ABSTRACT
Depending on the impregnation conditions, the metals can be found deposited as nanoclusters on the surface of the mesoporous structure or included within the silica hexagonal pores. Mesoporous silica has been widely used as the base material to develop chemical gas sensors. There are mainly three different kinds of mesoporous molecular sieves used in catalysis. The first one is the so-called M41S family of silica and aluminosilicates. The second one is the hexagonal mesoporous silica HMS and MSU families. The hexagonal SBA-15 materials exemplify the third family. Palladium forms small nanoclusters on the surface of the mesoporous structure whereas Platinum (Pt) impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores. Golden is preferentially placed forming big clusters outside the mesoporous structure, leading to a small catalytically active surface area and thus exhibiting a small catalytic effect.
