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  1. HET/RIKEN Lunch Seminar

    12:30 pm, Building 510, Room 2-160

    Hosted by: Mattia Bruno and Enrico Rinaldi

    Quantum simulation proposes to use future quantum computers to calculate properties of quantum systems. In the context of chemistry, the target is the electronic structure problem: determination of the electronic energy given the nuclear coordinates of a molecule. Since 2006 we have been studying quantum approaches to quantum chemical problems, and such approaches must face the challenges of high, but fixed, precision requirements, and fermion antisymmetry. I will describe several algorithmic developments in this area including improvements upon the Jordan Wigner transformation, alternatives to phase estimation, adiabatic quantum computing approaches to the electronic structure problem, methods based on sparse Hamiltonian simulation techniques and the potential for experiments realizing these algorithms in the near future. I will also briefly review work by others on the analog and digital simulation of lattice gauge theories using quantum simulators.


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  1. HET/RIKEN Lunch Seminar

    "Quantum Simulation from Quantum Chemistry to Quantum Chromodynamics"

    Presented by Peter Love, Tufts

    Thursday, May 10, 2018, 12:30 pm
    Building 510, Room 2-160

    Hosted by: Mattia Bruno and Enrico Rinaldi

    Quantum simulation proposes to use future quantum computers to calculate properties of quantum systems. In the context of chemistry, the target is the electronic structure problem: determination of the electronic energy given the nuclear coordinates of a molecule. Since 2006 we have been studying quantum approaches to quantum chemical problems, and such approaches must face the challenges of high, but fixed, precision requirements, and fermion antisymmetry. I will describe several algorithmic developments in this area including improvements upon the Jordan Wigner transformation, alternatives to phase estimation, adiabatic quantum computing approaches to the electronic structure problem, methods based on sparse Hamiltonian simulation techniques and the potential for experiments realizing these algorithms in the near future. I will also briefly review work by others on the analog and digital simulation of lattice gauge theories using quantum simulators.

  2. Condensed-Matter Physics & Materials Science Seminar

    "Chemistry beyond the crystal- advanced Fourier techniques"

    Presented by Simon Kimber, Oak Ridge National Laboratory

    Monday, April 30, 2018, 1:30 pm
    ISB Bldg. 734 Conf. Rm. 201 (upstairs)

    Hosted by: Ian Robinson

    Chemical crystallography nowadays makes structure determination and refinement trivial. However, advances in x-ray and neutron sources mean that we should revisit some of the basic assumptions that shape our experiments. For example, most chemical reactivity in e.g. catalysis, self-assembly etc, occurs in the solution phase. Why are we as crystallographers then wedded to the solid state? In this presentation, I will show how total scattering can be used to determine changes in cluster structure during photochemical reactions and to probe the role of the solvent in 'magic size' cluster formation. I will then describe how neutron scattering techniques can be used to challenge another basic assumption- the static approximation in total scattering. We have successfully applied so-called 'dynamic-PDF' techniques to simple chalcogenide materials. This allows to determine the time scale on which local distortions appear, providing insight into the role of highly anharmonic phonons in e.g. phase change and thermoelectric materials. Time allowing, I will also provide a short update on progress at ORNL, including the upcoming restart of the SNS, and new instrumentation for diffraction, total and diffuse scattering.

  3. Center for Functional Nanomaterials Seminar

    "Electrocatalysis: From nanoelectrochemistry to materials design"

    Presented by Professor Dr. Wolfgang Schuhmann, Ruhr-Universität Bochum, Analytical Chemistry and Center for Electrochemical Sciences (CES), Germany

    Friday, April 27, 2018, 11 am
    Bldg 735, CFN, Seminar Room 2nd Floor

    Hosted by: Huolin Xin

  4. Chemistry Department Seminar

    "Spectroscopy and Diabatization: Turning the GMH Method Upside Down to Study Butadiene"

    Presented by Robert Cave, Harvey Mudd College

    Friday, April 27, 2018, 11 am
    Room 300, 3rd Floor, Chemistry Bldg. 555

    Hosted by: John Miller

    The spectroscopy of the low-lying singlet states of butadiene has been a vexing problem for theorists for over forty years. The positions of the lowest-lying singlet states at the ground state geometry are something of a methodological Rorschach test and the planar stationary points of these states have seen modest attention. Important work has been done on the ultrafast dynamics of butadiene following excitation to the bright 11Bu but these studies are often forced to use simple wavefunctions that may lead to exaggerated couplings. We present new simulation results of its electronic spectrum based on Equations of Motion Coupled Cluster Theory in large basis sets using a vibronic coupling model involving many vibrational modes. We investigate the sensitivity of the results to the choice of vibronically-coupled states and test the dependence of the results on vertical excitation energies. We believe that butadiene should be considered somewhat less vexing than it has been before and our results can be used as a starting point for accurate explorations of its short-time excited state dynamics.

  5. Chemistry Department Seminar

    "In situ analysis of Ru-based catalysts under water oxidation conditions"

    Presented by Yulia Pushkar, Purdue University

    Tuesday, February 27, 2018, 10 am
    Room 300, 3rd Floor, Chemistry Bldg. 555

    Hosted by: Dmitry Polyansky

    Realization of artificial photosynthesis carries the promise of cheap and abundant energy. The water molecule is an ideal source of electrons and protons for fuel forming reactions, but the chemical complexity of water splitting makes practical realization challenging. To advance the catalyst's rational design, detailed information on the structure of the catalyst under reaction conditions and mechanisms of O-O bond formation are required. Here, we used a combination of EPR, freeze quench and stopped flow spectroscopy with ms-s time resolution, X-ray absorption spectroscopy (XAS), Resonance Raman (RR) and DFT to follow in situ catalyst dynamic under conditions of water oxidation.1-3 Two representative Ru –based catalysts were analyzed: [RuII(NPM)(4-pic)2(H2O)]2+ and [RuII(pic)2(dpp)]2+. First system has water coordinated to Ru center and forms [RuIV(NPM)(4-pic)2=O]2+ upon oxidation. This intermediate undergoes fast dynamics (on few sec time scale) of oxygen atom transfer from the RuIV=O oxo species to uncoordinated nitrogen of the NPM ligand. NPM ligand modification occurs on the time scale of catalyst activation and results in [RuIII(NPM-NO)(4-pic)2(H2O)]3+ and [RuIII(NPM-NO,NO)(4-pic)2]3+ complexes with unique EPR signals. [RuII(pic)2(dpp)]2+ complex was proposed to activate via formation of the 7-coordinate [RuV=O(pic)2(dpp)]3+ species. We report the first detection of the ligand protected 7-coordinate species in catalytic mixtures by combination of the spectroscopic techniques. Over a few minutes this intermediate transfers oxygen from the RuV=O group to a pyridyl nitrogen of the dpp ligand. This reaction proceeds twice resulting in the dpp-di-N-oxide ligand. This ligand modification results in the catalyst activation. [Ru(bda)(pic)2] complex is also proposed to activate via formation of 7-coordinate [RuV=O(bda)(pic)2]+ intermediate which is highly reactive in solution via radical coupling pathway. Site isolation of the catalyst on the electrode

  6. NSLS-II Friday Lunchtime Seminar Series

    "Using X-ray Fluorescence Microprobe to Elucidate the Chemistry of Trace Elements in Soils and Plants"

    Presented by Ryan Tappero, NSLS-II

    Friday, February 23, 2018, 12 pm
    NSLS-II Bldg. 743 Rm 156

    Hosted by: M. Abeykoon, S. Chodankar, B. Ocko, T. Tanabe, J. Thieme

  7. Chemistry Department Seminar

    "Learning the nanocatalyst structure "on the fly" using neural networks"

    Presented by Dr. Janis Timoshenko, Dept. of Material Science and Chemical Engineering, Stony Brook University

    Monday, February 12, 2018, 11 am
    Room 300, Chemistry Bldg. 555

    Hosted by: Sanjaya Senanayake

    Understanding of atomic structure in metallic nanoparticles (NPs) and its relation to the NPs properties is important for design of novel catalytic materials. In-situ studies are an essential element in such investigations, since the atomic structure of nanosized catalysts can change dramatically in reaction conditions. X-ray absorption spectroscopy is one of a few methods that are useful in this case, due to its sensitivity to the chemical state of absorbing atoms and to the types and arrangements of atoms around the absorber, and its suitability for in-situ and in-operando studies. While EXAFS spectroscopy is widely used in NPs structure studies, much less attention has been paid to the information encoded in X-ray absorption near edge structure (XANES). Analysis of XANES data has several advantages. First, XANES is less sensitive to disorder, which affects severely EXAFS quality and complicates EXAFS data interpretation. Secondly, XANES is more sensitive to the 3D geometry of the environment around absorbing atoms. Better signal-to-noise ratio in XANES region of absorption spectra also means that spectra can be collected with better time-resolution, for more diluted samples, on strongly attenuating support materials and/or in complex experimental setups. The main challenge that hinders the usage of XANES for quantitative analysis is the lack of methodology that would allow one to extract structural information from experimental data. Recent developments in data-enabled discovery methods provide a key to this problem. To correlate XANES features with the descriptors of 3D local structure of metallic NPs, we employed machine learning and ab-initio XANES calculations. Here we demonstrate the potentiality of this method on the example of XANES study of monometallic (Pt, Ag and Cu), as well as bimetallic (PdAu) particles. We use theoretical site-specific XANES spectra, calculated by ab-initio codes for a broad range of structure models, to train an artificial neura

  8. Chemistry Department Seminar

    "In situ Studies and Gas Phase Visulation of Model Catalysts at Work"

    Presented by Prof. Edvin Lundgren, Institute of Physics, Lund University, Sweden

    Wednesday, January 31, 2018, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Sanjaya Senanayake

    Motivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most studies have been performed in well-controlled environments, and has been instrumental for the present day understanding of catalysis. We have for some years explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. In this contribution we will show examples from catalytic CO oxidation over Pd single crystal surfaces using Ambient Pressure X-ray Photo emission Spectroscopy (APXPS) [1] and High Energy Surface X-Ray Diffraction (HESXRD) [2] at more realistic conditions. However, the detected surface structure during the reaction is sensitive to the composition of the gas phase close to the catalyst surface [3-4]. Therefore, the catalytic activity of the sample will itself affect the surface structure, which may complicate the assignment of the active phase. For this reason, we have applied 2D Planar Laser Induced Fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts [5-7]. In particular, these measurements enables a direct view of the onset and location of the catalytic activity. Further, the gas phase distribution during a catalytic reaction from more complicated samples, such as a curved single crystal upon ignition [8] may be explored, see Fig. 1. [1] S. Blomberg et al; Phys. Rev. Lett. 110, 117601 (2013). [2] J. Gustafson et al; Science, 343, 758 (2014). [3] S. Matera and K. Reuter, Phys. Rev. B 82, (2010) 085446. [4] S. Matera et al; ACS Catalysis 5, 4514 (2015). [5] J. Zetterberg et al; Rev.Sci. Instrum. 83, 053104 (2012). [6] J. Zetterberg et al; Nat. Comm. 6, 7076 (2015). [7] S. Blomberg et al; ACS catalysis 5, 2028 (2015). [8] S. Blomberg et al; ACS Catalysis 7, 110 (2016).

  9. Chemistry Department Seminar

    "Methane reforming with CO2 over Ni-Co/CeZrO2 catalysts"

    Presented by Dr. Petar Djinovic, Department for Environmental Sciences and Engineering, Slovenia

    Tuesday, November 28, 2017, 11 am
    Chemistry Bldg, 555, Room 300

    Hosted by: Dr. Jose Rodriguez

    Methane reforming with CO2 presents a possible pathway for valorization of natural gas or biogas to syngas (H2 and CO). Transition metal catalysts suffer from fast deactivation, mainly due to carbon accumulation. This lecture will focus on systematic development of bimetallic NiCo catalysts dispersed over CeZrO2 supports with the final realized aim of enabling long-term stable operation in a wide range of feed compositions. The role of bimetallic cluster size and amount of labile oxygen species in the CeZrO2 support on preventing the carbon accumulation will be discussed. Catalytic tests with isotopically labeled 13CO2, enabled us to identify the contribution of each reactant to the accumulated carbon pool and to distinguish between their reactivity. By replacing lattice oxygen contained in NiCo/CeZrO2 catalysts with isotopically labelled 18O, we were able to monitor transient changes of the catalyst's behavior during methane dry reforming reaction and identify the destination of lattice oxygen in the reaction products.

  10. Chemistry Department Seminar

    "Ambient Pressure XPS as a Tool to Probe Metal-Oxide Catalyst Behaviour"

    Presented by David Grinter, Diamond Light Source Ltd, Diamond House, Harwell Science & Innovation Campus, Didcot, Oxfordshire

    Monday, November 13, 2017, 11 am
    Room 300 - Chemistry Bldg. 555

    Hosted by: Sanjaya Senanayake

    Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) has provided numerous important insights into the behaviour of materials under conditions out of reach of traditional surface science experiments. In the first part of this talk I will highlight the application of AP-XPS to a number of model heterogeneous catalyst systems based on TiO2 and CeO2. Catalysts composed of metal-oxide supported nanoparticles have wide ranging industrial uses with particular energy-related applications including alternative fuel synthesis. I will demonstrate how AP-XPS plays a vital role as part of a multi-technique approach into investigating the reactions that occur at the surface of such materials. Figure 1. Cartoon depiction of the interrogation of a model supported catalyst by AP-XPS, and C1s AP-XPS spectra from a Ni/CeO2 catalyst under methane dry reforming conditions. The second part of my talk will cover the development and recent science commissioning experiments at the newest beamline at Diamond Light Source (UK) – B07 VERSOX (Versatile Soft X-ray). The VERSOX beamline is designed to provide synchrotron radiation soft X-rays between 50 and 2800 eV for studying atomic structures and the electronic/chemical properties of surfaces and interfaces by Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Spectroscopy (NEXAFS) under wide-ranging pressures (10-10 to 1000 mbar) and temperatures (100-1200 K). The beamline is designed to have separate sources and optical components that will allow independent and parallel operation of two soft X-ray branch lines; B07-C (Ambient Pressure) and B07-B (High Throughput). Figure 2. Beamline layout of B07 VERSOX, and C K-edge XAS spectra from a diamond (001) surface

  11. Chemistry Department Colloquium

    "Can Coherence Enhance Function in Chemical and Biophysical Systems?"

    Presented by Professor Gregory D. Scholes, Dept. of Chemistry, Princeton University

    Monday, September 25, 2017, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Matt Bird

    Coherence phenomena arise from interference, or the addition, of wave-like amplitudes in phase. While coherence has been shown to yield transformative new ways for improving function, advances have been limited to pristine matter, as quantum coherence is considered fragile. Recent evidence of coherence in chemical and biological systems, however, concludes that the phenomena is robust and can survive in the face of disorder and noise. I will present the state of recent discoveries. For example, two-dimensional electronic spectroscopy data allow quantitative analysis of vibronic coherence in the photosynthetic light harvesting complexes [1]. I will show how vibronic coherence plays a special role in downhill energy transfer, increasing energy transfer rates remarkably—even when electronic coupling is weak [2]. I will discuss how coherence might be found in electron transfer reactions. I will conclude with a forecast for the role of function as a design element in realizing coherence [3]. [1] Scholes, et al. "Lessons from nature about solar light harvesting" Nature Chem. 3, 763–774 (2011). [2] Dean et al. "Vibronic Enhancement of Algae Light Harvesting" Chem (Cell Press) 1, 858–872 (2016). [3] Scholes, et al. "Optimal Coherence in Chemical and Biophysical Dynamics" Nature 543, 647–656 (2017).

  12. Chemistry Department Colloquium

    ""Taking Snapshots of Reaction Intermediates in Metalloenzymes and Catalysts with X-ray Techniques""

    Presented by Junko Tano, Ph.D., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory

    Monday, September 11, 2017, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Javier Concepcion

    Our group is interested in the mechanisms of the catalytic reactions in both natural and inorganic systems. Using various X-ray techniques as tools, we are studying how the catalysts modulate and control multielectron reactions by following the reaction under functional conditions. We have developed spectroscopy and diffraction techniques necessary to fully utilize the capability of the XFELs for a wide variety of metalloenzymes, and to study their chemistry under functional conditions. One of such methods is simultaneous data collection for X-ray crystallography and X-ray spectroscopy, to determine the overall structural changes of proteins and the chemical changes at metal catalytic sites. In parallel to the detection techniques, we have developed an efficient sample delivery method that involves deposition of droplets on a conveyor belt. This 'Droplet on Tape' (DOT) method, delivers a single drop of the crystal suspension or solution sample onto a tape, which then can be transported to the X ray intersection point with a variable delay in time. In the process, the sample is photochemically or chemically activated at various time delays to capture reaction intermediates with crystallography and spectroscopy. In the field of inorganic catalysts, improved catalysts for electroreduction of carbon dioxide are highly important for promoting the generation of carbon-based reduction products. To gain a fundamental understanding needed to tailor novel catalysts, in particular for the selectivity of the products, the information of the early steps of the electroreduction process on catalyst surfaces is important. We have optimized and utilized surface-sensitive soft and hard X-ray techniques, including grazing incident X-ray absorption spectroscopy, X-ray diffraction, and ambient pressure X-ray photoemission spectroscopy to investigate the interaction of metal catalytic surfaces with electrolytes and/or gases (CO2 and/or H2O) under in situ/operando conditions.

  13. Chemistry Department Colloquium

    "Chemical Kinetics and Tunneling on Interstellar Dust Grains"

    Presented by Professor Gunnar Nyman, Dept. of Chemistry and Molecular Biology, University of Gothenburg, Goteborg, Sweden, Sweden

    Monday, August 28, 2017, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Greg Hall

    Dust can be important for the interstellar chemistry in the gas phase. The process where an atom or molecule lands on a dust grain, diffuses on the grain and meets another atom or molecule to form a new species, which can then desorb from the grain is essentially a description of how heterogeneous catalysis occurs. The importance of this process would depend on the diffusion rate of at least one of the adsorbed species and the products desorbing from the grain. This is particularly relevant for H2 formation in interstellar space. Atoms and molecules adsorbed on grains may be modeled as sitting in a local potential energy minimum. Diffusion can then be thought of as occurring through consecutive jumps from one minimum to another. The transition rate constants between adjacent minima can be estimated by for instance transition state theory. Such rate constants can in turn be used in Kinetic Monte Carlo simulation to obtain diffusion rates. Light atoms, particularly hydrogen atoms can tunnel through potential energy barriers. Tunneling may therefore substantially increase the rate of transition from one minimum to the next and thus the diffusion rate. Deuterium tunnels less efficiently than the lighter isotope and kinetic isotope effects (KIEs) are thus expected. Laboratory experiments have been carried out where either H atoms or D atoms diffuse on amorphous or polycrystalline ice at 10 K. Interesting KIEs were obtained.

  14. Nuclear Theory/RIKEN Seminar

    "Better fitting through (fictitious) chemistry"

    Presented by Pasi Huovinen, Uniwersytet Wroclawski

    Monday, June 19, 2017, 10 am
    Small Seminar Room, Bldg. 510

    Hosted by: Heikki Mantysaari

    One of the puzzles we have faced at the LHC is why the thermal models apparently cannot properly fit the yield of protons. I will explore how the fit improves if we assume that nucleon-antinucleon annihilations freeze-out way later than all other number changing processes or if strange particles freeze-out before non-strange particles, and how this affects the final particle distributions in hydrodynamical calculations.

  15. Chemistry Department Seminar

    "Modeling of the synergistic behavior of adjacent Pt{111}"

    Presented by Thobani Gambu, Catalysis Institute, Department of Chemical Engineering,, South Africa

    Wednesday, June 14, 2017, 4 pm
    Room 300 - Chemistry Bldg. 555

    Hosted by: Miomir Vukmirovic

    Abstract The oxygen reduction reaction (ORR) is particularly interesting, especially in the context of fuel cells and metal-air batteries [1,2]. The loss in cell potential at low current densities accounts for over 67% of the total potential loss and is primarily attributed to slow ORR kinetics [3]. When modelling the overall ORR activity over multifaceted Pt nanocrystallites, it is generally assumed that the different surface regions, i.e. terraces, edges and corners, are kinetically isolated and can therefore be modelled independently [4-5]. A range of ORR mechanisms have been proposed and the corresponding energetics, i.e. reaction and activation energies, have been calculated and reported [6-8]. A closer look at the reaction mechanisms and energetics shows that (1) O and OH removal over a Pt(111) and Pt(100) surface, respectively, is the most energetically hindered step, [6-8] and (2) facilitating an OH/O exchange between the Pt{111} and Pt{100} facets may result in improved ORR specific activity. Therefore, this study investigates the extent of O and OH cross-surface diffusion between the Pt{111} and Pt{100} facets of a pure Pt nanorod model. Furthermore, the cross-surface diffusion of OH on modified Pt nanorod models is reported. References 1. Gewirth, A. A. and Thorum, M. S. Inorg. Chem. 49, 3557 (2010). 2. Nie, Y., Li, L. and Wei, Z. Chem. Soc. Rev. 44, 2168 (2015). 3. Gasteiger, H. A., Kocha, S. S. et al. Appl. Catal. B Environ. 56, 9 (2005). 4. Tripkovic, V., Cerri, I. et al. Catal. Letters. 144, 380 (2014). 5. Nesselberger, M., Ashton, S. et al. J. Am. Chem. Soc. 133, 17428 (2011). 6. Li, K., Li, Y. et al. J. Mater. Chem. A. 3, 11444 (2015). 7. Duan, Z. and Wang, G. J. Phys. Chem. C. 117, 6284 (2013). 8. Ford, D. C., Nilekar, A. U. et al. Surf. Sci. 604, 1565 (2010).

  16. CFN Colloquium

    "Materials Chemistry via Electrochemistry: Electrochemical Synthesis of Semiconductor Electrodes and Catalysts for Use in Solar Energy Conversion"

    Presented by Kyoung-Shin Choi, Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53796

    Thursday, June 1, 2017, 4 pm
    CFN, Bldg 735, 2nd Floor Seminar Room

    Hosted by: Mingzhao Lu

    Harvesting energy directly from sunlight as nature accomplishes through photosynthesis is a very attractive and desirable way to solve the energy challenge. Many efforts have been made to find appropriate materials and systems that can utilize solar energy to produce chemical fuels. One of the most viable options is the construction of a photoelectrochemical cell that can directly utilize solar energy to drive chemical reactions (e.g. reduction of water to H2, reduction of CO2 to carbon-based molecules). For successful construction of photoelectrochemical cells, simultaneous developments of photoelectrodes, which will efficiently capture photons to generate and separate electron-hole pairs, and catalysts, which will facilitate the use of photogenerated electrons and holes for desired interfacial charge transfer reactions, are necessary. Furthermore, optimally interfacing photoelectrodes and catalysts is critical because the photoelectrode/catalyst interface can govern the overall efficiency of the integrated photoelectrode system. Our research group has been developing new electrochemical synthesis conditions to produce semiconductor electrodes and catalysts with precisely controlled compositions and architectures. In this seminar, we will discuss synthesis and properties of a few promising photoelectrode and catalyst systems for use in solar energy conversion. New synthesis strategies to improve photon absorption, charge transport properties, and catalytic properties will be presented. We will also discuss various strategies to increase the overall utility and efficiency of the photoelectrochemical cells, which include our new results on electrochemical and photoelectrochemical biomass conversion.

  17. Chemistry Department Colloquium

    "Adsorption and oxidation reactions on RuO2 and IrO2 surfaces"

    Presented by Jason F. Weaver, University of Florida, Dept. of Chemical Engineering

    Tuesday, May 30, 2017, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Sanjaya Senanayake

    Interest in the surface chemistry of late transition-metal oxides has been stimulated by observations that the formation of metal oxide layers tends to dramatically alter the catalytic performance of transition metals in applications of oxidation catalysis. In this talk, I will discuss our recent investigations of the growth and chemical properties of rutile RuO2 and IrO2 surfaces. Our interest in these oxides derives mainly from computational predictions that CH4 binds strongly and should undergo C-H bond activation at low temperature on certain facets of IrO2. I will discuss our investigations of the oxidation of metallic Ir surfaces by O-atom beams as well as O2 at pressures above 1 Torr. We find that stoichiometrically-terminated IrO2(110) layers could only be formed by oxidizing Ir(111) and Ir(100) at sufficiently high temperature and O2 pressure. I will discuss the binding characteristics of small molecules, and our recent discovery of highly facile CH4 activation on the IrO2(110) surface at temperatures as low as 150 K. We show that CH4 activation occurs by a mechanism wherein a molecularly-adsorbed ?-complex serves as the precursor for CH4 dissociation on the IrO2(110) surface and that the barrier for C-H bond cleavage is nearly 10 kJ/mol less than the molecular binding energy. Lastly, I will discuss results showing how the partial replacement of surface O-atoms with Cl-atoms alters the oxidation chemistry of methanol on RuO2(110), and may provide an approach for modifying the selectivity of RuO2 and IrO2 surfaces for other oxidation chemistries.

  18. Chemistry Department Colloquium

    "Electrocatalysts for Oxygen Reduction Reaction"

    Presented by Minhua Shao, The Hong Kong University of Science and Technology, Department of Chemical and Biomolecular Engineering, Hong Kong

    Friday, May 26, 2017, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Alex Harris

    Low temperature fuel cells are electrochemical devices that convert chemical energy directly to electricity. They have great potential for both stationary and transportation applications and are expected to help address the energy and environmental problems that have become prevalent in our society. Despite their great promise, commercialization has been hindered by lower than predicted efficiencies and high loading of Pt-based electrocatalysts in the electrodes. For more than five decades, extensive work has being focused on the development of novel electrocatalysts for fuel cell reactions. In this talk, I will present recent progress in developing advanced electrocatalysts mainly for oxygen reduction reaction in my group, with an emphasis on core-shell and shape controlled nanocrystals. Fuel cell testing results on these advanced catalysts will be shared. The mechanisms for activity enhancement will also be discussed based on the results of density functional theory calculations.

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