Development and Characterization of Catalytic Systems for Biomass-Derived Chemical Feedstocks

Citation

Orazov, Marat (2017) Development and Characterization of Catalytic Systems for Biomass-Derived Chemical Feedstocks. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9X63JZZ. https://resolver.caltech.edu/CaltechTHESIS:07202016-150438490

Abstract

Heterogeneous catalysis by Brønsted and/or Lewis acid sites isolated within microporous environments is a topic that is perpetually growing in scope and importance. While Brønsted acid sites in zeolites have been studied and applied extensively in the petrochemical industry, new opportunities for green processes based on renewable chemical feedstocks call for applications of new microporous materials that possess Lewis acid sites (e.g., zeotypes with framework Sn, Ti, Zr, or Hf). Characterization of such materials and the specific structures of the Lewis acid sites provides insights for rational catalyst design and application.

This work provides experimental evidence for the identities of the active sites in Sn-Beta zeotype for the 1,2-intramolecular hydride shift (1,2-HS) reaction that results in D-glucose isomerization to D-fructose, and for the 1,2-intramolecular carbon shift (1,2-CS) reaction that results in D-glucose isomerization to D-mannose. Specifically, by selective poisoning experiments, the partially-hydrolyzed, "open" Sn site is shown to be the active site for the 1,2-HS reaction. The participation of the proximal silanol of such an open Sn site in the 1,2-HS reaction is demonstrated thorough alkali-exchange experiments. Such experiments also reveal that the active site for the 1,2-CS reaction is an open Sn site with a cation-exchanged proximal silanol.

1,2-CS catalysts, in general, are shown to also catalyze retro-aldol reactions of hexoses at moderate temperatures (ca. 100 °C), and to be compatible with microporous 1,2-HS catalysts in tandem catalytic schemes that enable production of alkyl lactates.

Finally, the Lewis acidity of framework Zn in zincosilicate microporous materials is demonstrated through probe-molecule infrared spectroscopy. One such material is then shown to catalyze Diels-Alder cycloaddition-dehydration reactions of oxygenated furans and ethylene. To the best of our knowledge, these materials are the first heterogeneous catalysts reported to catalyze the direct formation of terephthalate esters from ethylene and dimethyl 2,5-furandicarboxylate with appreciable selectivity.

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