Eric Prouzet

Nanometric hollow spheres made of MSU-X-type mesoporous silica

Submicrometric hollow spheres with mesoporous walls were prepared by applying the synthesis of MSU-X type mesoporous silica at neutral pH. The application of ultrasound in the proper power range, to a mixture of nonionic polyoxyethylene surfactant and unreacted silicon alkoxide (tetraethylorthosilicate) gives a stable emulsion where the cavitation bubbles created by the ultrasound are trapped in the solution. Further hydrolysis and condensation of the silica by the addition of sodium fluoride freezes the structure and gives a powder that exhibits a single reflection in the X-ray diffraction pattern, characteristic of a 3D-wormhole ordered porous framework. Its main feature is a large hysteresis loop in the nitrogen adsorption/desorption isotherm. This hysteresis loop corresponds to the retention of condensed nitrogen within the voids of these particles that can play the role of tanks for volatile compounds.

EXAFS identification of the active species in supported niobium sulfide hydrotreatment catalysts

Abstract We present a Nb K-edge EXAFS study of carbon- and alumina-supported niobium sulfide hydrotreatment catalysts. NbS 2 and NbS 3 entities have been evidenced on the carbon support, and NbS 2 and Nb 1− y S ones on the alumina support. EXAFS spectra of carbon-supported species, which are highly disordered, were analyzed through an asymmetric distance distribution model. Considering their poor dispersion, Nb 1− y S species can be thought to be intrinsically highly active. Their activity, and that of NbS 3 entities as well, can possibly be related to cation clustering. Niobium sulfides appear as very sensitive to support effects.

Electrochemical intercalation of lithium into vanadium pentaoxide: an in situ X-ray absorption study

An X-ray absorption study at the vanadium K edge has been performed on the LixV2O5(x= 0–0.78) system. For this, an electrochemical cell has been designed in order to allow in situ measurements. The spectra were recorded every 0.03 Li (mol V2O5)–1 using the same sample left in the X-ray beam. The study of the XANES spectra shows that the vanadium environment becomes more symmetrical as the intercalation progresses. Furthermore, the Natoli rule applied to these spectra reveals a mean lengthening of the vanadium–oxygen bond of 0.05 A. This result is confirmed by the EXAFS study. This EXAFS study also reveals a shortening of the vanadium–vanadium bond of 0.08 A. The results are interpreted as being due to the partial reduction of vanadium(V) to vanadium(IV), and its move from its initial position in a square pyramid towards the basal oxygen plane of the pyramid.

Performances of ceramic filters for air purification

Abstract In this work, we shall expose the main results obtained with ceramic air filters (CAF) having different characteristics. CAF are discs in which the filtration area is equal to 130 cm 2 . The influence of face velocities of the aerosols varying from 0.5 to 14 cm/s, of porous volume, ranging from 48 to 58%, of pore diameters ranging from 11 to 14.8 μm and of thickness of the filters (from 1 to 3.2 mm) on the values of the penetration and the pressure drop will be pointed out. Particle penetration which depends on the values of these parameters have been measured in the range from 10 −6 to 5×10 −2 which corresponds to an efficiency varying from 99.999999 to 99.95%. Relative performances of filters have been analyzed in terms of figure of merit.

An ultrafiltration membrane, prepared with MSU-type mesoporous silica: Preparation and specific filtration behavior

We report preparation and the singular filtration properties of an ultrafiltration membrane made with MSU-type mesoporous silica that exhibits cylindrical pores aligned mostly normal to the support. This membrane supported on tubular commercial macroporous alumina supports was prepared by the interfacial growth mechanism between stable silica-surfactant hybrid micelles made of the association of silica oligomers with polyethyleneoxide-based (PEO) surfactants and sodium fluoride, a well-known silica condensation catalyst. It appears that the combined effect of the silica nature of the membrane, whose surface charge can be easily adjusted by changing the pH and the non-connected cylindrical shape of the pores provides a new behavior in the retention properties, as proved by the filtration of polyoxyethylene polymers (PEO) with different molecular weights. Depending on the filtration conditions a rejection rate of 80% and a steep cut-off at 2,000 Da can be obtained or, on the reverse, polymers three times bigger than the pore diameter can diffuse through the membrane. This new filtration mechanism, which opens up new modes of separation modes, is explained in the light of both topology of the porous network and pH-dependent interactions between PEO polymers and silica porous media.

Turning Commercial Ceramic Membranes into a First Stage ofMembranes for Post-Combustion CO2 Separation

This report describes how commercial tubular ceramic membranes, initially designed for liquid filtration, can be modified to provide the core separation components of a first stage of flue gas treatment and enrichment in post-combustion CO2 separation. Commercially available tubular NanoFiltration (NF) ceramic membranes were turned into a membrane for CO2 separation by a two-step process including additional ceramic coating and chemical grafting. The combination of ceramic coating and chemical grafting drastically modify the membrane properties and turn the membrane initially designed for liquid filtration into a membrane that displays CO2 vs N2 selectivity at the opposite of Knudsen-based selectivity, with a CO2:N2 ideal selectivity of 2.3. A second step of this study addressed the reduction of membrane cost, by starting with a low ultrafiltration (UF) 200 nm ceramic support specifically manufactured for this application in place of a NF membrane. After successful coating of a 5 nm and a 1 nm ceramic membranes, this membrane, grafted with a commercial fluorosilane molecule was tested in pure gas permeation of CO2 and N2, with an ideal selectivity CO2:N2=3. Finally, the same membrane, grafted with glymo, was tested against separation of a CO2 (20%):N2 (80%) mixture, and as a function of the permeation stage-cut. A CO2:N2 selectivity of 4 was obtained for a stage-cut of 0.5, and even higher (CO2:N2 selectivity=14) for low stage-cuts usually used for testing dense polymer membranes. These results demonstrate that commercial ceramic porous membranes can be used as starting elements for a first stage of CO2 post-combustion gas cleaning and CO2 enrichment.