Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z43: Catalysis and Chemical Reaction Dynamics |
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Sponsoring Units: DCP Chair: James Skinner, University of Wisconsin Room: Hilton Baltimore Holiday Ballroom 2 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z43.00001: Room-temperature self-cleaning molecular sensing by catalytic reactions Keith H. Warnick, Bin Wang, David E. Cliffel, David W. Wright, Richard F. Haglund, Sokrates T. Pantelides New sensing techniques using self-cleaning nanosensors for molecular detection are in demand. Here we describe a room-temperature process in which a nanostructured substrate catalyzes the reaction of a target molecule with atmospheric oxygen and the reaction energy is absorbed by the substrate, where it can in principle be detected. Specifically, we report first-principles calculations describing a reaction catalyzed by Fe-porphyrin at room temperature that breaks O$_{2}$, incorporates an oxygen into the methyl group of 2,4-dinitrotoluene (DNT) and releases 1.9 eV per reaction. The atomic oxygen left on the Fe site can be removed by reacting with another DNT molecule, making the whole process self-cleaning. The reaction energy absorbed by the substrate can in principle be detected optically, as for example, by detecting the metal-insulator phase transition in VO$_{2}$. We further explore issues of sensitivity and selectivity in exploiting this reaction for solid-state molecular sensing. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z43.00002: A density functional theory study of structure-property relationships for Pt-Ni alloy catalysts Liang Cao, Tim Mueller The ORR (Oxygen Reduction Reaction) is an important reaction in devices such as metal-air batteries and PEMFCs (Polymer Electrolyte Membrane fuel cells). Pure Pt is one of the most successful electrode catalysts for this key reaction. However, due to its expense, numerous efforts have been made to find a new catalysis system based on Pt bimetallic alloys, in which Pt is partially replaced by less expensive metals, such as Ni, Co and Fe. Experimental and theoretical works have shown that Pt3Ni alloys have a higher ORR activity than pure Pt. In order to investigate the enhanced catalytic activity, cluster expansions corresponding to a simplified 9-layer Pt-Ni slab model are built to accurately and quickly predict the energies of surfaces as a function of atomic order. With the help of this model, we can study systematically the atomic structure and the surface geometry of Pt3Ni surface system at a variety of temperature and chemical environments, and we can calculate the adsorption binding energies of O, OH and H on both equilibrium and non-equilibrium Pt-Ni(111) surfaces. Also, we can investigate the effects of off-stoichiometry on surface by searching for stable ground states under different concentrations. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z43.00003: First-principles design of a dynamically tunable catalyst for CO$_{2}$ capture and conversion Babatunde Alawode, Alexie Kolpak Due to its role in climate change, there is great interest in finding ways to take advantage of the vast amount of waste CO$_{2}$ we produce by its conversion to useful substances. This approach is currently impractical due to the high temperatures and pressures generally required for the synthesis of compounds using CO$_{2}$ as a precursor. To make direct CO$_{2}$ capture and conversion economically viable, new materials able to catalyze the conversion reactions at significantly milder conditions will be essential. In this work, we use DFT computations to design a dynamically tunable ferroelectric oxide-supported thin film catalyst that can capture CO$_{2}$ directly from the emission stream and convert it into methanol. One promising candidate for a dynamically tunable catalyst of this type is Zn$_{\mathrm{x}}$O$_{\mathrm{y}}$/PbTiO$_{3}$. We demonstrate that switching the polarization of the ferroelectric substrate substantially changes the surface atomic and electronic properties of the heterostructure, thereby alternately encouraging strong CO$_{2}$ adsorption and desorbing the products. Our approach may lead not only to new technologies for reducing emissions, but also to novel catalysts that could decrease energy consumption for industrial-scale synthetic processes. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z43.00004: Preferential condensation of $\beta$ RDX on In metal surfaces Terrence Jach, Ilana G. Goldberg, Fernando D. Vila The energetic compound cyclotrimethylene-trinitramine (RDX) normally crystallizes out of solution at standard temperature and pressure in the $\alpha$ form. This consists of two nitro groups in pseudoaxial positions in relation to the C-N ring, and one nitro group in a pseudoequatorial position in an orthorhombic lattice. A metastable phase, labeled the $\beta$ phase, is difficult to create and rarely observed. It consists of all three nitro groups in pseudoaxial positions, occupying a trigonal lattice. We have observed by means of Raman spectroscopy that RDX crystallized from solution on In metal foil preferentially adopts the $\beta$ phase. We discuss a possible mechanism for this behavior in the context of recently published DFT calculations for RDX on a metal cluster. [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z43.00005: Catalytic properties of Pt nanoclusters on defective graphene Ioanna Fampiou, Ashwin Ramasubramaniam Metal nanoparticles on carbon supports hold promise as electrocatalysts in direct methanol fuel cells, proton-exchange membrane fuel cells, and hydrogen fuel cells. Pt nanoclusters on carbon supports have been shown to possess superior catalytic activity and increased selectivity in a variety of electrochemical reactions as compared to bulk Pt electrodes; however, the underlying mechanisms remain poorly understood. We examine the interaction of Pt nanoclusters with point defects in graphene using first-principles density functional theory. The presence of defects in graphene supports enhances the Pt-carbon bonding, which suppresses cluster sintering thus allowing for sustained catalytic performance. Furthermore, stronger binding of clusters at defects is found to increase the tolerance of bound Pt nanoparticles towards CO poisoning. Finally, we examine the role of defective graphene supports on the activity of the cluster for the CO oxidation reaction and obtain estimates for CO-oxidation kinetics. Our results suggest possible avenues for controlling the dispersion and catalytic activity of Pt nanoclusters on carbon supports via defect engineering. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z43.00006: Catalytic Role of Au Nanowires Edison da Silva, Ana Paula F. Nascimento, Miguel A. San-Miguel The oxidation of CO in linear atomic chains (LACs) of Au nanowires (NW) is studied by means of density functional theory calculations using quasi-static (T=0) and finite temperature {\it ab initio} molecular dynamics simulations. The adsorption of O$_2$ and CO molecules on the LAC lead to the formation of an intermediate O$_2$CO complex. Upon thermal activation at room temperature, the complex is able to proceed to oxidation forming a CO$_2$ molecule and leaving an atomic O impurity into the Au LAC. We report the conditions under which this oxidation pathway takes place. This process also explains the appearance of unusual large Au-Au bond distances in the LAC and attributed to the presence of atomic impurities. [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z43.00007: Rationale for the high reactivity of the interfacial sites in methanol reaction on Au/TiO2(110) Sampyo Hong, Talat Rahman We have performed density functional theory calculations of methanol decomposition on gold nanoparticle supported on a partially reduced TiO2(110) surface. Our calculations show that the adsorption geometry of 13 atom gold nanoparticle strongly depends on the reduction level of the TiO2(110) surface such that a 30{\%} reduced TiO2(110) surface prefers a hemispherical shape while a 10{\%} reduced TiO2(110) surface prefers a flat shape. This hemispherical geometry of gold nanoparticle has a highest density of interfacial sites among the investigated geometries (flat, spherical, hemispherical ones), which may be a reason for the known high reactivity of interfacial sites towards various reactions on supported gold nanoparticles. We have found that methanol decomposition reaction occurring in the interfacial sites is much facile than that occurring in the non-interfacial sites of TiO2(110) surface in agreement with experiment [1]. We have found that the high activity of the interfacial sites is in fact, a result of charge transfer induced Coulomb interaction among the gold, reactant, and reducible TiO$_{\mathrm{2\thinspace }}$atoms through the formation of ionic O-Au bond between gold and methoxy in the active sites, which turns the participating perimeter gold atom cationic. A direct result of such charge transfer induced repulsion is tilting of the methoxy axis, which leads to facile reaction of methoxy through C-H scission with the bridge oxygen atoms that are readily available from the reducible support. Work supported by DOE Grant No. DE-FG02-07ER15842. [1] S. A. Tenney, B. Cagg, M. Levine, W. He, K. Manandhar, and D. A. Chen, \textit{Surf. Sci.} 606, 1233 (2012). [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z43.00008: Dispersion-corrected first-principles calculation of terahertz vibration, and evidence for weak hydrogen bond formation Masae Takahashi, Yoichi Ishikawa, Hiromasa Ito A weak hydrogen bond (WHB) such as CH--O is very important for the structure, function, and dynamics in a chemical and biological system WHB stretching vibration is in a terahertz (THz) frequency region Very recently, the reasonable performance of dispersion-corrected first-principles to WHB has been proven. In this lecture, we report dispersion-corrected first-principles calculation of the vibrational absorption of some organic crystals, and low-temperature THz spectral measurement, in order to clarify WHB stretching vibration. The THz frequency calculation of a WHB crystal has extremely improved by dispersion correction. Moreover, the discrepancy in frequency between an experiment and calculation and is 10 1/cm or less. Dispersion correction is especially effective for intermolecular mode. The very sharp peak appearing at 4 K is assigned to the intermolecular translational mode that corresponds to WHB stretching vibration. It is difficult to detect and control the WHB formation in a crystal because the binding energy is very small. With the help of the latest intense development of experimental and theoretical technique and its careful use, we reveal solid-state WHB stretching vibration as evidence for the WHB formation that differs in respective WHB networks [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z43.00009: Superior Long range Electric Transport of Organometallic Wire via Stepping Stone mechanism and First Principles Study of Length dependence of Thermoelectric Effects Hisao Nakamura, Takao Ishida, Yoshihiro Asai We revealed the role of metal centers for superior long-range electric transport in organometallic-complex wires via stepping stone mechanism, which is recently proposed in Ref. 1]. We also found that the transport properties of organometallic molecular wire have some advantages to create thermoelectric devices, such as phonon mismatching effect, superior long range transport, and quantum interferences of conducting orbitals. We analyzed the length dependence and metal species dependence of the figure of merit (ZT) with including phonon thermal conductivity based on the first principles calculations. [1] K. Terada, H. Nakamura, K. Kanaizuka, M. Haga, Y. Asai, and T. Ishida, ACS Nano, 6, 1988-1999 (2011). [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z43.00010: Oxygen Molecule Adsorption and Dissociation on Boron-doped Fullerene BC$_{59}$ Shizhong Yang, Lei Zhao, Feng Gao, Guang-Lin Zhao, Ebrahim Khosravi, Diola Bagayoko We studied the oxygen molecule adsorption and dissociation on boron-doped fullerene (B-C$_{59})$ from first principles spin polarized density functional theory method simulation. The results show that O$_{2}$ molecule can be adsorbed and partially reduced on the Pauling sites of B-C$_{59}$. The results are compared with those of nitrogen-doped fullerene (N-C$_{59})$. From the comprehensive simulation results, some implications in catalyst application are given. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z43.00011: Reaction Energies of Oxides using Random Phase Approximation Jun Yan, Jens Hummelshoej, Jens N{\O}rskov Oxides are widely used in industrial heterogeneous catalysis, photo catalysis, electrochemistry and in making batteries and fuel cells. To facilitate the computational engineer and design of novel materials in these fields, it is vital important to quantitatively predict the formation and reactions energies of the oxides. LDA/GGA, the success of which has largely relied on the mysterious error cancellation in the exchange-correlation term, generally failed for these oxides, showing systematic and non-canceling errors. Recently, the use of exact exchange (EXX), plus correlation energy from Random Phase Approximation (RPA) emerges as a promising approach to obtain non-empirical exchange-correlation terms. Exact exchange energy is free of self-interaction error, while RPA correlation energy takes into account dynamic electronic screening and is fully non-local. EXX$+$RPA has shown to systematically improve lattice constants, atomization energies, adsorption energies, reaction barriers for a wide range of systems that have ironic, covalent and van der Waals interactions. In this talk I will present our results comparing RPA and GGA functional for the formation and reaction energies of oxides. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z43.00012: Oxygen vacancy formation in doped ceria: Effects of electron localization and ion local distortion Zhenpeng Hu Density functional theory with plus U approximation has been used to study property of doped ceria, especially oxygen vacancy formation energy on doped CeO$_{\mathrm{2}}$ surface. Surfaces with substitutional dopants having lower valence than Ce(IV) have been studied in detail. Based on our results, there are two factors affecting the formation energy of oxygen vacancy: electron localization to form polaron, and local distortion around dopant while vacancy generating. We discuss related application for these rules in catalysis process. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z43.00013: Two-State Reactivity in Hydrocarbon Oxidation by FeO$+$: New Insight through Temperature Dependent Kinetics Shaun Ard, Josh Melko, Nick Shuman, Albert Viggiano Oxidative activation of C-H and C-C bonds is the rate limiting step in many catalytic applications. Transition metals and their oxides are the active component in numerous catalysts as they have proven to be efficient in the activation of these bonds. We report the temperature dependence of reaction kinetics from 120-700K for reactions of FeO$^{\mathrm{+}}$ with CH$_{\mathrm{4}}$, C$_{\mathrm{2}}$H$_{\mathrm{2}}$, C$_{\mathrm{2}}$H$_{\mathrm{4}}$, and C$_{\mathrm{2}}$H$_{\mathrm{6}}$ for the first time, in an effort to improve the mechanistic understanding, and from that the efficiency of these important reactions. The rate constants were found to decrease smoothly with temperature for each hydrocarbon, except for that with methane which displayed an abrupt change in temperature dependence. The branching fractions for the alcohol producing channels were also found to decrease with temperature for each hydrocarbon, with the exception of ethane where it remained constant. Implications of these results towards catalytic applications and theoretical modeling of these systems will be discussed. Specifically, the role of spin orbit coupling in determining the probability of spin inversion, and thus the importance of the ``two-state reactivity'' model applied to many transition metal oxide and hydrocarbon reactions will be addressed. [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z43.00014: Charge relaxation dynamics of an electrolytic nanocapacitor Vaibhav Thakore, James Hickman Understanding charge relaxation dynamics in confined nanospaces with overlapping electric double layers (EDLs) is critical for the development of efficient electrochemical energy storage, energy conversion and bioelectrochemical sensing devices. Using Lattice Boltzmann (LB) method, results from simulations of an electrolytic nanocapacitor subjected to a step potential at t $=$ 0 are presented here for various degrees of EDL overlap, solvent viscosities, ratios of cation to anion diffusivity and electrode separations. A continuously varying molecular speed dependent relaxation time is proposed for use with the LB equation that, unlike the single relaxation time Bhatnagar-Gross-Krook approximation, recovers the correct microscopic description of molecular collision phenomena and holds promise for enhancing the stability of the LB algorithm. Simulations for large EDL overlap showed oscillatory behavior for ionic current densities as opposed to monotonic relaxation to equilibrium for low EDL overlap. Further, at low solvent viscosities and large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appeared to be purely an effect of nanoscale confinement. [Preview Abstract] |
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