Study of the structure of P- and Si-doped TiO2 xerogels in relation with their formation mechanism

Poster (2009, January)

Synthesis of Ag/TiO2 hybrid photocatalysts by sol-gel process with new P-alkoxide functionalized ligands

Poster (2009)

Study of the structure of P-doped TiO2 xerogels in relation with their formation mechanism

Poster (2009)

Multigram scale synthesis and characterization of low-density silica xerogels

in Journal of Non-Crystalline Solids (2006), 352(26-27), 2763-2771

The synthesis of silica with preserved porosity and tailored morphology by sol-gel process can be achieved by hybrid organic-inorganic synthesis: a modified alkoxide, viz. 3-(2-aminoethylamino ... [more ▼]

The synthesis of silica with preserved porosity and tailored morphology by sol-gel process can be achieved by hybrid organic-inorganic synthesis: a modified alkoxide, viz. 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), is introduced during the base catalysed synthesis with TEOS as main silica precursor. Additives with methoxy groups induce a nucleation mechanism because of their higher reactivity compared to main reagents with ethoxy groups. The nucleation model presented in previous papers was refined by taking into account the porosity of the particles and calculating the number of additive molecules by nucleus for each value of the ratio of additive/main reagent. The extrapolation of the synthesis process to semi-industrial scale goes through the replacement of laboratory grade reagents by industrial grade reagents and the scaling up to the production of higher quantities. At each of these two steps, the morphology and porosity of the samples has been compared to those of laboratory grade samples. It was shown that the texture and particle size has quasi totally been preserved. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Large-scale synthesis and shaping of xerogel catalysts

Poster (2006)

Non intrusive mercury porosimetry: Pyrolysis of resorcinol-formaldehyde xerogels

in Particle & Particle Systems Characterization (2006), 23(1), 72-81

When submitted to mercury porosimetry, some materials are penetrated by mercury whereas others, among the most porous, are densified by the isostatic pressure. Notably, this is the case for materials ... [more ▼]

When submitted to mercury porosimetry, some materials are penetrated by mercury whereas others, among the most porous, are densified by the isostatic pressure. Notably, this is the case for materials whose structure is made of particles aggregated into filament-like clusters that are interconnected in a 3-D array. Indeed, that kind of material undergoes a volume variation due to hierarchical pore collapse. In the case of intrusion, the mercury porosimetry data are classically analyzed by the Washburn equation. In the case of hierarchical pore collapse, data can be correctly analyzed by the collapse model equation. Using an equation that does not correspond to the mechanism leads to large errors in the pore size distribution. Thus, an accurate data analysis requires prior determination of the mechanism leading to the volume variation recorded as a function of the pressure. The present work particularly examines the complex and unusual behavior of partially pyrolyzed resorcinol-formaldehyde gels when submitted to mercury porosimetry. The unusual behavior encountered complicates the mechanism identification and, therefore, the equation selection. However, the major part of the volume distribution as a function of the pore size can be determined with a good accuracy. [less ▲]

Preparation and characterization of xerogel catalyst microspheres

in Journal of Non-Crystalline Solids (2004), 350

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead ... [more ▼]

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead production process, the xerogel catalyst was ground in water and mixed with ethylene glycol and sodium alginate, the latter of which is the gelation agent. The beads were formed at a vibrating nozzle and solidified during their fall in a water tank containing calcium ions, which induce cross-linking of the alginate and consequent bead hardening. Preliminary work was done using a syringe instead of the material-consuming BRACE unit. The beads were made from a suspension of dried only, dried and calcined, or dried, calcined, and reduced catalyst. The textural properties of the beads were analyzed by nitrogen adsorption-desorption isotherms and mercury porosimetry; and bead catalytic activity was tested for selective hydrodechlorination of 1,2-dichloroethane. The beads made from a suspension of dried catalyst appear to have properties the closest to that of the xerogel reference catalyst. Porosity and surface area are maintained at their level before bead formation. However conversion of 1,2-dichloroethane decreases after the production process, possibly due to poisoning by calcium ions. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

In situ SAXS analysis of silica gel formation with an additive

in Journal of Physical Chemistry B (2004), 108(26), 8983-8991

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino ... [more ▼]

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) as an additive are reported. The measurements reveal no discontinuity of the nanostructure at the gel point. A chemically induced spinodal phase separation is found to give a coherent picture of the collected data. Increasing the amount of EDAS induces the phase separation on a smaller length scale, which finally leads to a modified gel morphology. The SAXS measurements and the electron micrographs associated with the dry gels could be interpreted in terms of the suggested wet gel formation mechanism. [less ▲]

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. II. Viscosity study of the sol-gel transition

in Journal of Non-Crystalline Solids (2003), 320(1-3), 31-39

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed ... [more ▼]

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed by theological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive. the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Nucleation phenomenon in silica xerogels and Pd/SiO2, Ag/SiO2, Cu/SiO2 cogelled catalysts

in Journal of Sol-Gel Science and Technology (2003), 26(1-3), 827-830

Pd/SiO2, Ag/SiO2 and Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino) propyltrimethoxysilane (EDAS). It ... [more ▼]

Pd/SiO2, Ag/SiO2 and Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino) propyltrimethoxysilane (EDAS). It appears that, in cogelled samples, the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica porous particles with a monodisperse microporous distribution. Xerogels without metal synthesized with EDAS and TEOS (C. Alie, R. Pirard, A. J. Lecloux, and J.-P. Pirard, J. Non-Cryst. Solids 289, 88 (2001)) verify this hypothesis of nucleation by EDAS. [less ▲]