A Review on the Silica Aerogels-Supported Catalysts

Silica aerogels are attractive candidates as catalyst support due to their very large surface area and high open porosity. This paper reviews the silica aerogel supported catalysts. General methods of silica aerogel synthesis and catalytic phase incorporation into aerogel matrix described. Aerogel synthesis consists of two main steps: wet gel preparation and drying the gel to obtain aerogel. Catalytic active phase can be added before or after silica gel formation. In the first approach, active phase precursor or as-prepared nanoparticles added to silica precursor. Active phase introduced into matrix structure during the gelation of matrix. In the second approach, active phase either impregnated on the silica wet gel or deposited on the aerogel by impregnation or vapor infiltration. Aerogel catalysts synthesis and aerogel drying methods, and used silica precursor as well as the studied reactions in the catalytic application of silica aerogel have been collected. Finally, a comparison between the properties and performance of the aerogel and xerogel catalyst have been presented which results confirm the favorable properties and better performance of aerogel catalysts in comparison with xerogel catalysts. As typical results in different studies, for aerogel catalyst the specific surface area up to 3.9 times larger, the pore volume up to 23 times larger, the reactant conversion up to 7.5 times larger, the product yield up to 7 times larger, and the desired product selectivity up to 4 times larger than those for xerogel catalyst have been obtained.