Silica-alumina catalyst with bimodal pore structure prepared by phase separation in sol-gel process

An amorphous silica-alumina catalyst with distinct bimodal pore structure w as prepared by sol-gel reactions of tetraethoxysilane (TEOS) and aluminum n itrate in the presence of poly(ethylene oxide) (PEO). It contains macropore s effective for rapid molecular transportation and mesopores providing a la rge specific surface area of similar to 600 m(2) g(-1). The pore size distr ibution of the macropores is sharp and its average diameter varies from 0.3 to 5 mum by altering the starting compositions such as water/TEOS and PEO/ TEOS weight ratios. The macropores are formed when transitional morphologie s of spinodal decomposition are fixed by sol-gel transition of inorganic co mponents, and their size is controlled by altering the timing of the onset of spinodal decomposition and gelation. A change in the starting compositio n would affect this timing. In addition to macropores, silica-alumina has a large number of Bronsted acid sites, and shows excellent catalytic activit y in the cracking of cumene. PEO would have the effect of increasing the un iformity of Al atoms in the silica network, which would be a cause of the f ormation of Bronsted acid sites. (C) 2001 Academic Press.