Preparation of SiO2 and SiO2–Al2O3 catalysts by gel skeletal reinforcement using hexamethyldisiloxane (HMDS) and acetic anhydride and aluminum tri-sec-butoxide (ASB) systems and elucidation of their catalytic cracking properties as matrices

Abstract

Novel amorphous silica with extremely large mesopores were prepared using the gel skeletal reinforcement method with hexamethyldisiloxane (HMDS) and acetic anhydride (AA) system as reinforcing reagents. Pore volume and pore diameter increased with increasing the amounts of HMDS added. When three times higher moles of HMDS than that of silica source TEOS were used, pore volume and pore diameter of prepared amorphous silicas reached larger than 5 cm3/g and 44 nm, respectively, even after calcination at 600 °C for 3 h. The mixed catalysts prepared with the reinforced silica, β zeolite and alumina-sol binder showed much higher conversions of n-dodecane than respective single zeolite even though these catalysts included only 26 wt% of zeolite. The activity tended to increase with increasing pore size and pore volume of the reinforced silica. When aluminum tri-sec-butoxide (ASB) was used as a gel reinforcing reagent, alumina was introduced on the silica surface. In catalytic cracking of n-dodecane the mixed catalysts using ASB reinforced silica showed higher conversion than the catalysts using HMDS, indicating that silicas reinforced by ASB formed silica–alumina in the external surface which played a role of additional acid sites.