(22i) Optically Excited Plasmonic Metal Nanostructures As Selective Direct Propylene and Ethylene Epoxidation Catalysts

In this contribution, we demonstrate that plasmonic silver and copper catalysts, optically excited with low intensity (order of Solar intensity) visible light, can achieve significantly higher selectivity compared to other conventional heterogeneous catalysts in the direct epoxidation (using O₂ as an oxidant) of propylene and ethylene to form propylene and ethylene oxide respectively.

We will show that the underlying mechanisms governing bond making (breaking) on optically excited plasmonic metals are fundamentally different than on semiconductors and those related to classical thermo-catalytic processes. Consequently, plasmonic metals exhibit profoundly different behavior. For example, unlike semiconductors, these materials exhibit a positive relationship between reaction rates (and quantum efficiencies) and light intensity. Also, plasmonic nanostructures exhibit an exponential increase of photo-catalytic rate (and quantum efficiency) on operating temperature.

We have developed a molecular model based on first-principles calculations that describes photo-chemical transformations on plasmonic metals. We show that the model captures the unique, experimentally observed features of the photo-catalytic processes on plasmonic metals.

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