Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

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Model Catalysis by Size-Selected Cluster Deposition PI: Scott L. Anderson Chemistry Department, University of Utah 315 S. 1400 E. Rm 2020 Salt Lake City, UT 84112 anderson@chem.utah.edu Program Scope The goal of our research is to explore correlations between supported cluster size, electronic and morphological structure, the distributions of reactant binding sites, and catalytic activity, for model catalysts prepared using size-selected metal cluster deposition. The work to date has focused on catalysts with catalytically active metal clusters deposited on metal oxide supports, and on electrocatalysis by metal clusters on glassy carbon electrodes. We are also looking at effects of cluster size on Pd-catalyzed H2 splitting and uptake in metals. The experimental setup is quite flexible. The main instrument has a mass-selecting ion deposition beamline fed by a laser vaporization source that produces high fluxes at low deposition energies (~10 9 Pd10/sec in a 2 mm diameter spot at 1 eV/atom, for example). Typical samples with 0.1 ML-equivalent of metal, deposited in the form of Mn + can be prepared in 10 – 20 minutes, and our analysis methods are also quite fast. Speed is important, because even in UHV these samples are highly efficient at collecting adventitious contaminants, due to substrate-mediated adsorption. Sample morphology is probed by low energy He + ion scattering (ISS), electronic structure is probed by x-ray and UV photoelectron spectroscopy and ion neutralization spectroscopy (XPS, UPS, INS), and reactivity is studied using a differentially pumped mass spectrometer surrounded by a cluster of pulsed and cw gas inlets that can be used to dose the sample while various temperature programs are executed. The main UHV analysis chamber has a port in the bottom, equipped with a gate valve, a triple differential seal, and one of several interchangeable small chambers with their own pumping systems. When the sample is positioned in the lower chamber is it isolated from the main UHV system, enabling high pressures procedures such as film growth or in situ electrochemical studies. Recent Progress Strong Effects of Cluster Size and Air Exposure on Platinum Electrocatalysis We studied the O2 reduction reaction (ORR) in 0.1 M HClO4, catalyzed by Ptn (n ≤ 11) deposited on glassy carbon electrodes (GCEs). Very strong effects of cluster size and air exposure were observed, with all clusters except Pt7 showing high activity for carbon oxidation by water when studied in situ, without air exposure. Only Pt7 showed the expected ORR activity. If the same size clusters were deposited on GCEs in vacuum, but exposed briefly to laboratory air before electrochemistry, then the high carbon oxidation activity was Fig. 1: Pt7/GCE: CVs in nitrogen- and oxygen-saturated 0.1M HClO4 at a sweep rate of 0.1 Vs -1 , starting at 1.3 V (indicated by dot), and scanning to - 0.1 V vs. Ag/AgCl and back. 5
entirely quenched, presumably due to reaction of the highly active Ptn with species in the air. For Pt7, air exposure leads to quenching of ORR activity, replaced by reversible redox of adventitious organic species. The instrument was modified to allow in situ electrochemical studies to be made in the lower chamber. A retractable electrochemical cell was constructed of PEEK, consisting of a 4 mm diameter working section that contains a Pt counter electrode (working cell volume ≈ 15 μL). One end of the working section is open, with a lip holding a 3 mm diameter O-ring that is used to seal the cell against the surface of the GCE. The other end of the working section is sealed to a reference electrode section, communicating via a fritted Vycor disk. The reference electrode was Ag/AgCl. Both working and reference sections of the cell are equipped with Teflon tubes used for injecting electrolyte, and ports to allow electrolyte solution to flow out of the cell. Electrolyte flows are controlled by a syringe pump located outside the vacuum system. To allow in situ electrochemical measurements, an electrode is first prepared by depositing Ptn on a clean, degassed GCE in UHV, which is then lowered through the triple seal into the lower chamber while the electrochemical cell is retracted. The electrochemical cell is then pushed against the surface of the GCE, sealing via the O-ring at the open end of the working section. For in situ experiments, the lower chamber was vented with high purity Ar, then the working and reference sections were filled with 0.1 M HClO4, and 3 M NaCl, respectively. Cyclic voltammograms (CVs) were acquired using a CH Instruments model 600D potentiostat. The ORR results for Pt7/GCE are show in Fig. 1, in the form of CVs taken in both N2- and O2-saturated HClO4. The structure of the CV is similar to that seen both in our in situ cell and in the literature for Pt nanoparticles on GCE, and the activity per Pt atom is roughly twice that of Pt nanoparticles, probably because the small clusters have essentially all the Pt on the surface, and are highly dispersed on the GCE. Optical microscopy of the electrode after several hundred CV cycles showed no signs of any degradation. Fig. 2 shows CVs for Pt4/GCE, and also a post-electrochemistry optical micrograph of Fig. 2: Top. CV of Pt4/GCE in N2- and O2-saturated 0.1M HClO4 at a scan rate of 1 Vs -1 from 0.4 to -0.1 V vs. Ag/AgCl and back. Bottom. Optical micrograph of the electrode after electrochemical cycling. Fig. 3 XPS of as-deposited Ptn/GCE in UHV 6
Page 1 and 2: Eighth Condensed Phase and Interfac
Page 3 and 4: Potential energy landscape of the (
Page 5 and 6: Agenda
Page 7 and 8: Session III Chair: Jay A. LaVerne,
Page 9 and 10: Table of Contents
Page 11 and 12: Transition Metal-Molecular Interact
Page 13 and 14: Ultrafast Electron Transport across
Page 15 and 16: CPIMS Principal Investigator Abstra
Page 17 and 18: VUV LDPI image of a polymer photore
Page 19: Publications based on DOE support (
Page 23 and 24: Future Plans In addition to the TiO
Page 25 and 26: The relative path indexes of the ur
Page 27 and 28: We have recently carried out molecu
Page 29 and 30: have been obtained with γ-rays sug
Page 31 and 32: Two novel plasma devices have been
Page 33 and 34: (Figure 2) can be adsorbed exclusiv
Page 35 and 36: 3. Future Plans Our planned work de
Page 37 and 38: Figure 1: Snap shots from molecular
Page 39 and 40: 6. Varilly, P., A. J. Patel and D.
Page 41 and 42: hypothesis that delocalized charges
Page 43 and 44: Efforts will be made to observe ele
Page 45 and 46: Photochemistry and Solvation Dynami
Page 47 and 48: complementary to work we have carri
Page 49 and 50: The Co3O4 films for the optical pum
Page 51 and 52: chamber will allow us to heat the s
Page 53 and 54: calculations. Additional PMF calcul
Page 55 and 56: the gas solute first needs to cross
Page 57 and 58: laser system, which is an infrared
Page 59 and 60: Publications (10/1/2009-present) fo
Page 61 and 62: interest are: (i) What is the diffu
Page 63 and 64: and anilino groups attached to the
Page 65 and 66: had been formed. This coincides wit
Page 67 and 68: Figure 1. (A) Simplified bR photocy
Page 69 and 70: Figure 4. Photocurrent density of b
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single-file diffusion and cannot ca
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PUBLICATIONS SUPPORTED BY USDOE CHE
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arrangement. However, the hydrogen
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(5) “Water Dynamics in Salt Solut
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from high- energy x-ray diffraction
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concentrated aqueous solutions. The
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molecule’s center of mass, or alt
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Moreover, SHG studies by Saykally
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The effective fragment potential (E
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10. D.D. Kemp, J. Rintelman, M.S. G
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temperature dependent, equilibrium
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mimicking real organic photovoltaic
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100 kHz amplifier, SE-FSRS was succ
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photovoltaics will be explored via
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for laser surface reactions to thes
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This is a significant advantage of
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the STM, which might underlie the u
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Future Plans: Figure 3. One and two
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methane molecule and a lattice atom
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eactive than the Ni, experiment sug
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Fig. 1. PE spectra of M3Oy � (M =
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each of the intermediates obtained
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a regime where each solvent molecul
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observables that arise from subtle
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total potentials. One can see from
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Our calculations have shown that ch
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our understanding of structure and
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viscosity, η, are inversely relate
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photodissociation of the metal - NO
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from a Ru 2p3/2 orbital to an orbit
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Integrated O 2 PSD (ML) Integrated
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anisotropy in the structure of the
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XPS studies have been performed on
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Publications with BES support since
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MLCT (metal to ligand charge transf
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molecule-metal interface without a
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observe the predicted effects, whic
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(4*) Lymar, S. V.; Schwarz, H. A. J
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(τ .820 ns), but we have not been
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B. Photodissociation spectroscopy o
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oth BLYP and PBE. Our results have
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Publications from BES support (2010
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understanding of factors that contr
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Our talk will discussion our initia
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Figure 1 shows the band structure o
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likely to also occur in low coordin
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These results are promising indicat
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This page is intentionally left bla
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method recently developed by Prende
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and coordination regions. A differe
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two ions I - [3] and IO3 - [7]. One
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"Probing the Hydration Structure of
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world-wide scientific user base sup
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10) C. Zhang, M.E. Grass, A.H. McDa
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produce the nanoparticles needed fo
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step as a symmetry-breaking templat
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work provides what we believe in th
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Selected publications acknowledging
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2. Optical Stark study of PtF (Acce
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Figure 4. The Q(3.5) line of the [1
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In marked contrast to the selective
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y depositing cobalt onto copper sin
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Carlo calculations, we have carried
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approach on a model phenol-amine pr
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We performed pump-probe experiments
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15. “A phenomenological approach
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may be initially produced in a non-
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4. Inelastic scattering of hydrogen
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Using QM/MM free energy methods we
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gas phase using electrospray ioniza
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order of Li + > Na + > K + for comp
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2. MM Meyer, XB Wang, CA Reed, LS W
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Technical Approach and Progress to
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Ionic liquid synthesis and characte
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Studies of structure and reaction d
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structure theory that include elect
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9. S. Pandelov, J. C. Werhahn, B. M
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pulse duration is a few times longe
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Figure 1 (Left) The HOMO and LUMO e
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slightly preferable in energy, the
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Participant List Dr. Musahid Ahmed
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Professor Kenneth Eisenthal Columbi
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Dr. Ireneusz Janik Notre Dame Radia
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Professor Eric Potma University of
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Dr. James Wishart Brookhaven Nation
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Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

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