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Smaller Pore Size (smaller + pore_size)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Multilayer Amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 Membranes for Hydrogen Purification,,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Ravi Mohan Prasad
Abstract The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H2 can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single-step under high temperature conditions. In the present work, the multilayer amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H2/CO permeance. The ,-Al2O3 support has a bimodal pore-size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate ,-Al2O3 layer,deposited from boehmite colloidal dispersion,has an average pore-size of 8,nm being mesoporous. The results obtained by the N2 -adsorption method indicate a decrease in the volume of micropores,0.35 vs. 0.75,cm3,g,1,and a smaller pore size ,6.8 vs. 7.4 Å,in membranes with the intermediate mesoporous ,-Al2O3 layer if compared to those without. The three times Si-B-C-N coated multilayer membranes show higher H2/CO permselectivities of about 10.5 and the H2 permeance of about 1.05,×,10,8 mol m,2 s,1 Pa,1. If compared to the state of the art of microporous membranes, the multilayer Si-B-C-N/,-Al2O3/,-Al2O3 membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high-temperature and high-pressure stability. [source]

Activity of samarocene catalysts adsorbed on mesoporous silicates for the polymerization of methyl methacrylate

POLYMER INTERNATIONAL, Issue 11 2004
Dr Hajime Yasuda
Abstract A samarocene complex, (C5Me5)2SmMe(thf), was adsorbed on a series of mesoporous silicates of various pore sizes. Pre-treatment of the latter with AlMe3 before adding the complex was effective in deactivating the surface silanol functionalities. The silicates having relatively larger pore size tended to adsorb a larger amount of the complex. The polymerization of methyl methacrylate (MMA) by the complex adsorbed on the silicates with large pore sizes (>29 Å) quantitatively afforded highly syndiotactic poly(MMA)s with higher molecular weights compared with those obtained by the corresponding homogeneous system. Similar catalyst systems of smaller pore size were much less active. Copyright © 2004 Society of Chemical Industry [source]

Analyses of preservatives by capillary electrochromatography using methacrylate ester-based monolithic columns

ELECTROPHORESIS, Issue 18-19 2004
Hsi-Ya Huang
Abstract Five common food preservatives were analyzed by capillary electrochromatography, utilizing a methacrylate ester-based monolithic capillary as separation column. In order to optimize the separation of these preservatives, the effects of the pore size of the polymeric stationary phase, the pH and composition of the mobile phase on separation were examined. For all analytes, it was found that an increase in pore size caused a reduction in retention time. However, separation performances were greatly improved in monolithic columns with smaller pore sizes. The pH of the mobile phase had little influence on separation resolution, but a dramatic effect on the amount of sample that was needed to be electrokinetically injected into the monolithic column. In addition, the retention behaviors of these analytes were strongly influenced by the level of acetonitrile in the mobile phase. An optimal separation of the five preservatives was obtained within 7.0 min with a pH 3.0 mobile phase composed of phosphate buffer and acetonitrile 35:65 v/v. Finally, preservatives in real commercial products, including cold syrup, lotion, wine, and soy sauces, were successfully determined by the methacrylate ester-based polymeric monolithic column under this optimized condition. [source]

Gadolinium(III)-Loaded Nanoparticulate Zeolites as Potential High-Field MRI Contrast Agents: Relationship Between Structure and Relaxivity

CHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2005
Éva Csajbók Dr.
Abstract The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+ -loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+ -loaded cavities did not change significantly, which suggests that the windows of the Gd3+ -loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+ -loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+ -doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields. [source]