Aerogel Catalysts

Abstract

Aerogels are often largely mesoporous solids, with a porosity which may exceed 90 vol% and a specific surface area up to 1000 m2 g-1. Such materials were first obtained by Kistler in 1932, and designate gels in which the liquid was replaced with a gas without collapsing the gel solid network. Contrary to xerogels dried from wet gels by evaporation with an important shrinkage, the first aerogels were obtained by a “supercritical drying” technique in which the liquid which impregnated the gels was evacuated after being transformed to a supercritical fluid. The diversity in nature of the solid constituting the rigid network is very large. It includes simple oxides, multi oxide compositions, organic and hybrid organic-inorganic polymers and carbon. This diversity as well as the high specific pore volume and surface area make aerogels applicable either as catalysts or as catalyst supports. Besides, molecular catalysts such as transition metal complexes or enzymes can easily be immobilized in aerogels, which opened the road to new supported molecular catalysts and biocatalysts. This communication reviews the synthesis and properties of oxide aerogel catalysts.