Probing support-solvent-solute interactions in heterogeneous catalysts by surface-sensitive magnetic resonance tools

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The manufacturing of chemicals from renewable biomass is an important, long term alternative to petroleum. Co-production of higher-value chemicals can also help to make these processes more economical. However, biomass has a high oxygen content. To make useful chemicals, this oxygen must first be removed. Dehydration is one important route to reducing oxygen content. With this funding from the NSF Division of Chemistry, Drs. Han and Scott of the University of California Santa Barbara are investigating these dehydration reactions. The role of solvents and catalysts are being studied to aid in the design of more effective catalysts for these reactions. At the same time, powerful new measurement methods for probing the fundamental chemistry are being developed. The graduate students on the project are acquiring advanced research skills, and learning to integrate their findings with collaborators. They are also gaining international and industrial perspectives of their research. The PIs and their students are mentoring younger, at-risk students, who are also experiencing first-hand experimental problem-solving.The efficient conversion of biomass-derived polyols to value-added renewable chemicals by dehydration is an important challenge for heterogeneous catalysis. Conducting such reactions selectively in semi-aqueous solvent systems, under mild reaction conditions, requires the development of highly active, hydrothermally stable catalysts. Their activity can be enhanced by tuning the solvent composition and the catalyst support to promote the partitioning of dissolved reactant molecules to the catalytically active solid, and adsorbed product molecules back into solution. This project elucidates and quantifies the interdependent solid-solvent-solute interactions that control activity and selectivity in catalytic dehydration reactions. In the presence of solid catalysts for acid-catalyzed alcohol dehydration reactions, the dynamics of adsorbed reactants and products, the surface-coupled solvent dynamics, and the partitioning of (co-)solutes to the surface relative to bulk, are being characterized with molecular precision. The measurements are made possible by state-of-the-art, surface-sensitive magnetic resonance tools, including solid-state magic-angle spinning (MAS) dynamic nuclear polarization (DNP) NMR to characterize catalyst supports and active sites with dramatically enhanced sensitivity, and Overhauser DNP to measure the surface diffusivity of solvent molecules which is correlated with the solvation barrier to adsorption. The key questions being addressed are: (1) How can catalytic activity and selectivity in polyol dehydration be controlled, by varying the solvation barrier for solute adsorption to the catalyst surface? (2) How can the solvation barrier for solute approach be modulated, by tuning the hydrophobicity of the catalyst surface and the composition of the solvent mixture? The study generates a basis for new structure-property-function relationships in liquid-phase heterogeneous catalysis, exploring their validity in an important family of reactions for the upgrading of biomass-derived polyols, and advancing the development of surface-sensitive magnetic resonance-based tools to characterize heterogeneous catalysts. The graduate students involved with the project are learning advanced research techniques, and learning to integrate their findings with collaborators. They are also gaining international and industrial perspectives of their research. The PIs and their students are mentoring younger, at-risk students, who themselves are experiencing first-hand experimental problem-solving.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.