Benoit Koch

Influence of preparation methods on the texture and structure of titania supported on silica

Deposition of titanium over a silica support was performed by three methods: precipitation with TiCl4 and ammonium hydroxide in aqueous solution; impregnation with titanium(IV) isopropoxide in isopropyl alcohol; grafting with a solution of TiCl4 in hexane. Samples were characterized by BET, XPS, zeta potential, DBS, XRD, SEM and EPMA. The method of deposition influences deeply the morphology and dispersion of the coated oxide. With the precipitation method, TiO2 is deposited at the external surface of the silica. Impregnation provides the best external superficial dispersion of titania allowing the formation of small crystallites at its surface. The grafting method gives the best internal TiO2 dispersion with formation of large crystallites at the external surface of silica. A strong interaction is found between titanium and silicon. This work also draws attention to the many analytical techniques needed to characterize the TiO2-coated supports.

Preparation and characterization of catalytic supports with variable composition in the system SiO2-Al2O3-AlPO4

A single method to synthesize supports of any composition in the system SiO 2 -Al 2 O 3 -AlPO 4 is developped. Changing the chemical composition and controlling the preparation parameters allow to obtain supports with very different porosimetric and catalytic properties. The synthesis method has been designed to avoid phase segregation which generally givesmaterials which are poorly resistant to thermal recrystallization. Most supports are characterized by a high value of both the specific surface and the pore volume with a good thermal recrystallization stability. We analyzed the influence of the main experimental parameters on the properties of the supports.

Preparation of titania supported on silica via the vapor phase grafting method: application of statistical and physico-chemical methods

The parameters influencing the dispersion and the loading of titanium on silica support (support calcination temperature, grafting temperature and TiCl4 vapor pressure) were studied using two statistical methods. In the first method, a strategy for efficient design of experiments was used. In the second one, the significance of the parameters (or their interactions) was estimated by using a statistical model. A physico chemical characterization (chemical composition, X-ray diffraction, BET surface area, XPS and the OH- group concentration of the support) has been used to correlate the statistical results. From the analysis of the modeled responses (titanium content and dispersion) it can be concluded that an adequate control of the experimental conditions leads to titanium-silica support catalysts with a controlled amount of titanium but with different titanium dispersion. An attempt to correlate the degree of disperson with the type of reaction occurring on the surface of silica during the grafting is proposed.

Synthesis and characterization of catalyst supports with composition xSiO2-xAlPO4-(100-2x)TiO2

Abstract Several xSiO 2 –xAlPO 4 –(100–2x)TiO 2 catalyst supports were investigated with regard to their structural and textural properties. Their textural properties were found to depend on their chemical composition. Low titania content (5 mol%) led to an increase of the BET surface area, whereas a higher titania content virtually did not modify the BET specific surface area, but did lead to a decrease of the pore volume. X-ray diffraction (XRD) and infrared (IR) data are in accordance with a good dispersion of titanium (up to 15 mol%) in the matrix. X-ray diffraction showed that the silica–aluminum phosphate matrix was present as an amorphous phase in all catalysts calcined at 973 K, but crystalline domains of anatase were found in supports containing 20 mol% or more titania.