Determining the catalytic activity and the reaction kinetics are key issues when new catalysts are developed, characterized, and introduced. Catalysis at the nanoscale employing nanoparticles has great potential because of their new catalytic properties, high surface-to-volume ratios, and high surface reactivity. [1] In principle, reactions at the surface of metal structures can be studied using molecular surfacespecific spectroscopic techniques. [2] The most versatile of these is surface-enhanced Raman scattering (SERS), which has been frequently applied in investigations of different types of reactions at electrochemical interfaces in situ [3] to address, for example, the formation of reaction intermediates, [4] the dependence of electroorganic reactions on electrode potential, [5] and electron transfer in protein systems. [6] Herein we demonstrate that SERS can be used to study directly the kinetics of a catalytic reaction in situ. Our approach is novel by allowing the structural characterization of the reactant and product surface species in the reaction as well as investigating rate constants in the same experiment. This was possible by using separate gold and platinum nanoparticles that were simultaneously attached to the same glass surface. Our method is independent of the optical absorption properties of the reaction products and/or the catalysts.In order to investigate a metal-catalyzed reaction with SERS or other plasmon-supported approaches, [7] bifunctional metal structures are needed that have plasmonic properties and also act as a catalyst. [8] A number of catalytically active composite nanostructures have been reported to enhance the Raman signals of dye molecules, [9] and SERS has been used to monitor the structural evolution of bimetallic catalytically active Au-Pt nanoparticles. [10] However, direct observations of a catalytic process by SERS have been rare as they require bifunctional nanomaterials. [11] Our approach is different from those previously reported based on composite nanostructures with plasmonic (Au) and catalytic (Pt, [11a] or Pd) [11b] properties, as we have used separate gold and platinum nanoparticles that are simultaneously immobilized on a glass surface. Scanning tunneling microscopy (STM) data indicate that owing to the proximity of the platinum and gold nanoparticles, the molecules can interact with the platinum nanoparticles whilst they reside in the local optical fields provided by the localized surface plasmons of the gold nanoparticles. The versatility, stability, and general applicability of the immobilized gold nanoparticles for studying catalytic reactions are demonstrated by the quantification of the reaction products and the determination of the kinetics with different catalysts. The results reported therefore have implications both for basic catalysis research and analytical applications.Gold nanoparticles 40 nm in diameter and platinum nanoparticles less than 2 nm in diameter were prepared by reported procedures. [12] Mixtures of these gold and platinum nano...

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The structure and ultrafast photodynamics of ~8 nm Au@Pt core-shell nanocrystals with ultrathin (<3 atomic layers) Pt-Au alloy shells are investigated to show that they meet the design principles for efficient bimetallic plasmonic photocatalysis. Photoelectron spectra recorded at two different photon energies are used to determine the radial concentration profile of the Pt-Au shell and the electron density near the Fermi energy, which play a key role in plasmon damping and electronic and thermal conductivity. Transient absorption measurements track the flow of energy from the plasmonic core to the electronic manifold of the Pt shell and back to the lattice of the core in the form of heat. We show that strong coupling to the high density of Pt(d) electrons at the Fermi level leads to accelerated dephasing of the Au plasmon on the femtosecond timescale, electron-electron energy transfer from Au(sp) core electrons to Pt(d) shell electrons on sub-picosecond timescale, and enhanced thermal resistance on the 50 ps timescale. Electron-electron scattering efficiently funnels hot carriers into the ultrathin catalytically active shell at the nanocrystal surface, making them available to drive chemical reactions before losing energy to the lattice via electron-phonon scattering on the 2 ps timescale. The combination of strong broadband light absorption, enhanced electromagnetic fields at the catalytic metal sites, and efficient delivery of hot carriers to the catalyst surface make core-shell nanocrystals with plasmonic metal cores and ultrathin catalytic metal shells promising nanostructures for the realization of high-efficiency plasmonic catalysts.

Well-defined CuO nanoparticles are presented as catalysts in a new noble metal-free and green reaction protocol for carbonyl compound synthesis.

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Aucore/Ptshell–graphene catalysts (G‐Cys‐Au@Pt) are prepared through chemical and surface chemical reactions. Au–Pt core–shell nanoparticles (Au@Pt NPs) covalently immobilized on graphene (G) are efficient electrocatalysts in low‐temperature polymer electrolyte membrane fuel cells. The 9.5 ± 2 nm Au@Pt NPs with atomically thin Pt shells are attached on graphene via l‐cysteine (Cys), which serves as linkers controlling NP loading and dispersion, enhancing the Au@Pt NP stability, and facilitating interfacial electron transfer. The increased activity of G‐Cys‐Au@Pt, compared to non‐chemically immobilized G‐Au@Pt and commercial platinum NPs catalyst (C‐Pt), is a result of (1) the tailored electron transfer pathways of covalent bonds integrating Au@Pt NPs into the graphene framework, and (2) synergetic electronic effects of atomically thin Pt shells on Au cores. Enhanced electrocatalytic oxidation of formic acid, methanol, and ethanol is observed as higher specific currents and increased stability of G‐Cys‐Au@Pt compared to G‐Au@Pt and C–Pt. Oxygen reduction on G‐Cys‐Au@Pt occurs at 25 mV lower potential and 43 A gPt−1 higher current (at 0.9 V vs reversible hydrogen electrode) than for C–Pt. Functional tests in direct fomic acid, methanol and ethanol fuel cells exhibit 95%, 53%, and 107% increased power densities for G‐Cys‐Au@Pt over C–Pt, respectively.

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