Sum Frequency Generation (SFG), a form of surface-sensitive vibrational spectroscopy, has emerged as an invaluable tool to characterize chemistry on the surface of heterogenous metal catalysts. More recently, research in heterogeneous catalysis has moved away from perfect single crystals to model nanoparticles made in colloidal synthesis. SFG studies on nanoparticles have been restrained by a single question: how do you extract the signal of an adsorbate from the signal of the organic capping agent? Initially, gentle cap removal, with UV-ozone for example, seemed like the best option. Cap-free nanoparticles are much less stable under reaction conditions. In addition, we show cap removal causes varied pathways for the cyclohexene hydrogenation reaction even when no aggregation occurs. In order to get the best representation of the kinetics which occurs on colloidal nanoparticles used on mesoporous supports, the capping agent should remain intact. We demonstrate that the SFG signal of the cap is substantially reduced in the presence of hydrogen, allowing the reactive adsorbate to be clearly resolved. Cyclohexene hydrogenation, ethylene hydrogenation and cis-2-butene hydrogenation reactions are characterized using this method. This work offers the first vibrational spectroscopy results of intermediates on PVP-capped Pt nanoparticles with no cap removal other than standard washing procedures.

Sum frequency generation on heavily washed PVP-capped Pt nanoparticles

243rd National Meeting (2012)

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