Surface Plasmon Resonant Gold-Palladium Bimetallic Nanoparticles for Promoting Catalytic Oxidation
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.222
Surface Plasmon Resonant Gold-Palladium Bimetallic Nanoparticles for Promoting Catalytic Oxidation Jonathan Boltersdorf,*,1 Asher C. Leff, 1,2 Gregory T. Forcherio,1 Joshua P. McClure,1 and Cynthia A. Lundgren1 1 United States Army Research Laboratory, Sensors and Electron Devices Directorate, Adelphi, MD 20783-1138, USA 2
General Technical Services, Adelphi, MD 20783-1138, USA
ABSTRACT
Colloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (CC) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.
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INTRODUCTION The interfacing noble metal (e.g., Pt) and metal oxide (e.g., RuO2) nanoparticles as cocatalysts has been extensively used as a technique to maximize the charge separation and spatial separation of the redox active sites for a semiconductor photocatalyst.[1-3] Recently, noble metal nanoparticles exhibiting surface plasmon resonances (SPR) have been integrated with traditional metal oxide photocatalysts (e.g., TiO2, Fe2O3) as a photosensitization strategy to enhance charge carrier generation/separation and photothermal conversion.[4-9] Excitation of the SPR induces coherent electron oscillations that amplify the local electric field and absorption crosssection. Energetic “hot” electrons are generated by the Landau dephasing of the absorptive SPR (1-100 fs) and transiently populate high energy states. Harnessing “hot” electrons from plasmonic materials is essential for enhancing local photochemical redox reactions. Additionally, the Ohmic relaxation of the “hot” electrons (100 fs to 1 ps) affo
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