Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H03: Supported Nano-Clusters IV: Cluster Catalysis and ElectrocatalysisFocus
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Sponsoring Units: DCP Chair: Beatriz Roldan Cuenya, Univ of Central Florida Room: LACC 150C |
Tuesday, March 6, 2018 2:30PM - 3:06PM |
H03.00001: Supported Au nanoparticles: good for methanol decomposition or formation? Invited Speaker: Talat Rahman In the three decades since Haruta’s discovery of the unexpected reactivity of oxide-supported Au nanoparticles, we have come a long way in the application of nanoparticles as catalysts for a variety of reactions. Yet, the phenomenon is far from being fully understood as a number of factors control both the reactivity and the product selectivity of these nanocatalysts: the size, the shape, the support, the coadsorbates are all found to play a role. In this talk, I will compare and contrast the local electronic structural and geometric environments for the active sites on Au nanoparticles, on three different supports: single-layer MoS 2 , single-layer h-BN and the TiO 2 (110) surface. I will show that while the interface plays a major role in methanol decomposition [1] and CO oxidation facilitated by Au nanoparticles supported on TiO 2 (110), the same is not the case when these nanoparticles are supported on single-layer MoS 2 , single- layer h-BN. In fact, the Au/MoS 2 composite favors the formation of methanol (and higher alcohols) from syn gas [2]. I will trace these differences to the Au-support interaction, the ensuing charge transfer, the role of vacancies, and the extent to which the system frontier orbitals are shifted towards the Fermi level.\\ \\ [1] S. Hong and T. S. Rahman, JACS, 135, 7629 (2013)\\ [2] T. B. Rawal, D. Le, and T. S. Rahman, J. Phys.: Condens. Matter 29 415201 (2017). |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H03.00002: Computational Study of Electrochemical Reduction of CO2 on Supported Bimetallic Clusters Haiying He, Christopher Morrissey, Marcus Ochsendorf, Peter Zapol Electrochemical conversion of CO2 into useful chemicals or fuels offers a route to sustainability, which is largely hampered by the relatively high overpotential and/or low selectivity. Supported subnanometer metal clusters, which have demonstrated unique electrocatalytic properties, provide a large composition and size space for optimization of these properties. In this study, we have screened electrochemical properties of bimetallic clusters on different defective graphene supports as possible catalysts for the electrochemical reduction of CO2 using first-principles based approach. Trends in variation of the catalytic behavior with the composition, size of the cluster and the nature of the support are presented. Potential candidates for improved electrochemical performance are identified. The interesting interplay of the cluster and the support at the interface shed light on the variation in the electronic properties and chemical reactivity of the cluster. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H03.00003: Alkali-Metal Promotion of Mass-Selected Metal Sulfide Nanoclusters on Au(111) for CO2 Activation Meng Xue, Yilin Ma, Ping Liu, Michael White Molybdenum sulfide promoted by alkali (K, Cs) and/or transition (Ni, Co) metals is known to catalyze syngas (CO+H2) to alcohols. The hydrogenation of CO2 to oxygenates on metal sulfides is less well studied, but is of current interest for recycling CO2 into liquid fuels. Recent density functional calculations suggest that alkali-modified Mo6S8 clusters (unsupported) are active for CO2 hydrogenation to methanol. In this work, we are using mass-selected cluster deposition to study the activation of CO2 on K-modified, metal sulfide nanoclusters supported on Au(111). The clusters are prepared by reactive sputtering (3% H2S in Ar) of a metal target (Mo, W), mass-selected by a quadrupole filter and then soft-landed onto an Au(111) crystal. Thermal desorption measurements show that CO2 exposure of the K/Mo6S8/Au(111) surface leads to two distinct CO2 desorption peaks (350 K, 450 K), which are not present for surfaces with only K-atoms or Mo6S8 clusters. Similar experiments were carried out for other Mo and W sulfide clusters. The experimental results are compared with DFT calculations of CO2 binding on the K/Mo6S8/Au(111) surface. |
Tuesday, March 6, 2018 3:30PM - 4:06PM |
H03.00004: Visualizing bimetallic effect and plasmonic catalytic hotspots on single nanocatalysts via correlated super-resolution and electron microscopy Invited Speaker: Peng Chen I will present our latest efforts in using correlated super-resolution fluorescence microscopy of catalysis and scanning electron microscopy to visualize two nanoscale catalytic phenomena on single nanocatalysts. In one, we quantitatively visualize the enhanced bimetallic activity at a well-defined metal-metal interface within single bimetallic nanoparticles, in direct comparison with those at non-interface regions within the same nanocatalyst. In the other, we quantitatively visualize the surface-plasmon-enhanced catalytic activity at nanoscale gaps within a single plasmonic nanostructure, in direct comparison with those at non-gap regions. In both cases, localized catalytic enhancements are spatially resolved under operando conditions. Analyses of the results further lead to insights into the enhancement mechanisms at bimetallic sites and plasmonic hotspots, respectively. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H03.00005: Photoinduced Dehydrogenation of a Single Molecule Adsorbed on a Surface Likun Wang, Siyu Chen, Shaowei Li, Wilson Ho Photons can be coupled with tunneling electrons to induce a chemical reaction of a molecule adsorbed on a surface in the junction of a scanning tunneling microscope (STM). Here, by using the combination of a low temperature STM with a femtosecond laser, we demonstrated the control and characterization of the dehydrogenation in a unimolecular reaction with atomic scale resolution. A single acetylene (HCCH) molecule can be sequentially dehydrogenated into ethynyl (CCH) and dicarbon (CC). While both reaction steps can be induced by tunneling electrons, only the C-H bond activation of the ethynyl could also be proceeded by the coupling of the tunneling electron with a photon. These studies provide us new insights into single molecule photochemistry with atomic scale precision. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H03.00006: Mechanisms of Photocatalytic H2 Evolution on Co-Catalyst Loaded Semiconductors in the UHV Constantin Walenta, Sebastian Kollmannsberger, Carla Courtois, Rui Pereira, Martin Stutzmann, Martin Tschurl, Ueli Heiz Despite of intense research efforts in the last decade, photocatalytic processes for the generation of renewable fuels are still lacking the requirements for successful application on industrial scale. Research strategies have so far been focused on material screening due to the complexity of the underlying processes. However, a deep fundamental understanding will ultimately allow us to implement knowledge-based improvements towards enhanced photocatalytic efficiencies, selectivities and stabilities. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H03.00007: Enhancement of Water Oxidation Activity by Size-Selected Sub-10 nm Manganese Oxide Nanoparticles Malak Khojasteh, Shima Haghighat, Vitaly Kresin, Jahan Dawlaty Emulating photosynthetic water oxidation by using inorganic metal oxides has been a long-standing challenge. In plants photoexcitation is collected by chlorophylls and funneled into a cluster composed of manganese, oxygen, and calcium, known as the oxygen evolving complex. This natural complex provides motivation to explore artificial materials that use manganese oxide nanoparticles as electrocatalysts or photocatalysts. We approached this goal by soft-landing size-selected 4, 6, and 8 nm manganese nanoparticles, produced by a sputtering/aggregation nanocluster source, onto conducting electrodes. We then used these clusters as electrocatalysts for water oxidation. The water oxidation threshold revealed a significant decrease with decreasing particle size. XPS spectroscopy identified the final stoichiometry of the catalytically active nanoparticles, after exposure to air, as MnO. The ability of a sub-monolayer film of such sub-10 nm nanoparticles to effectively promote the catalytic process is noteworthy and demonstrates the influence of nanoscale size effects on their electronic structure. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H03.00008: Tuning the Hydrogen Evolution Reaction Activity of MoC-Supported Graphene Using Defect and N-doping Timothy Yang, Wissam Saidi The hydrogen evolution reaction (HER) of MoC-supported graphene is studied using density functional theory in conjunction with a thermodynamic approach and a kinetic model for the exchange current density. We verify that MoC (001) is one of the most stable surface terminations at standard conditions and can be strongly coupled with graphene. Our main finding is that the MoC-supported graphene heterostructure has an optimal HER activity that can be tuned through the interplay of nitrogen dopants and defects on graphene. We further determine the overpotential, rate limiting step, and minimum reaction pathways for HER mechanism in acidic environment. |
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