Synthesis and characterization of GaSBA-15: Effects of synthesis parameters and hydrothermal stability

Abstract

A series of highly ordered mesoporous GaSBA-15 materials have been synthesized using different Ga sources with Pluronic P123 by simply adjusting the molar ratio of water to hydrochloric acid (nH2 O / nHCl) under direct hydrothermal conditions. To control the structural and textural properties with high gallium incorporation in the framework of SBA-15, the GaSBA-15 has been prepared using different crystallization temperature. The synthesised GaSBA-15 materials have been characterized by ICP-AES, XRD, N2 adsorption, 71Ga MAS NMR, and FE-SEM. Gallium(III) nitrate is found to be a good Ga-ion source for the synthesis of mesoporous GaSBA-15 material, with nSi/nGa ratio up to 11.2 successfully prepared by changing the nSi/nGa ratio in the synthesis gel at nH2 O / nHCl of 295. By increasing the crystallization temperature from 373 to 403 K, nitrogen adsorption measurement shows that the pore diameter of GaSBA-15 can be tuned from 88.4 to 92.7 Å, with an increase of pore volume from 1.08 to 1.17 cm3/g accompanied by the concomitant decrease of surface area from 981 to 783 m2/g and the decrease of pore wall thickness from 35.3 to 32.7 Å. 71Ga MAS NMR results demonstrate that a large amount of tetrahedral gallium could be incorporated into the framework of SBA-15. Furthermore, the hydrothermal stability of GaSBA-15 samples has also been investigated, with hexagonal GaSBA-15(5) having better hydrothermal stability than GaSBA-15(50). © 2008 Elsevier Inc. All rights reserved.