(594g) Constraining Local Environments in Oxide Catalysts

Steric confinement of adsorbed reactants, transition states, or products can significantly alter reaction trajectories in otherwise identical active sites. Confinement effects are well-recognized, if incompletely understood, in microporous acid catalysts, but are also present for other types of catalysts. In this presentation, we will discuss how steric effects can be engineered into oxide active sites, specifically zirconium oxides. In one set of examples, it will be shown how the specific coordination environment around zirconium oxide-based metal organic frameworks (MOFs) influences selectivities in olefin hydrogenation / isomerization and in hydrogen transfer reactions. Reactants are generally much smaller than the available pore volume, so we ascribe changes in selectivity to altered coordination patterns around the oxide cluster active site. In a second set of examples, molecule-templated atomic layer deposition of a nominally-inert sieving oxide is used to control the available space around a single atom active site, either Zr or Ti. Depending on tunable parameters such as metal density, template size, and extent of deposition, selectivities and rates can be controlled in selective oxidation and hydrogen transfer reactions. Again, reactants are much smaller than the bulk porosity present, indicating control over the local active site environment independent of the average pore size.