Influence of the operating conditions on the production rate of multi-walled carbon nanotubes in a CVD reactor

in Carbon (2004), 42(8-9), 1473-1482

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the ... [more ▼]

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the reaction rate to be inferred from the exhaust gas composition measurements. The tested reactor operating variables are the length and thickness of the catalytic bed, the total feed flow and the molar fraction of hydrocarbon in the feed. The results of the study are analyzed using well known reactor engineering models, which allows the origin of the observed physical limitations to be ascertained. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

Magnetic, Mössbauer spectral and nonlinear optical properties of ferric nanoparticle-doped silica xerogels

Conference (2004)

Improvement of metal dispersion in Pd/SiO2 cogelled xerogel catalysts

Poster (2004)

Pd-Ag catalysts supported on porous carbon xerogels for selective hydrodechlorination of 1,2-dichloroethane into ethylene

Poster (2004)

Palladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene - IV. Deactivation mechanism and regeneration

in Journal of Catalysis (2003), 220(1), 215-225

The activity and selectivity of a 1.9% Pd-3.7% Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene have been followed in the course of time. The deactivation curves ... [more ▼]

The activity and selectivity of a 1.9% Pd-3.7% Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene have been followed in the course of time. The deactivation curves show two distinct periods: an initial period at the very beginning of catalyst operation, that is, during the first 20 operating hours, characterized by a sharp decrease of the rates of both reactions involved in the process (1,2-dichloroethane hydrodechlorination and undesired ethylene hydrogenation) and a second period, after the first 20 operating hours and investigated for more than 600 h, characterized by a clearly slower deactivation. During the initial period, the hydrodechlorination rate decreases less quickly than the hydrogenation rate and this results in a fast increase of ethylene selectivity which reaches a maximum at the end of this period. After the initial period, the hydrodechlorination rate decreases faster than the hydrogenation rate and this results in a slow decrease of ethylene selectivity. A comparison between the physico-chemical properties of the fresh catalyst and of the deactivated one suggests a deactivation mechanism by poisoning or coking of silver sites at the surface of the active Pd-Ag alloy particles whereas palladium sites would remain intact. The selectivity evolution during the second period, that is, after the very first operating hours, is in agreement with such a mechanism. However, the sharp ethylene selectivity increase during the initial operating hours suggests, in addition to the deactivation by silver sites disappearance, the presence of a further nonidentified phenomenon. The characterization of the catalyst after a regeneration treatment including an oxidation step followed by a reduction step shows that this treatment allows restoration near to the physico-chemical properties of the fresh catalyst. (C) 2003 Elsevier Inc. All rights reserved. [less ▲]

Time-resolved SAXS measurements of phase separations during silica gel formation

Poster (2003, October)

Synthèse et caractérisation de catalyseurs métalliques supportés sur carbone de texture contrôlée par procédé sol-gel

Conference (2003, September 15)

Non destructive measurement of shrinkage, cracks and moisture profiles by X-ray microtomography : application to wastewater sludge convective drying

Scientific conference (2003, September)

Use of X-ray microtomography to determine internal moisture profiles during convective drying of deformable materials

in Saravacos, G.; Maroulis, Z. B.; Krokida, M. (Eds.) et al Proceedings of the European Drying Symposium - EuDrying03 (2003, September)

Preparation of macroporous biodegradable poly(L-lactide-co-epsilon-caprolactone) foams and characterization by mercury intrusion porosimetry, image analysis, and impedancy spectroscopy

in Journal of Biomedical Materials Research (2003), 66A(2), 199-213

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying ... [more ▼]

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying solutions in dimethylcarbonate. Most of the freeze-dried foams, prepared by varying polymer concentration and cooling rate, exhibited two main pore populations: (1) longitudinally oriented tube-like macropores with diameters greater than or equal to100 mum, and (2) interconnected micropores (10-100 mum). Pore characteristics, including macropore density, mean diameter, and interdistance, as well as micropore density, area, and shape, were determined by image analysis of scanning electron micrographs in order to study the influence of processing and formulation parameters on foam structure and properties. The pore orientation and the 3-D texture also were studied by image analysis and impedance spectroscopy. In the case of the P(LA-co-CL5), the macropore diameter increased with the cooling rate while the micropore diameter decreased. The micropores also became more circular when the cooling rate was increased. The pore size and morphology of the P(LA-co-CL40) were quite unchanged by varying the cooling rate. All the other conditions being the same, the P(LA-co-CL5) foams were better organized than the P(LA-co-CL40) foams, and pore orientation was improved at the higher cooling rate. Pore size and morphology also can be controlled by changing the polymer concentration (Cp), as we showed by studying P(LA-co-CL5) foams prepared by freeze-drying solutions in the 1-10 w/v% Cp range. Macropore density, average diameter, and interdistance of P(LA-co-CL5) foams increased with Cp, but the micropore characteristics remained almost unchanged no matter the Cp. The reliability of the characterization methods has been discussed, with special attention to mercury intrusion porosimetry, which is used primarily for measurement of pore volume and pore size distribution. However, this technique is reported here as a destructive and unreliable method for the characterization of fragile P(LA-co-CL40) foams. This study shows that image analysis and impedance spectroscopy can give reliable information relative to the pore morphology and anisotropy of freeze-dried foams. [less ▲]