Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J2: Focus Session: Surface Chemistry and Catalysis IV |
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Sponsoring Units: DCP Chair: Jason Weaver, University of Florida Room: 102 |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J2.00001: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J2.00002: Benzene and Its Derivatives Adsorbed on Metal Surfaces: A Bag Full of Surprises Wei Liu, Matthias Scheffler, Alexandre Tkatchenko The study of molecule/metal interfaces is important for fundamental and applied surface science, and the electronic properties of these interfaces can be tuned by controlling their geometries. In this regard, a particular challenge for electronic structure theory is to reliably model the structure and stability of such hybrid interfaces. Here, we demonstrate that our DFT+vdW$\rm^ {surf}$ method [1] is able to describe 25 systems [\textit{e.g.}, benzene on Au(111) and Pt(111), thiophene/Ag(111), and DIP/Ag(111)] with an accuracy of 0.1~{\AA} in adsorption heights and 0.1~eV in binding energies wrt. reliable experimental data. In addition, our DFT+vdW$\rm ^ {surf}$ calculations lead to a few peculiar findings: (1) The vdW energy can contribute more to the binding of covalently bonded systems than it does in physisorbed interfaces [2,3]; (2) the binding energies of similar molecules can be identical, despite significantly different adsorption heights; (3) the physically bound (precursor) state for aromatics on Pt(111) can be prominently stabilized and long-lived, making it potentially useful in molecular switches [4]. [1] Ruiz, \textit{et al.}, PRL (2012). [2] Liu, \textit{et al.}, PRB (2012). [3] Liu, \textit{et al.}, NJP (2013). [4] Liu, \textit{et al.}, Nat. Commun. (2013). [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J2.00003: Selective self-assembly of molecular clusters with designed sizes on metal surfaces Jun Wang, Qing Li, Miguel Fuentes-Cabrera, Bobby G. Sumpter, Arthur P. Baddorf, Minghu Pan The self-assembly of ``magic'' molecular clusters on various substrates provides a new arena for studies of surface nanocatalysis and molecular electronics. Here we present the self-assembly of phenylacetylene molecules on Cu(100) by a combined low-temperature STM and in-depth density functional theory investigation. We observe the molecules form distinct tetramer clusters on Cu(100) at 40 K. Each cluster has a four-fold symmetry and consists of four molecules. A delicate balance of intramolecular and dipole-dipole interactions between clusters maintains this magic tetramer configuration on Cu(100). The strong interaction between the molecules and the copper surface creates an anchor at each adsorption site. Through comparison with our previous observed hexamer (six-molecule) clusters on Au(111), we conclude that the epitaxial relationship between the molecules and metal surfaces is crucial in defining magic numbers of surface-supported molecular clusters under weak intermolecular interaction. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J2.00004: One Step Propylene Epoxidation by Size Selected Subnanometer Cluster Silver Catalysts: Structure-Function Relationships Resolved Through in Situ Studies Eric Tyo, Bing Yang, Janae DeBartolo, Sonke Seifert, Stefan Vajda The selective partial oxidation of propylene at low temperatures is accomplished by soft-landed, size selected subnanometer Ag clusters. The activity and selectivity for the creation of propylene oxide vs. acrolein is found to be size and support dependent, determined through the temperature programmed reactivity (TPRx) investigation of three cluster sizes between 3 and 20 atoms and three supports (Al2O3, TiO2, and ZnO). in Situ synchrotron X-ray characterization including Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence X-ray Absorption Spectroscopy (GIXAS) were performed to determine structural morphology and oxidation state during catalytic activity. The oxidation state of the Agn clusters (GIXAS) varies significantly due to size and support. At higher temperatures, changes in size due to assembly are observed through GISAXS with marked dependence on support with aggregates presenting distinct chemical properties and activity. Utilizing the presented method of catalyst synthesis and in situ characterization, it is feasible to investigate single active sites without the convolution that occurs in many studies from a range of particles sizes and active sites being present. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J2.00005: Reaction-driven restructuring of Pt and Pd catalysts: In operando X-ray absorption spectroscopy study Annika Elsen, Ulrich Jung, Yuanyuan Li, Anatoly Frenkel, Ralph Nuzzo The catalyzed hydrogenation of ethylene on supported metal catalysts has been intensively investigated, mainly because this reaction lies at the heart of many industrial processes. Most previous studies have been performed using surface science techniques in UHV. Therefor little is known about the nature of the active state of the catalyst at ambient pressure where the kinetics is very different. We employed operando X-ray absorption spectroscopy (XAS) to correlate the structural changes of SiO$_{\mathrm{2}}$-supported Pt and Pd catalysts with their activity for ethylene hydrogenation. The XAS experiments were performed at the beamlines X19A and X18B, NSLS, BNL. For both catalysts, strong and largely reversible transformations of the metal bonding were identified at about the maximum ethane conversion. The changes were different for Pt/SiO$_{\mathrm{2}}$ and Pd/SiO$_{\mathrm{2}}$ due to the ability of the latter to form bulk hydride, while the former can only adsorb hydrogen on the surface. As a result, Pt/SiO$_{\mathrm{2}}$ undergoes disordering of the surface, leading to a strong reduction of the Pt-Pt coordination number under H$_{\mathrm{2}}$-deficient conditions, while the main effect for Pd/SiO$_{\mathrm{2}}$ is the hydrogen uptake with concomitant increase in Pd-Pd bond length. The correlation between these different kinds of order transitions and differences in rates for these catalysts will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J2.00006: In-situ observation of sintering of Mono-metallic nanoparticles Vineetha Mukundan, Shiyao Shan, Jin Luo, Chuan-Jian Zhong, Oana Malis Grain growth is detrimental in many applications of nanoparticles, especially for catalysis. During the physical processing of nanoparticles for various applications, they tend to coalesce and sinter. Upon grain growth, the size dependent physical and chemical properties of these nanoparticles undergo complete changes. For example, the nanoparticles need to be thermally activated to function as catalysts. However the thermal treatment renders these catalysts less efficient due to the decrease in electrochemically active area related to sintering. So it is imperative to study growth laws which predict the sizes of nanoparticles as a function of temperature to have better control of the structures and sizes in the nano-scale regime. The grain growth and sintering of Au, Pd and Cu nanoparticles of sizes 2-5nm were monitored using in-situ synchrotron based x-ray diffraction (XRD) in the temperature range from 500C to 800C. The data was compared to the empirical Kolmogorov-Johnson-Mehl-Avrami analysis and the activation energy was estimated. This was complemented with the study of transmission electron microscopy (TEM) data and mass transport analysis using basic sintering laws. The diffusion coefficients predicted from XRD and TEM were compared. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 4:18PM |
J2.00007: Exploration of surface chemistry and structure of catalysts under reaction condition and during catalysis with surface-sensitive in-situ techniques Invited Speaker: Franklin (Feng) Tao In heterogeneous catalysis, each catalytic event occurs on a catalytic site. The catalytic site typically consists of a couple of or a few atoms of a catalyst which pack into a structure to offer specific electronic state to turn on a catalytic reaction. Surface structure and chemistry are the key for understanding a catalytic mechanism. From thermodynamic point of view, the surface structure of a catalyst depends on the environment of reactant gases or liquid around the catalyst. Thus, the surface chemistry and structure of a catalyst under a reaction condition or during catalysis (in an environment of reactant(s) with certainly pressure) could be different from those from ex-situ studies. In-situ surface science characterization techniques have been developed for disclosing the hidden surface chemistry and structure of catalysts under reaction conditions or during catalysis. In-situ ambient pressure XPS (AP-XPS) and ambient pressure STM (AP-STM) are two of these surface-sensitive techniques appropriate for exploring surface chemistry and structure, respectively. In this talk, I will present the origin of pressure dependent surface chemistry and structure from thermodynamic point of view. AP-XPS and AP-STM techniques will be introduced briefly. I will focus on (1) the evolution of surface composition and oxidation state of a reducible oxide and how the evolution is correlated to the corresponding catalytic performances, (2) the distribution of surface elements on surface of a bimetallic catalyst under a reaction condition and how a restructuring is used to generate a new surface with different catalytic performance, and (3) geometric restructuring of a metal catalyst surface at atomic scale and how it is related to its catalytic performances. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J2.00008: Acid-Base Interaction Induced Stability of Self-assembled Monolayer at Solid Interface Characterized by Sum Frequency Generation Spectroscopy He Zhu, Ali Dhinojwala Long chain alcohols have been known to form hydrogen bonding with the hydroxyl groups on aluminum oxide surface. We used the interface sensitive technique, sum frequency generation (SFG) spectroscopy, to study the molecular structure of hexadecanol at liquid/sapphire interface and air/sapphire interface. We characterized the hydrocarbon chain conformation and the hydrogen bonding at different temperatures. Peak intensity changes were used to determine order-disorder transition of interfacial molecules. The transition hysteresis will also be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J2.00009: First principles calculations of enthalpy and O-H stretching frequency of hydrogen-bonded acid-base complexes Mesfin Tsige, Ram Bhatta, Ali Dhinojwala Understanding the acid-base interactions is important in surface science as it helps to rationalize materials properties such as wetting, adhesion and tribology. Quantitative relation between changes in enthalpy ($\Delta$H) and frequency shift ($\Delta\nu$) during the acid base interaction is particularly important. We investigate $\Delta$H and $\Delta\nu$ of twenty-five complexes of acids (methanol, ethanol, propanol, butanol and phenol) with bases (benzene, pyridine, DMSO, Et$_2$O and THF) in CCl$_4$ using intermolecular perturbation theory calculations. $\Delta$H and $\Delta\nu$ of complexes of all alcohols with bases except benzene fall in the range from -14 kJ/mol to -28 kJ/mol and 215 cm$^{-1}$ to 523 cm$^-1$, respectively. Smaller values of $\Delta$H (-2 to -6 kJ/mol) and $\Delta\nu$ (23 to 70 cm$^{-1}$) are estimated for benzene. For all the studied complexes, $\Delta$H varies linearly (R$^2$ ? 0.974) with $\Delta\nu$ yielding the average slope and intercept of 0.056 and 1.5, respectively. Linear correlations were found between theoretical and experimental values of $\Delta$H as well as $\Delta\nu$ and are concurrent with the Badger-Bauer rule. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J2.00010: Porous Particles: Controlling Molecular Diffusion within Metal-Organic Frameworks Ah-Young Jee, Melinda Sindoro, Steve Granick Systematic investigation of molecular diffusion under nanoconfinement is carried out utilizing pore tunability of ionic metal-organic frameworks (MOFs). The translational and rotational diffusion of specially-selected guest dyes is evaluated by fluorescence correlation microscopy (FCS). A curious novel technique is demonstrated of controlling diffusion by switching counterions. Systematically, this study provides generalizable examples of how pore size, guest size, and host-guest interaction affect diffusion within nanopores. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J2.00011: Manipulating the Band Structure of SrTiO$_{3}$ with Strain Darrell G. Schlom, Charles M. Brooks, Dagmar Chvostova, Vladimir Trepakov, Megan E. Holtz, Nik J. Podraza, Robert F. Berger, Lena F. Kourkoutis, Tassilo Heeg, Margitta Bernhagen, Reinhard Uecker, Juergen Schubert, Craig J. Fennie, Jeffrey B. Neaton, David A. Muller, Alexandr Dejneka SrTiO$_{3}$, the hydrogen atom of perovskites, is a very stable photocatalyst for water splitting. In this talk we demonstrate that the bandgap of SrTiO$_{3}$ can be altered by $\pm$ 10{\%} (0.3 eV) using biaxial strain in combination with phase transitions. The strain behavior is predicted and experimentally observed to be significantly different for (100) vs. (111) biaxially strained SrTiO$_{3}$ surfaces. In the absence of phase transitions the bandgap of biaxially strained SrTiO$_{3}$ decreases. In contrast, a strain-induced ferroelectric phase transition results in an increase in the bandgap. The band structure can also be morphed from indirect to direct bandgap through an antiferrodistortive phase transition. Both of these phase transitions can be manipulated using experimentally realizable biaxial strains, providing a new means to accomplish bandgap engineering of SrTiO$_{3}$ and related perovskites. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J2.00012: Halide anion dependence of ionic surfactant adsorption in air/water interface Doseok Kim, Wenjie Wang, Woongmo Sung, Mingqi Ao, David Vaknin It was recently proposed that there is surface excess of halide anions at the air/water interface, and more surface excess of I$^{\mathrm{-}}$ than Br$^{\mathrm{-}}$ or Cl$^{\mathrm{-}}$, which cannot be explained by Debye-Huckel theory. In case of charged surfaces such as Gibbs monolayer consisting of cationic surfactant molecules, surface excess of anions can also be expected. In this study, by using surface-sensitive grazing angle X-ray fluorescence in conjunction with surface tension measurement, we investigated adsorption behavior of [C$_{\mathrm{12}}$mim]Cl, [C$_{\mathrm{12}}$mim]Br, [C$_{\mathrm{12}}$mim]I aqueous solutions, in which the surface is first covered by [C$_{\mathrm{12}}$mim]$^{\mathrm{+}}$ cations at low concentrations, and the adsorption of the halide anions to this charged interface would follow with the increase in the concentration of solutes. From the surface tension measurements, it was observed that critical micelle concentration of [C$_{\mathrm{12}}$mim]I solution was 4.6 mM, much smaller than that of [C$_{\mathrm{12}}$mim]Cl (16.7 mM) indicating surface activity of surfactant increases with size of halide anions. From X-ray fluorescence, surface excess of halide anion was measured quantitatively from the interface of these solutions. By putting NaCl and NaI in [C$_{\mathrm{12}}$mim]I and [C$_{\mathrm{12}}$mim]Cl solutions, respectively, competition between Cl$^{\mathrm{-}}$~and I$^{\mathrm{-}}$~adsorption was investigated, to find that I$^{\mathrm{-}}$ has stronger adsorption on the charged surface than Cl$^{\mathrm{-}}$. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J2.00013: Interaction between M/CuO (M$=$ Ti, V, Cr, Mn) as studied by X-ray Photoelectron Spectroscopy Anil Chourasia, Jacob Stahl The technique of x-ray photoelectron spectroscopy has been utilized to investigate the chemical reactivity between metal M (where M is Ti, V, Cr, or Mn) and copper oxide at the M/CuO interface. Thin films of copper (about 20 nm) were deposited on silicon substrates by the e-beam method. Such samples were oxidized in an oxygen environment in a quartz tube furnace at 400$^{\circ}$C. The formation of CuO was checked by the XPS spectral data. Thin films of the metal M were then deposited on these CuO sample. The M 2p, oxygen 1s and copper 2p regions were investigated by XPS. The magnesium anode (energy $=$ 1253.6 eV) has been used for this purpose. The metal 2p peaks shift to the high binding energy side while the satellites associated with the copper core level peaks disappear. The shifting of the metal 2p peaks is associated with the formation of the oxide. The disappearance of the satellites in the copper 2p region is associated with the reduction of copper oxide to elemental copper. The spectral data show chemical reactivity at the M/CuO interface. [Preview Abstract] |
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