We have developed a synthetic strategy for multifunctionalization of mesoporous silica nanoparticle (MSN) materials. This method allows us to tune the relative ratio of different functional groups and the resulting particle morphology of MSNs. By introducing two organoalkoxysilanes as precursors in the co-condensation reaction, we can utilize one precursor with stronger structure-directing ability to create the desired pore and particle morphology and employ the other for selective immobilization of catalysts. As a proof of principle, we have synthesized and reported a series of bifunctionalized MSN-based heterogeneous catalysts for a variety of carbonyl activation reactions, such as aldol, Henry and cyanosilylation reactions. By varying the secondary group in the bifunctionalized MSN catalysts, we discovered that the selectivity of a nitroaldol reaction of two competing benzaldehydes reacting with nitromethane could be systematically tuned simply by varying the physicochemical properties of the pore surface-bound secondary groups, i.e. polarity and hydrophobicity. By further utilizing this Gate-Keeping approach, we have developed a mesoporous silica-based catalytic system that is able to regulate the enantioselectivity of a variety of reactions.

Furthermore, we have reported a biomimetic cooperative catalytic system comprised of a series of bifunctionalized MSN materials with various relative concentrations of a general acid and a base group. We were inspired by the fact that enzymes engaged in carbonyl chemistry often employ both general acid and base catalytic residues in the active sites to cooperatively activate specific substrates. In this system, we have demonstrated that the general acid functionality could cooperatively activate substrates with the basic group in catalyzing various reactions that involve carbonyl activation. In addition to the organically functionalized MSN, we have developed a mixed oxide catalyst that contains both Lewis acidic and basic sites for the synthesis of biodiesel from various free fatty acid (FFA)-containing oil feedstocks. We have demonstrated that the acid and base functionalities could cooperatively catalyze both the esterification of FFAs and the transesterification of oils with short-chain alcohols (e.g. methanol and ethanol) to form alkyl esters (biodiesel). We envision that these multifunctionalized MSNs could serve as new selective catalysts for many other important reactions.

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