Critical assessment of the base catalysis properties of amino-functionalized mesoporous polymer-SBA-15 nanocomposites

Abstract

Surface engineering of mesoporous materials is essential for the development of highly selective sorbents, catalysts or drug delivery systems. In the present work, mesoporous amine-functionalized polymer-silica composites are synthesized using a two-step pore surface-confined polymerization technique, and characterized by N2 sorption, coupled thermogravimetric analysis (TG/DTA-MS), elemental CHN analysis, solid state 13C NMR spectroscopy, attenuated total reflectance infrared spectroscopy (ATR-IR) and zeta potential titration. From the results, it is clear that the synthesis method is particularly appropriate to control the location and distribution of the functional groups within the mesopores. The base catalytic properties of the functional nanocomposites were evaluated in model aldol-type reactions, i.e., Knoevenagel reaction, nitroaldol (Henry reaction) and Claisen-Schmidt condensations, as well as in the Michael addition. The catalytic behavior of the synthesized nanocomposites was compared with reference samples, that is, materials obtained via standard grafting procedures and co-condensation synthesis. Herein, a critical assessment of the catalytic activity and stability of the composite catalysts is performed in comparison to the reference materials. In general, the mesoporous composites are shown to be active catalysts for the reactions studied. In comparison with the reference samples (e.g., grafted materials), their activity per mass of catalyst, was similar, however, when comparison was made based on the amine content, the composite materials showed superior activity. This contribution provides new insights into the design of large pore mesoporous catalysts and sorbents possessing base properties.