Vacuum Calcination Behavior of SBA-15 Ordered Mesoporous Silica

In this paper, the calcination of SBA-15 in vacuum is followed by in situ and ex situ small angle X-ray scattering (SAXS) measurements at different temperatures and the material properties are compared with the conventional calcination process in nitrogen and air. The whole process of template decomposition and by-products elimination is investigated as a function of temperature, showing early stages of polymer decomposition at 200 °C. The textural properties of the vacuum-calcined material, analyzed by nitrogen adsorption isotherm data at the end of the calcination process at 540 °C, revealed a smaller surface area and no detectable volume of micropores. A sharp monomodal pore size distribution with a mean value around 108 Å is obtained, larger than the material calcined via the usual procedure, which gives values around 98 Å. The results indicate that the vacuum heat treatment is an alternative calcination strategy for applications which require a well-ordered mesoporous structure, rigid pore walls, and large pore diameters.