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July 2018
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  1. Chemistry Department Colloquium

    11 am, Hamilton Seminar Room, Bldg. 555

    Hosted by: Sanjaya Senanayake

    The addition of carbon and nitrogen to early transition metals like molybdenum and vanadium can result in materials with properties that are similar to those of platinum group metals (PGMs). In the mid-1970s, for example, it was discovered that tungsten carbides can catalyze hydrogenation reactions that previously were only known for PGMs, and more recently we observed that molybdenum nitrides are capable of bulk hydrogen storage like Pd. Since then, early transition metal carbides and nitrides have been investigated for a variety of reactions. This paper will describe our work to design and synthesize nanostructured early transition metal carbides and nitrides for reactions including selective hydrogenations. Our research has focused on understanding the genesis of the materials, unraveling the reaction mechanisms and determining structure-function relationships that will enable the rational design of these materials. Of particular interest are CO2 hydrogenation and ammonia synthesis, reactions for which new catalysts are needed to reduce energy consumption.

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  1. JUL

    23

    Monday

    Chemistry Department Seminar

    11 am, Room 300, 3rd Flr. Chemistry Bldg. 555

    Monday, July 23, 2018, 11:00 am

    Hosted by: Xiao-Qing Yang

    Phase transformation of layered structure into spinel structure has been detrimental for most of layered oxide cathodes. Even if a lot of efforts have been made to relieve this highly irreversible phase transformation, there have been few successful results. However, we firstly observed the possibility to make this irreversible phase transformation extremely reversible by utilizing Na- birnessite (NaxMnO2•yH2O; Na-bir) as a basic structural unit, which has distinctive layered structure containing crystal water. Herein, the crystal water in the structure contributes to generating metastable spinel-like phase, which is the key factor for making this unusual reversibility happen. The reversible structural rearrangement between layered and spinel-like phases during electrochemical reaction could activate new cation sites and enhance ion diffusion with higher structural stability. This unprecedented reversible phase transformation between spinel and layered structure was deeply analyzed via combined ex situ soft and hard X-ray absorption spectroscopy (XAS) analysis with in situ X-ray diffraction (XRD). Fundamental mechanism on this reversible phase transformation was theoretically elucidated and confirmed by kinetic investigation using first-principle calculation. These results provide deep insight into novel class of intercalating materials which can deal with highly reversible framework changes, and thus it can pave an innovative way for the development of cathode materials for next- generation rechargeable batteries.

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  1. JUL

    23

    Monday

    Chemistry Department Seminar

    "Triggered Reversible Phase Transformation between Layered and Spinel Structure via Intercalated Hetero Species in Sodium Birnessite"

    Presented by Yong-Mook Kang, Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul, 04620, Republic of Korea., Korea, Republic of (South)

    11 am, Room 300, 3rd Flr. Chemistry Bldg. 555

    Monday, July 23, 2018, 11:00 am

    Hosted by: Xiao-Qing Yang

    Phase transformation of layered structure into spinel structure has been detrimental for most of layered oxide cathodes. Even if a lot of efforts have been made to relieve this highly irreversible phase transformation, there have been few successful results. However, we firstly observed the possibility to make this irreversible phase transformation extremely reversible by utilizing Na- birnessite (NaxMnO2•yH2O; Na-bir) as a basic structural unit, which has distinctive layered structure containing crystal water. Herein, the crystal water in the structure contributes to generating metastable spinel-like phase, which is the key factor for making this unusual reversibility happen. The reversible structural rearrangement between layered and spinel-like phases during electrochemical reaction could activate new cation sites and enhance ion diffusion with higher structural stability. This unprecedented reversible phase transformation between spinel and layered structure was deeply analyzed via combined ex situ soft and hard X-ray absorption spectroscopy (XAS) analysis with in situ X-ray diffraction (XRD). Fundamental mechanism on this reversible phase transformation was theoretically elucidated and confirmed by kinetic investigation using first-principle calculation. These results provide deep insight into novel class of intercalating materials which can deal with highly reversible framework changes, and thus it can pave an innovative way for the development of cathode materials for next- generation rechargeable batteries.

  2. AUG

    6

    Monday

    Chemistry Department Seminar

    "Synthesis of Fuels and Chemicals by Electroreduction over Copper Catalysts"

    Presented by Elizabeth J. Biddinger, The City College of New York, CUNY

    11 am, Room 300 - 3rd Flr. Chemistry Bldg. 555

    Monday, August 6, 2018, 11:00 am

    Hosted by: Sanjaya Senanayake

    Electrochemical synthesis methods offer opportunities to perform reactions under benign reaction conditions (at or near room temperature and pressure), use less harmful or waste-generating reaction steps, and perform selective reactions. In electroreduction reactions, externally-supplied hydrogen that is generally needed for reduction is not required. Rather, electrons, frequently paired with the electrolyte, are the reducing agents. New opportunities for utilization of electrochemical reactions exist with the emerging renewable electricity generation market. Due to the intermittent supply sources for many renewable electricity systems, excess electricity gets generated when peak generation (sunny or windy periods) does not match with demand. Electrochemical reactions can be performed at relatively low costs with this excess electricity to synthesize fuels for later use or chemicals. The work presented here will illustrate two synthesis systems via electroreduction – carbon dioxide electroreduction to hydrocarbons and furfural (a biomass-derived species) electrochemical hydrogenation and hydrogenolysis (ECH) to fuels and chemicals. Both of these reactions are performed over copper electrodes, serving as the catalysts for the system. Copper is utilized because of its unique balance between being active for the electroreduction and less active for the undesired side reaction hydrogen evolution. In CO2 electroreduction, copper is the only known metal to produce significant quantities of hydrocarbons. By tuning the morphology, the selectivity between ethylene and methane can be tuned. The results of morphological differences and the dynamic nature of copper surfaces will be discussed in terms of electrodeposition and the resulting CO2 electroreduction performance. In furfural ECH, both 2-methyl furan and furfuryl alcohol can be formed, while over many other metals 2-methyl furan is not formed. The reaction conditions for furfural ECH si

  1. Chemistry Department Colloquium

    "Turning Base Metals into Precious Metals: Nanostructured Early Transition Metal Carbides and Nitrides"

    Presented by Levi Thompson, University of Michigan, Department of Chemical Engineering,

    Monday, July 9, 2018, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Sanjaya Senanayake

    The addition of carbon and nitrogen to early transition metals like molybdenum and vanadium can result in materials with properties that are similar to those of platinum group metals (PGMs). In the mid-1970s, for example, it was discovered that tungsten carbides can catalyze hydrogenation reactions that previously were only known for PGMs, and more recently we observed that molybdenum nitrides are capable of bulk hydrogen storage like Pd. Since then, early transition metal carbides and nitrides have been investigated for a variety of reactions. This paper will describe our work to design and synthesize nanostructured early transition metal carbides and nitrides for reactions including selective hydrogenations. Our research has focused on understanding the genesis of the materials, unraveling the reaction mechanisms and determining structure-function relationships that will enable the rational design of these materials. Of particular interest are CO2 hydrogenation and ammonia synthesis, reactions for which new catalysts are needed to reduce energy consumption.

  2. Chemistry Department Seminar

    "Nanowires Devices for Emerging Energy Storage"

    Presented by Liqiang Mai, Wuhan University of Technology, China

    Friday, June 15, 2018, 11 am
    Room 300 - Third Floor - Chemistry Bldg. 555

    Hosted by: Xiao-Qing Yang

    One-dimensional nanomaterials can offer large surface area, facile strain relaxation upon cycling and efficient electron transport pathway to achieve high electrochemical performance. Hence, nanowires have attracted increasing interest in energy related fields. We designed the single nanowire electrochemical device for in situ probing the direct relationship between electrical transport, structure, and electrochemical properties of the single nanowire electrode to understand intrinsic reason of capacity fading. The results show that during the electrochemical reaction, conductivity of the nanowire electrode decreased, which limits the cycle life of the devices. We have developed a facile and high-yield strategy for the oriented formation of CNTs from metal−organic frameworks (MOFs). The appropriate graphitic N doping and the confined metal nanoparticles in CNTs both increase the densities of states near the Fermi level and reduce the work function, hence efficiently enhancing its oxygen reduction activity. Then, we fabricated a field-tuned hydrogen evolution reaction (HER) device with an individual MoS2 nanosheet to explore the impact of field effect on catalysis. In addition, we demonstrated the critical role of structural H2O on Zn2+ intercalation into bilayer V2O5·nH2O. The results suggest that the H2O-solvated Zn2+ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V2O5 framework, effectively promoting its diffusion. We also identified the exciting electrochemical properties (including high electric conductivity, small volume change and self-preserving effect) and superior sodium storage performance of alkaline earth metal vanadates through preparing CaV4O9 nanowires. Our work presented here can inspire new thought in constructing novel one-dimensional structures and accelerate the development of energy storage applications.

  3. Chemistry Department Seminar

    "Astrochemistry in the Laboratory – Combining Theory and Experiment"

    Presented by Kelvin Lee, Harvard-Smithsonian Center for Astrophysics

    Monday, June 11, 2018, 11 am
    Room 300, 3rd Floor, Chemistry Bldg. 555

    Hosted by: Greg Hall

    Brief overview of the laboratory and theoretical efforts in astrochemistry at the Harvard Smithsonian Center for Astrophysics. Will highlight one of our areas of research – the characterization and spectroscopy of molecular isomers in space by showcasing two recent projects (1) the rotational spectroscopy of ethynethiol (HCCSH), a higher energy isomer of thioketene, and (2) the first-principles high accuracy chemical network we are developing for the production and destruction of hydrogen (iso)cyanide in space.

  4. Chemistry Department Colloquium

    "Discovering Emergent Phenomena in Catalysis Through Large Scale Ab Initio Molecular Dynamics Simulations"

    Presented by Roger Rousseau, Pacific Northwest National Laboratory

    Tuesday, May 29, 2018, 11 am
    Hamilton Seminar Room, Bldg. 555

    Hosted by: Sanjaya Senanayake

    The current state of the art of electronic structure methods allows us to tackle model systems on the order of 100s to 1000s of atoms with suitable speed and efficiency to perform statistical mechanical sampling on millions of configurations. This has opened the door to using theoretical tools such as ab initio molecular dynamics (AIMD) combined with enhanced sampling techniques) to discover novel emergent phenomena that result from chemical complexity. Nowhere is this more needed than in catalysis, where models need to include support materials, the catalysts, the reactants and products all at elevated temperature and pressures. In this context, both global and local anharmonicities on the potential energy surface can lead to unexpected phenomena that can be discovered through large scale simulation yet are often not accounted for in current theoretical studies. This will be illustrated with examples drawn from the chemistry of metal particles on reducible supports [1-3], Brønsted acid chemistry in confined spaces [4] and reactivity at solid-liquid interfaces [5,6]. In the context of metal particles supported on reducible metal oxides (such as TiO2, CeO2 and RuO2), we have found that there is a strong coupling between the redox state of the support and the redox properties of the nanoparticle [1,2] such that unique catalytic processes can occur including: Redox state dependent reaction energies [2,3]; Formation of transient single atoms, which are themselves catalytic [1,3]; For prototypical reactions such as CO oxidation, a complex mechanistic landscape where catalysis can occur by competing mechanisms involving both the nanoparticle and single atom sites at the same time. Similar methods have been used to investigate the confinement effect in zeolite [4] and understand the free energetics of acid catalysis in confined media. It is shown that due to the large anharmonic effects associated with molecules, such as ethanol, interacting with the walls of a s

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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).

  13. 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.

  14. 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

  15. 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).

  16. 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.

  17. 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.

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