Hydrothermal Stability of Mesoporous SBA-15 Modified with Alumina and Titania

Abstract

Hydrothermal stability of alumina or titania modified SBA-15 was studied. Al2O3 and TiO2 were introduced into the SBA-15 structures either by post-synthetic deposition or isomorphous substitution. Appropriate isopropoxides were applied as the reagents for modifications.  In all cases surface area and pore volume on non-modified SBA-15 decreased significantly after hydrothermal treatment. Surface  decreased by more than 60% after 2 hs at 975 K. Stabilization effect was found only after introduction of titanium and aluminum ions via sol-gel technique. Here, the decrease of surface area was only 20% of the initial one. Independently from the stabilization effect of  the SBA-15 structure the creation of surface acidity was also possible. In contrast, the stabilization effect after isomorphous substitution was negligible. All samples were studied with XRD, TEM, nitrogen sorption at 77 K, TPD of ammonia. Hydrothermal stability was tested under water vapour at temperatures up to 975 K.