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

摘要

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)(7)Si7O12(SiMe3)}(2)Al](-) ([Y](+) = [H2NMe2](+) (2b), [HNMe2(C8H17)](+) (2c), [HNMe2(C18H37)](+) (2e), [HNC5H5](+)[{(c-C5H9)(8)Si8O13}(2)Al](-) (3d), and [HNC5H5](+)[{(i-C4H9)(8)Si8O13}(2)Al](-) (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 m(2) g(-1) and uniformly controlled micropores of 5-6 Angstrom 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. (C) 2004 Elsevier Inc. All rights reserved.