Sulfonic acid-functionalized mesoporous silicas: Microcalorimetric characterization and catalytic performance toward biodiesel synthesis

In this work the synthesis of two sulfonic acid-functionalized mesoporous silica-based materials (SBA-15-propyl-SO3H and SBA-15-phenyl-SO 3H) through a co-condensation method is reported. The samples were characterized by means of SAXS, N2-adsorption/desorption isotherms, FTIR spectroscopy and thermogravimetric analysis. In addition, the surface acidity of the samples was investigated through ammonia adsorption microcalorimetry. We found that both the number and the strength of acid sites of SBA-15-phenyl-SO3H catalyst are higher than those of SBA-15-propyl-SO3H. The total number of acid sites was 808 μmol/g and 122 μmol/g for SBA-15-phenyl-SO3H and SBA-15-propyl-SO 3H, respectively. The two materials were then used as acid heterogeneous catalysts for the interesterification of extra virgin olive oil with ethyl acetate to produce biodiesel. We found a higher catalytic activity of SBA-15-phenyl-SO3H respect to SBA-15-propyl-SO3H in agreement with the microcalorimetric acidity measurements. Phenyl-sulfonic acid-functionalized SBA-15 seems to be a promising acid heterogenous catalyst for the preparation of biodiesel through the interesterification of triglycerides with ethyl acetate.