(439c) Structure-Acvitiy Relationships for Zirconia-Based Catalysts

In this talk we will present our recent studies of how the local structure of Zr-sites in zirconia-based catalysts affect their activity and selectivity for reactions important in the upgrading of biomass-derived molecules. Zr site structures were varied using single crystal surfaces, ZrO₂ particles infiltrated into high surface area supports, and ultra-thin ZrO₂ films on oxide supports. The latter involved the use of atomic layer deposition (ALD) to produce conformal ZrO₂ films less than 2 nm in thickness, as well as isolated Zr sites. Specific examples that will be presented include structure-activity relationships for the dehydra-decylcization of cyclic ethers, transfer hydrogenation and etherification of hydroxymethylfurfural, and Diels–Alder cycloaddition of ethylene to dimethylfuran. In all cases dimensionally confined ZrO₂ exhibited catalytic properties that varied significantly from that of the bulk oxide. For example, the activity and selectivity for the dehydra-decylcization of THF to produce butadiene was found to increase with ZrO₂ film thickness in the nanometer regime. The opposite trend was observed, however, for cycloaddition of ethylene to dimethylfuran, where bulk ZrO₂ was nearly inactive, while nm thick ZrO₂ films in SBA-15 and isolated Zr sites substituted into zeolite beta both exhibited high activity for this reaction. The insights these results provide for identifying the active sites on ZrO₂ surfaces will be discussed.