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-contai ning micelle-templated silica (Al-MTS) with Si/Al atomic ratios in the rang e 8-45. The synthesis proceeds at ambient temperature, atmospheric pressure , acid medium and for only 3 h. For the calcined materials, a decrease of b oth the d(100) spacing and the pore size, as well as an increase in the wal l thickness, are observed with increasing aluminum content. Thus, the avera ge pore size changed from 2.4 nm (Si/Al=45) to 1.4 nm (Si/Al=8), i.e. the p ore size reaches the micropore range without varying the chain length of th e surfactant used as micellar templating agent. The Al-27 NMR-MAS spectra s how that in the as-synthesized samples the aluminum is present as tetrahedr ally coordinated species, which are partially transformed into octahedral a luminum upon calcination. Since the synthesis takes place in the absence of alkali cations, the Al-MTS materials are directly obtained in the acid for m, making a subsequent ion exchange and calcination treatments superfluous. (C) 2000 Elsevier Science B.V. All rights reserved.