Francis Noville

Study of the texture of monodisperse silica sphere samples in the nanometer size range

Abstract The texture of monodisperse silica spheres in the diameter range 8–200 nm, and in the form of powders and slabs is examined. The analysis of nitrogen adsorption—desorption isotherms shows the respective contributions of the voids between particles and the internal microporosity, as well as the influence of pelletization on texture. The importance of the adsorbent—adsorbate interactions on the selection of the standard isotherms to obtain a self-consistent picture of the solid texture is also emphasized.

Texture of manganese nodules used as a catalyst for demetallizing and desulphurizing petroleum residua

Abstract The porous texture of oceanic polymetallic nodules used as catalysts for demetallation and desulphurization of petroleum residua in a trickle bed reactor was studied after reaction. Four techniques were considered: analysis of nitrogen physical adsorption—desorption isotherms, X-ray diffractometry, mercury penetration and electronic microscopy. The nodules present a remarkable specific surface area and porosity, which are partially conserved at high temperatures even under the drastic conditions of hydrotreatment.

Texture and sintering of zirconium dioxide-yttrium oxide ceramics

Abstract Mercury porosimetry was used to investigate the behaviour of two commercial yttriastabilized zirconias during sintering. It was found to be advantageous to use as the initial powder a material characterized by a monodisperse distribution of small particle sizes in order to lower the temperature of total densification.

Hydrodemetallation of petroleum atmospheric residua using oceanic manganese nodules in a trickle bed reactor

Abstract Oceanic polymetallic nodules could be used as a catalyst and adsorbent for hydrodemetallation and hydrodesulfurization of petroleum residua in a trickle bed reactor because of their particular composition and porous texture. A kinetic study of these reactions has been undertaken in a micro-pilot unit using operating conditions similar to those encountered in industrial reactors. The effect of the main operating parameters (pressure, temperature, mass flow rates) was investigated. Moreover, the evolution of the porous texture during reaction was examined and the performance of an industrial reactor estimated.

Is it possible to obtain a coherent image of the texture of a porous material

This study consists in verifying the coherence of a few commonly used analysis methods of nitrogen adsorption-desorption isotherms. These methods were tested on model samples obtained by mechanically mixing two micro- and mesoporous solids respectively with known mass proportions. Although the individual analysis methods may lead to discrepancies in the interpretation of the isotherms, their systematic comparison allows drawing a coherent picture of the porous texture.

Qualitative assessment of the purity of multi-walled carbon nanotube samples using krypton adsorption

Abstract Krypton is a subcritical vapour at the nitrogen boiling temperature. As such, its adsorption on crystalline surfaces leads to condensation steps, typical of type VI isotherms according to IUPAC, while its adsorption on rough surfaces is BET-like. Based on this property of krypton adsorption at 77 K, a methodology is proposed to determine the purity of carbon nanotubes samples. The method is tested on model samples obtained by mixing mechanically purified multi-walled carbon nanotubes with various amounts of the same catalyst as used for their synthesis.

Deactivation mechanisms and regeneration of a bimetallic hydrodechlorination catalyst

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO 2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. 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 Ag sites at the surface of the active Pd−Ag particles. A regeneration treatment is proposed which allows to restore the initial properties of the fresh catalyst.

Silica-zirconia monoliths from gels

Zirconium propoxide and tetraethylorthosilicate were hydrolyzed in methoxyethanol which acts as stabilizer of zirconium and in presence of formamide or dimethylformamide as Drying Control Chemical Additives in order to obtain zirconia silica gels. The gels were dried at 70°C to get monolithic xerogels. The influence of zirconium content and DCCA on texture was determined. The evolution of these xerogels was investigated as a function of temperature between 70°C and 1000°C by thermogravimetry, differential scanning calorimetry, I.R. spectroscopy and R.X. diffractometry.

Texture evolution of zirconium oxide xerogels prepared by sol-gel process

Abstract Zirconium propoxide was hydrolyzed in methoxyethanol in order to obtain zirconia gels. The gels were dried at 110°C to get xerogels. The textural and crystalline evolution of these xerogels was investigated as a function of temperature between 110 and 800°C. The influence of hydrolysis ratio of the zirconium propoxide, as well as the effect of stabilizers such as calcium, magnesium and yttrium cations, were studied in order to define the most suitable experimental conditions to obtain dense bulk zirconia ceramics.

Preparation and characterization of porous BaTiO3 xerogels by sol-gel process

Abstract Homogeneous BaTiO3 gels are prepared by hydrolysis and polycondensation between titanium isopropoxide and barium hydroxide in the presence of methoxyethanol, methanol and water. Two drying methods are used: the first one under vacuum and the second one under a nitrogen flow. The influence of the drying method on the texture is studied through nitrogen adsorption-desorption isotherms analysis. A heat treatment is defined on the basis of the thermogravimetry (TG) and differential scanning calorimetry (DSC) results. The influence of the calcination temperature on the texture and the crystallization of the solids is discussed.