Development of niobium containing acidic catalysts for glycerol esterification

Mesoporous silicate and niobiosilicate materials of SBA-15 type were prepared and post-synthesis modified with MPTMS, i.e. (3-mercaptopropyl)trimethoxysilane, followed by oxidation of thiol species. The samples obtained were characterised by different techniques (N2 adsorption/desorption, XRD, elemental and thermal analyses) and applied as catalysts in glycerol esterification with acetic acid. The focus was on the comparison of the role of niobium in the formation of sulphonic species and its stability in the post-synthesis modified materials (prepared within this work) with those, already published, prepared by one-pot synthesis method. The most important finding is that the presence of niobium in the SBA-15 structure improves the efficiency of –SH oxidation by hydrogen peroxide towards sulphonic species like in case of one-pot synthesised samples. However, contrary to the latter samples the presence of niobium does not increase the stability of the modifier (oxidized MPTMS). This has an impact on faster deactivation of samples prepared. Samples prepared with post-synthesis modification exhibit much higher activity in glycerol esterification.

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► Niobium in the material structure enhances the formation of sulphonic species.
► Stability of sulphonic species does not depend on the chemical composition of SBA-15.
► 40% of selectivity to triacetylglycerol is reached.