Synthesis, characterization and catalytic activity of MCM-41-type mesoporous silicas functionalized with sulfonic acid Original Research Article

This paper reports the results obtained in the synthesis, characterization and catalytic activity of thiol-MCM-41 materials synthesized using an improved method of preparation. This novel method of synthesis includes the partial replacement of the surfactant used previously — hexadecyltrimethylammonium bromide, for a shorter chain surfactant such as dodecyltrimethylammonium bromide. It also includes the use of tetramethylammonium hydroxide (TMAOH) as co-structuring agent instead of NaOH. The materials obtained from this modified gels present a higher order in the channels arrangement confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. These materials incorporates an important amount of thiol groups which can be oxidized with H2O2 in order to obtain the corresponding sulfonic groups, with a very strong acidity. The catalysts so obtained have been tested in the esterification of glycerol with fatty acids — oleic and lauric. The results obtained indicate that the catalysts prepared with mixtures of surfactants are more selective to the monoglycerides than the ones synthesized only with hexadecyltrimethylammonium bromide, probably due to the higher order in the channels packing.