About the thermal stability and pore elimination in the ordered hexagonal mesoporous silica SBA-15

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ordered hexagonal mesoporous silica was prepared using Pluronic P123 template and removal of the polymer by washing in ethanol. The thermal stability and the pore elimination was studied under heat treatment by a fixed time at 500, 600, 750, 825, 900, and 1050 degrees C. The most part of the porosity is built up by cylindrical pores belonging to the ordered hexagonal 2D pore structure. The lattice parameter and the pore volume of the hexagonal 20 structure diminish regularly with the temperature up to 900 degrees C. All porosity is eliminated at 1050 degrees C. The porosity elimination occurs in a mechanism described by a geometric model of contracting area, in which the diameter of the cylindrical pore diminishes while its length is kept constant. An activation energy of (92 +/- 2) kJ/mol was estimated for the process. The ordered porosity of an ethanol-washed and vacuum dried sample was found to be even larger with a narrower pore size distribution in comparison to a sample directly calcined at 500 degrees C without previous washing in ethanol. (C) 2014 Elsevier Inc. All rights reserved.