Synthesis of sulfonic SBA-15 by co-condensation and soxhlet extraction: optimization by shortening the preparation time

Abstract

Propyl sulfonic SBA-15 catalysts are of great interest in several fields of chemistry and have exhibited high activity towards numerous reactions. Nonetheless, the incorporation of these functional groups on SBA-15 silica poses several challenges. Grafting techniques may conduct to a non-uniform dispersion of the functional groups on the surface. Co-condensation of the functional precursor during the synthesis of the silica overcomes this drawback, but requires longer syntheses and it has the disadvantage that removal of surfactant cannot be done by calcination because of the thermal stability of the functional groups present on the surface. Thus, the detemplation is limited in this case to extraction by standard procedures which generally involve large amounts of solvent per gram of catalyst, long contact time and limited yield of the template removal. The aims of this work were, on the one hand, to study the reduction of the ripening time for catalysts prepared by co-condensation with sulfonic groups and, on the other hand, to develop a standard procedure which allows achieving a high yield of detemplation and optimizes the amount of solvent needed and the time required, as well as employ a commercially available solvent. Different characterization techniques allowed to conclude that the obtained materials exhibited high surface area and a good degree of mesoscopic order, comparable with materials obtained by traditional procedures. Also, a high degree of template removal was achieved and the sulfonic groups were preserved in functionalized materials. These results are relevant for a further scale-up of the catalysts production.