(483b) Selectivity Control by Modification of Supported Metal Catalysts with Alkanethiol Monolayers
Performing selective conversions of reagents with multiple functional groups is a challenging objective, since each functional group can potentially adsorb and react on a catalytic surface. Our group has explored several techniques for aligning multifunctional molecules above catalytic surfaces to promote selective reaction of a particular functional group. One such approach involves the modification of supported metal catalysts with organic ligands such as alkanethiols. Alkanethiols can be deposited on metal surfaces to form organized self-assembled monolayers (SAMs) that can potentially cause reagent molecules to adopt particular orientations above the metal surface, altering selectivity. We have recently shown that such a strategy can be applied to technical supported catalysts such as Pd/Al2O3. For example, this attachment strategy has resulted in an increase in the selectivity to the desired product during 1-epoxy-3-butene (EpB) hydrogenation from <20% on an uncoated catalyst to >90% on a SAM-coated catalyst at equivalent reaction conditions and conversion. This dramatic change in selectivity is supported by surface science experiments which show that a Pd(111) surface covered with alkanethiol SAMs causes EpB to adsorb in a configuration that strongly disfavors epoxide ring opening. In this contribution, the effect of self-assembled monolayers on the surface chemistry and hydrogenation catalysis of several compounds will be discussed, including EpB, crotonaldehyde, and acetylene. Furthermore, experiments aimed at identifying the mechanisms behind observed selectivity and activity trends will be described.