Silica–alumina catalysts prepared in sol–gel process of TEOS with organic additives

Abstract

Amorphous silica–alumina catalysts were prepared in the sol–gel reaction of tetraethoxysilane in the presence of aluminium nitrate and various organic additives, and the effects of the additives on both pore formation and acid-site generation were investigated. Macropores with bicontinuous morphology are formed in the system with poly(ethylene oxide) (PEO) with an average molecular weight of 10 0000, when a transitional structure of spinodal decomposition is fixed by sol–gel transition of inorganic components. In the systems with other organic additives with low molecular weight, such as ethylene glycol oligomers and citric acid, silica–alumina is provided with only mesopores. Although their mesopore structures are not affected by organic additives, the catalytic activity varies depending on the kind of organic additives. It is found that organic additives with the ability to increase the interaction between silica oligomers and aluminium cations increase the dispersion of Al in the silica network, resulting in high catalytic activity in the cracking of cumene. PEO interacts with both silica and aluminium cations in the sol–gel solution, so that macroporous silica–alumina prepared in the presence of PEO shows excellent catalytic activity.