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Pore Mouth (pore + mouth)
Selected AbstractsPerformance study of modified ZSM-5 as support for bimetallic chromium,copper catalysts for VOC combustionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2004Ahmad Zuhairi Abdullah Abstract The catalytic performance of bimetallic chromium,copper supported over untreated ZSM-5 (CrCu/Z), ZSM-5 treated with silicon tetrachloride (Cr,Cu/SiCl4 -Z) and ZSM-5 treated with steam (Cr,Cu/H2O-Z) is reported. The activity is based on the combustion of ethyl ethanoate and benzene at a feed concentration of 2000 ppm and a gas hourly space velocity (GHSV) of 32 000 h,1. Due to higher reactivity and larger molecular size compared with that of water molecules, SiCl4 reacted at the external surface of ZSM-5 crystals. Cr,Cu/SiCl4 -Z and Cr,Cu/H2O-Z both gave slightly lower conversion and carbon dioxide yield compared with Cr,Cu/Z. This was attributed to larger active metal crystallites formed in the mesopores and narrowing pore mouth and pore intersection by extraframework species. Cr,Cu/SiCl4 -Z and Cr,Cu/H2O-Z both had reduced concentration and strength of acid sites, thus making them less susceptible to deactivation by coking. The coke accumulated by these two catalysts was relatively softer and more easily decomposed in oxygen during catalyst regeneration. Copyright © 2004 Society of Chemical Industry [source] The High-Temperature Oxidation Behavior of Reaction-Bonded Porous Silicon Carbide Ceramics in Dry OxygenJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Chuanwei Zheng The oxidation behavior of reaction-bonded porous silicon carbide (RPSC) ceramics in dry oxygen between 1100° and 1500°C was investigated based on four specimens with different porosities. RPSC ceramics exhibited a rapid mass increase in the initial stage of oxidation but a slow mass increase in the following oxidation, which was considerably different from the oxidation behavior of dense SiC. The oxidation kinetics for RPSC can be better represented by an asymptotic law rather than the parabolic law for dense SiC. We suppose that, although oxidation occurred in the entire pore channels at the beginning, the pores were rapidly blocked by the oxide as their growth rate near the pore mouth was very fast due to sufficient oxygen. As the result, the oxidation of the pore interior was stopped in the absence of further oxygen supply. [source] Consideration of the Effect of Irregular Catalytic Active Component Distributions in Mesopores , Extension of a Model for Wall Catalyzed Reactions in Microchannel ReactorsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2003B. Platzer Abstract Data available from the literature and experimental results have shown that the distribution of the catalytic active components can be irregular already for fresh catalysts. The determination of the local concentrations of the catalytic active components using wavelength dispersive X-ray spectroscopy confirms this for microstructured wafers used in microchannel reactors. Considering this nonuniform distribution, the used model gives the relation between the local concentration profiles of the reactants inside the pores and the product yield in the entire pore. These results were used in an equation for the diffusion flux at the pore mouth, which is useful for a microchannel model developed in a recent paper [1]. The theoretical considerations deal with cylindrical pores with known reactant concentrations at the pore mouth and known distribution of the catalytic active component within the pore. Beside numerical results, some analytical solutions with low mathematical expense, applicable to special cases, are discussed. The nonconsideration of the irregular distribution of the catalytic active component can be the reason for difficulties during the extrapolation of experimental results to slightly different conditions and can have a great influence on the reaction results. The regarded examples are typical of wall-catalyzed reactions in microchannel reactors with mesopores. [source] Accessibility of simple gases in disordered carbons: theory and simulationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009T. X. Nguyen Abstract We present a review of our recent studies on the accessibility of simple gases (Ar, N2, CH4 and CO2) in disordered microporous carbons using transition state theory (TST) and molecular simulation techniques. A realistic carbon model rather than the slit-pore approximation is utilised, providing more accurate understanding of complex adsorption equilibrium and dynamics behaviour at the molecular level in porous carbons, especially kinetic restriction of adsorbate molecules through highly constricted pore mouths of coals and molecular sieve carbons (MSC). This kinetic restriction leads to a molecular sieving effect which plays a vital role in gas separation using the MSCs. In particular, the realistic carbon model of a saccharose char used in a recent study was obtained by hybrid reverse Monte Carlo simulation. The time of adsorption or desorption of the single gas molecule between two neighbouring pores through a highly constricted window of the realistic saccharose char model was determined using TST. Finally, the validation of TST calculated results of adsorption and desorption times against experimental measurements as well as molecular dynamics simulation is also presented in this article. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||