Xerogels chemical stability

The chemical stability of the Si—O—Si network is high under acidic conditions but is very low when in contact with a basic solution3. Therefore, treatment of the xerogel of 40 with aqueous sodium hydroxide leads to a complete dissolution and to the formation of the bis-trisilanolate 80 (equation 21)168. 

We attempted to improve the eatalytic performanee, including stability, of the silica-immobilized Co-POM catalysts by using hydrothermally stable supports, specifically, the mesostructured silicates SBA-15 and MCF, both modified with amino groups by grafting 3-aminopropyltrietoxysilane [97], The physico-chemical properties of three representative NH2-X (X = xerogel, SBA-15 and MSF) supported Co-POM catalysts are given in Table 1. The textural properties of the initial, POM-free supports are shown for comparison. 

The nature and structure of the surface of the xerogel are important characteristics with consequences which determine its chemical reactivity and stability. 

One example of a catalyst anchoring onto the hybrid xerogel s framework is the chemical modification of a dendrimer xerogel126. In the starting dendrimer xerogel, the high specific surface area (> 1000 m2 g-1) is combined with a good hydrothermal stability (up... 

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