Precipitated silica surface modification

In this section, only the surface modification techniques will be discussed, and not the impregnation, sol-gel or co-precipitation techniques. Furthermore, it is not our aim to fully cover all chemical modifications on the silica surface. We merely want to present in introduction to and an insight in the fast expanding field of silica modifications, in order to create new catalysts, sensors and immobilizators. 

Jesionowski, T.,Zurawska, J., Krysztafkiewicz, A., Pokora, M., Waszak, D., andTylus, W. 2003. Physicochemical and morphological properties of hydrated silicas precipitated following alkoxysilane surface modification. Appl. Suif. Sci. 205 212—224. 

The modification of the silica surface activity is obtained via silanization in situ, which has been used to reduce the silica polarity. As expected, it was observed a reduction in the G and in the Payne effect as the silanization takes place in the precipitated silica. Analyzing the dependency of G as function of deformation amplitude to the compound SBR-2/sUica/silane, it can be seen that the silanization leads to a decrease of 2.5 ties of the G value in comparison to the reference compotmd. However, it should be noticed that first, the reduction of the Payne effect is remarkably lower than that obtained to the SBR-2(ep7) and non sUanized silica compound and, second, the value of G obtained to SBR-2(ep7) and sUanized silica is comparable to the SBR-2/sifica/silano system. 

Precipitation of increasing amounts of alumina in the silica hydrogel leads to drastic modifications of the gel texture. Up to 10 wt% of alumina, silica-alumina texture is related to that of silica, although pore volume, pore radius and pore surface are more or less increased. 

In a former study, we have prepared very highly loaded nickel catalysts, efficient for the hydrogenation of edible oil, by a (DP) method and examined the influence of the carrier surface area on the metallic dispersion and on the metal interaction with the silica. The best activity in soybean oil hydrogenation was obtained using a macroporous support with an intermediate surface area, the FC Celite (Manville) (16). We also observed that precipitate aging, at the end of the (DP) method, induced important modifications in the textural properties of the catalysts. 

---