Preparation of microporous acidic oxides from aluminum-bridged silsesquioxanes and catalytic activities for the cracking of hydrocarbons

The catalytic activities of a series of porous oxides prepared from silsesquioxanes for the cracking of hydrocarbons have been examined. In addition to known group 13 element-containing silsesquioxanes, new aluminum-bridged silsesquioxanes bearing various countercations, [Y]+[{(c-C5H9)7Si7O12(SiMe3)}2Al]− ([Y]+ = [H2NMe2]+ (2b), [HNMe2(C8H17)]+ (2c), [HNMe2(C18H37)]+ (2e), [HNC5H5]+[{(c-C5H9)8Si8O13}2Al]− (3d), and [HNC5H5]+[{(i-C4H9)8Si8O13}2Al]− (4d), have been synthesized. The controlled calcination of these silsesquioxanes at around 823 K produced amorphous porous acidic oxides with high BET surface areas of 360–520 m2 g−1 and uniformly controlled micropores of 5–6 Å diameter. Among the oxides examined, those prepared from aluminum-bridged silsesquioxanes show excellent catalytic activities for the cracking of cumene even at low reaction temperatures of around 523 K. Under identical conditions commercially available silica–alumina catalysts do not show significant activities, indicating exceptionally high activities of the silsesquioxane-based oxides despite their amorphous nature.