some preparation conditions on their texture, structural, mechanical, and catalytic properties are discussed. A nonmonotonic dependence of their catalytic activity on the size of interametallide particles is observed. The selectivity, activity, and mechanical strength of the composites depend on the calcination temperature and on the place of the hydriding step in the catalyst preparation procedure. In terms of volumetric efficiency, the catalysts prepared are comparable with bulk, unencapsulated intermetallides and are among the most efficient iron-containing catalysts known to date.     

Direct synthesis of nitrogen-containing filamentous carbon on a high-percentage Ni-Cu catalyst

Nitrogen-containing catalytic filamentous carbon (N-CFC) of chemical composition NC₁₈-NC₁₀₄ has been synthesized by the decomposition of pyridine (Py) from gaseous mixtures with argon or H₂ at 550–800°C on Ni/Al₂O₃ (Ni) and Ni-Cu/Al₂O₃ (Ni-Cu) high-percentage catalysts. The activity of the Ni-Cu catalyst in Py decomposition in mixtures with H₂ is about one order of magnitude higher than its activity in Py/Ar mixtures (more than 70 g N-CFC per metal gram in 4.5 h at 750°C), which is interpreted as arising from the nickel-catalyzed hydrogenation of Py. The formation and growth of carbon fibers occurs through the decomposition of Py (from Ar/Py mixtures) and/or Py hydrodenitrification products (from H₂/Py mixtures). The carbon material has been characterized by elemental analysis, low-temperature nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The effect of the noncatalytic reactions of Py and its transformation products on the composition and texture of N-CFC is discussed.     

Analysis of the drying stage in the technology of supported catalysts

The distribution of the precipitated active component has been analyzed using the concepts of moisture transfer mechanism for the evaporation of porous materials. Formulas are proposed for the low-dispersity phase, depending on the precipitation parameter. The calculations performed using a statistical porous environment model are in reasonable agreement with the experimental data.

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Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Comparative analysis of isotherms of water vapor adsorption on oxides

Comparative method is suggested for the analysis of water vapor adsorption on the partially dehydroxylated surface of Si, Al, Ti, Zn, etc., oxides. The method removes distortions typical of BET method, usually employed here, allows to calculate correctly the surface area and values of specific adsorption due to the change of surface hydroxy coverage.     

Carbon Dispersion and Morphology in Carbon-Mineral Adsorbents

Carbon-mineral composite adsorbents prepared by deposition of carbon on various mineral supports have been studied extensively by a new textural approach. The evidence of significant influence of both organization of initial mineral support porous space and mobility of carbon precursors over the surface of mineral support on carbon localization has been obtained. Restricted mobility of carbon precursors leads to homogeneous distribution of carbon clusters over the support surface despite the presence of narrow mesopores in the structure of the support if the entire support surface is equiaccessible. Unrestricted mobility over the smooth surface of the mineral support without narrow mesopores leads to the similar resulting carbon distribution. However, unrestricted mobility of carbon precursors in densely packed porous materials seems to be the reason for carbon pulling and deposition in narrow mesopores. These peculiarities of carbon deposition influence the carbon/mineral (hydrophobic/hydrophilic) composition of the composite surface. Trapping of carbon in narrow mesopores leads to a decrease and, in contrast, homogeneous dispersion of carbon over the whole support surface leads to an increase in the part of the composite surface, which can be appropriated to carbon. Copyright 2000 Academic Press.     

Mesoporous “core-shell” adsorbents and catalysts with controllable morphology

A simple geometrical model is applied to predict the thickness of mesoporous shells over monodisperse spherical particles. As an example, mesoporous Ti-silicate nearly monodisperse particles with the “core-shell” structure, synthesized via the one-pot procedure are considered. The unique features of the materials are orientation of mesopores perpendicularly to the surface of non-porous cores and uniformity of mesoporous shells structure and thickness. This allows considering these materials as interesting catalysts for partial oxidation of bulk organic molecules with hydrogen peroxide.     

Study of surface structure of catalytic carbon filaments by secondary ion mass-spectroscopy

The SIMS method has been used for studying the time dependent intensities of the secondary ions H₂O⁺, O⁺, CH ₃ ⁺ and C⁺ under Ar⁺ bombardment of two CCF samples with different packing of filaments. The thickness of defect layers is estimated from the median of secondary ions distribution.     

Direct contact free real-time acquisition of temperature profiles in adsorbent bed during vacuum swing adsorption

Real-time temperature co-axial profiles in a bed of mesoporous alumosilicate were recorded by means of FPA-based infrared thermography during air drying vacuum swing adsorption cycles. The good correlation between experimentally measured temperature profiles and profiles simulated on the basis of linear driving force model of mass and heat transfer in nonadiabatic regime is observed.     

Calculation of pore size from adsorption data

Spherical pores (voids) with 1 to 6 round necks are used to estimate the probable disagreement between the average diameter and Kelvin equivalent size. This disagreement is due to the delay in irreversible capillary condensation in such pores [1, 2].