A sol-gel approach for the room temperature synthesis of Al-containing micelle-templated silica

A two-step sol-gel method has been developed for the synthesis of Al-containing micelle-templated silica (Al-MTS) with Si/Al atomic ratios in the range 8-45. The synthesis proceeds at ambient temperature, atmospheric pressure, acid medium and for only 3 h. For the calcined materials, a decrease of both the d(100) spacing and the pore size, as well as an increase in the wall thickness, are observed with increasing aluminum content. Thus, the average pore size changed from 2.4 nm (Si/Al=45) to 1.4 nm (Si/Al=8), i.e. the pore size reaches the micropore range without varying the chain length of the surfactant used as micellar templating agent. The Al-27 NMR-MAS spectra show that in the as-synthesized samples the aluminum is present as tetrahedrally coordinated species, which are partially transformed into octahedral aluminum upon calcination. Since the synthesis takes place in the absence of alkali cations, the Al-MTS materials are directly obtained in the acid form, making a subsequent ion exchange and calcination treatments superfluous. (C) 2000 Elsevier Science B.V. All rights reserved.