Sulphonated mesoporous silica-carbon composites and their use as solid acid catalysts

The synthesis of highly functionalized porous silica-carbon composites made up of sulphonic groups attached to a carbon layer coating the pores of three types of mesostructured silica (i.e. SBA-15, KIT-6 and mesocellular silica) is presented. The synthesis procedure involves the following steps: a) removal of the surfactant, b) impregnation of the silica pores with a carbon precursor, c) carbonization and d) sulphonation. The resulting silica-carbon composites contain ~ 30 wt % of carbonaceous matter with a high density of acidic groups attached to the deposited carbon (i.e. -SO3H, -COOH and -OH). The structural characteristics of the parent silica are retained in the composite materials, which exhibit a high surface area, a large pore volume and a well-ordered porosity made up uniform mesopores. The high density of the sulphonic groups in combination with the mesoporous structure of the composites ensure that a large number of active sites are easily accessible to reactants. These sulphonated silica-carbon composites behave as eco-friendly, active, selective, water tolerant and recyclable solid acids. In this study we demonstrate the usefulness of these composites as solid acid catalysts for the esterification of maleic anhydride, succinic acid and oleic acid with ethanol. These composites exhibit a superior intrinsic catalytic activity to other commercial solid acids such as Amberlyst-15.