Hybrid Organic-Inorganic Active Sites for Selective Heterogeneous Catalysis

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0854560 KatzEmerging applications of heterogeneous catalysis require the development of new materials that i) afford high catalyst selectivity and activity at the relatively low temperatures required to avoid background degradation reactions of critical chemical intermediates, and ii) function without leaching/degradation in aqueous and harsh organic solvent environments. This work addresses the pressing needs in (i) and (ii) above via the design and synthesis of heterogeneous catalysts consisting of multifunctional organic active sites. The organic component of these active sites inherently lends them to being hydrolytically stable while simultaneously providing tailorability of molecular structure for control of function. The intellectual merit of this research is to implement emerging concepts in the synthesis of organic acid and base active sites as relevant precursors for highly selective, active, and robust heterogeneous catalysts, which consist of a hybrid organic-inorganic material. The work specifically exploits the confinement of catalytic sites on the surface of silica and control reactivity of the resulting confined functional groups using calixarenes as an organizational scaffold and confinement entity.Upon calixarene grafting, lateral metathesis polymerization of anchored calixarenes on the inorganic-oxide surface synthesizes a robust two-dimensional crosslinked polymer consisting of immobilized catalytically active sites. This polymer is insoluble and is therefore expected to be leach-proof even under severe solvent environments, such as those involving high temperatures and aqueous solvent systems. Preliminary experiments aimed at demonstrating proof of concept are geared towards demonstrating robust and highly selective aldol condensation activity, a reaction that is key to fine chemicals and biorefining, in a variety of solvent environments using a recoverable catalyst, as well as the synthesis of enantioselective acid-base bifunctional catalysts based on this concept.These goals require the development of confined calixarene active sites containing acidic functionality, as well as sites containing base, which are attainable using procedures recently developed by our research group. Acid active sites will be investigated for reactions relevant to biorefining such as transesterification and ester hydrolysis. We further develop approaches to pattern the surface of an inorganic oxide, using silica as a model inorganic-oxide, with two disparate chemical functional groups, because methods of site isolation discovered during this process are likely to be generally applicable to other catalytic systems of relevance to other transformations, such as those involving supported metal and inorganic-oxide nanoparticles. The research activities broadly impact the training of future scientists in catalyst design and synthesis, with specific emphasis on structural characterization and functional assessment of hybrid organic-inorganic catalysts with designed nanoscale structure and connectivity. The training of graduate and undergraduate students will have special emphasis placed on the recruitment of female and minority students. Outreach activities include a K-12 component, with a focus on encouraging Pacific Islander minorities to pursue study of the chemical sciences and engineering, through inspirational research presentations to high-school students on the topic of future directions and challenges in and research while simultaneously providing a demonstration of how scientific discoveries can be used for creating new technology and understanding.