Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V31: Surfaces and Adsorbates (SA)Focus
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Sponsoring Units: DCP Chair: Silvina Gatica, Howard University Room: BCEC 203 |
Thursday, March 7, 2019 2:30PM - 3:06PM |
V31.00001: TBD Invited Speaker: Svetlana Mintova TBD |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V31.00002: Methane Adsorption on Zeolitic Imidazolate Framework -8 (ZIF-8) Dinuka Har Gallaba, Aldo Dante Migone Zeolitic Imidazolate frameworks (ZIFs) are porous Metal Organic Framework materials that have zeolite-like structures. ZIF -8 has shown structural transition when adsorbing gas molecules, this leads to increment in loading. This has been previously observed with N2, CO, O2 and Xe adsorption. Adsorption studies of energy related gasses are great significant to the petroleum and automotive industries. Among those gasses methane is a good alternative to petroleum based fuels. We present the results of an experimental study of methane sorption in ZIF-8. We measured isotherms at five different temperatures between ~ 85 K and 107 K. We have observed three sub-steps in each of the isotherms. The intermediate sub-step had not been observed experimentally in previous studies of this system. We measured a sharp increase in the equilibration times at loadings corresponding to the intermediate sub-step in the isotherms. We have explored the isosteric heat of adsorption, and its dependence on sorbent loading, for this system. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V31.00003: Improving the Adsorption Selectivity of CO2/CH4 by Strength, Shape and Kinetics Silvina Gatica Gas separation by adsorption can be accomplished by three basic physical mechanisms: equilibria, kinetics, and steric effects. Equilibrium mechanisms rely on the strength of attraction between gas molecules and their substrate. For example, the interaction of CO2 with a substrate is usually stronger than methane-substrate. As a result, the equilibrium mechanism presents a plausible strategy to separate carbon dioxide from mixtures. We have studied the adsorption of CO2/CH4 mixtures on various substrates by Monte Carlo and Molecular Dynamics simulations. Our findings show that on substrates including MOFs, carbon nanohorns and graphene, the selectivity of adsorption of CO2/CH4 at room temperature is low (near 1). We explore the kinetics and steric effects on the selectivity, finding that the combination of the three above-mentioned mechanisms can significantly boost the CO2/CH4 separation at 300K. In this talk, I will present a review of the various cases studied. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V31.00004: Hydrogen Adsorption on Pt(111) Revisited from Random Phase Approximation Lei Yan, Yang Sun, Yoshiyuki Yamamoto, Shusuke Kasamatsu, Ikutaro Hamada, Osamu Sugino It is generally believed that H is predominantly adsorbed on the fcc site of Pt(111), as supported by the calculations using density functional theory (DFT) within generalized gradient approximation (GGA). Experiments, however, observe the signal from the top site. Similar problem exists in CO/Pt(111), where GGA is known to wrongly predict the fcc site as the most stable site, for which a correct answer was given recently using a more advanced correlation functional called random phase approximation (RPA). Here we attack this H/Pt(111) problem using DFT-RPA [1]. By using DFT within the exchange-correlation functionals of different level, we evaluate the stability of fcc adsorption site relative to the top site. The most advanced one based on the RPA, is found to revise our knowledge so far derived from the conventional functionals. Two adsorption sites are hereby found to compete sensitively depending on lattice spacing of the surface, mass of the hydrogen isotope, and hydrogen coverage. The revised knowledge provides natural explanation for the controversy regarding the electrochemical and spectroscopic data, giving impact on the research on the fuel-cell reaction mechanism. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V31.00005: ADSORPTION OF PHENOL IN ZEOLITES: MULTI-TECHNIQUE MODELING Hicham Jabraoui, Guillaume Maurin, Sébastien Lebègue, Ibrahim Khalil, Karine Thomas, Francoise Maugé, Michael Badawi Protonated zeolites were explored as effective adsorbent materials for removing phenol from biofuels using multi-scale modeling. Here, we used a powerful combination of the multiple modeling techniques: i) Density Functional Theory (DFT) [1],[2] allows to determine binding energies of several configurations of guest molecule in zeolites ii) Grand Canonical Monte Carlo (GCMC) [3],[4] shows how much molecules can zeolite hold, i.e. the adsorption capacity as intermolecular interactions at high loading, iii) ReaxFF Molecular Dynamics (RFF-MD) [5] allows knowing both the mobility of molecules within the zeolite framework, and the structure of molecule-loaded faujasite. The obtained results are compared with those measured by different experimental tools (Infrared Spectroscopy, breakthrough curves, and desorption experiments). We will show that USY zeolites provide a good regenerability of the zeolites as a high adsorption capacity. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V31.00006: Adsorption and Separation of CO2 and CH4 Gas Mixture in a Graphene Layer and a Graphite Surface Hind Aljaddani, Silvina Gatica The goal of this work is to predict the selective adsorption of CO2 from a mixture with CH4 on a graphene/graphite substrate. The substrate consists on a layer of graphene with slits suspended on top of graphite at a distance of 10 Å. Molecular dynamics was used to simulate this adsorption. In this system, methane is modeled as a single, spherical atom with one Lennard-Jones site.Carbon dioxide is modeled as a linear rigid body with three Lennard-Jones sites and three partial charges. The slits in graphene are made by deleting carbon atoms from the lattice within a region of specified width. Graphite is modeled as a 10-4-3 wall. We run the simulations at 300K and compare the selectivity of CO2/CH4on the substrate to test the capability of the graphene/graphite to separate CO2 from CH4.The result shows that the selectivity is higher for narrow slits. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V31.00007: Impact of nuclear vibrations on van der Waals interactions and radiative heat transfer in graphene Prashanth Venkataram, Jan Hermann, Teerit Vongkovit, Alexandre Tkatchenko, Alejandro Rodriguez We apply a recent theoretical framework describing thermal and quantum electromagnetic phenomena arising from the coupling of photons and phonons in molecular systems, including van der Waals interactions and radiative heat transfer, to interactions among parallel sheets of neutral graphene and metallic substrates. In particular, we show that atom-scale features as well as contributions of phonons to the response of graphene, as captured in ab-initio density functional theory calculations, along with long-range retarded electromagnetic fields, are of utmost importance to describing its van der Waals interactions and radiative heat transfer over a broad range of length scales; interactions no longer behave as simple power laws in terms of surface separation and show noticeable temperature sensitivity at separations well below the micron-scale radiative thermal wavelength. The contributions of phonons and atom-scale effects to the response are largely neglected in continuum treatments of the electromagnetic response of neutral graphene, which typically consider only the electronic contributions to the response derived from a tight-binding model; consequently, we observe significant differences in the predictions of our microscopic framework from such macroscopic treatments. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V31.00008: Pseudo-Palladium alloys for catalytic applications Mikael Råsander, J. Andreas Larsson Palladium is a commonly used catalyst for the formation of C-C, C-O and C-N bonds in pharmaceutical manufacturing. However, Palladium is expensive which results in high production costs. In this project, we have used computational modelling based on density functional theory to search for possible combinations of elements which mimic the behavior of Palladium in order to lower the cost of production. We have investigated both bulk as well as nanoparticles of, e.g., Rh0.5Ag0.5, Pd1-xCux and Pd1-xAgx alloyed systems and found that these systems have Palladium-like electronic properties and are therefore expected to have similar catalytic properties as pure Palladium. The Pd1-xCuxand Pd1-xAgxsystems have Palladium-like electronic structures up to about 25% Cu or Ag, respectively. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V31.00009: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 4:42PM - 4:54PM |
V31.00010: Theoretical Studies of Activation Energies and Pre-Exponential Factors of Alcohol Dehydrogenation on Cu Wei Chen, Robert J. Madix, Cynthia M. Friend, Efthimios Kaxiras We study the thermodynamic and kinetic processes involved in the anhydrous dehydrogenation of linear-chain alcohols on the Cu(110) surface using multiscale approaches. We determine the kinetic barriers for the two dehydrogenation steps, namely, the O–H and the subsequent C–H bond-breaking on Cu. The reaction of methoxy-to-formaldehyde has a rather high-energy transition state, in contrast to that of alkoxide-to-aldehyde in the longer-chain systems. This difference qualitatively explains the lower production efficiency of formaldehyde on Cu. We also use a Monte Carlo sampling to calculate the entropies of initial and transition states. The estimated pre-exponential factors, beyond the harmonic approximation, are found to have a molecular size dependence. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V31.00011: Kinetics of ligands mediated ultra-small silver cluster formation. Mohsen Farshad, Dylan Suvlu, Jayendran C Rasaiah We discuss a kinetic mechanism that predicts different average size distributions of silver clusters with peak diameters around 0.7 nm and 1.2 nm in solution depending on the initial conditions in a redox reaction. Nanoparticle growth occurs through ligand addition and eleimination followed by irreversible dimerization and reversible ligand-monomer addition to the seed cluster. We have also incorporated the coalescence of clusters which can dominate the growth of silver nanoparticles in the presence of a strong reductant. Our calculations provide further insight into the mechanistic details of ultra-small silver cluster formation from an atomic perspective. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V31.00012: Boron-doped silicene as a promising anode for Li-ion batteries Alex Chen, Xuan Luo Two-dimensional (2D) materials as electrodes are the trend for future Li-ion battery technology. By using first-principles calculations, we investigate the adsorption of Li-ions on boron-doped silicene as a potential electrode material. We identified the most stable adsorption sites and their corresponding adsorption energies for the adsorption of Li adatoms on the doped silicene. Then, we increase the ion concentration to examine the impact of Li-ions on the stability and structure of the material. With Bader charge analysis, we confirm the charge transfer from the Li-ion to doped silicene and use that to calculate a high specific capacity for the B-doped silicene. We then used the nudged elastic band method to analyze the energy barriers of Li-ion diffusion along the surface and through the hexagonal hollow of the monolayer. Our findings reveal the potential application of B-doped silicene as an electrode material in lithium batteries. |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V31.00013: Direct Determination of the Thermodynamic Properties of Melting for Amino Acids Yeong Zen Chua, Amir Abdelaziz, Dzmitry Zaitsau, Sergey Verevkin, Christoph Held, Christoph Schick The properties of melting are used for the prediction of solubility of solid compounds. Unfortunately, by using the conventional DSC or adiabatic calorimetry direct determination of the melting enthalpy and melting temperature is often not possible for biological compounds due to the decomposition during the measurement. The apparent activation energy of decomposition is at least one order of magnitude smaller than that of melting. This allows shifting of the decomposition process to higher temperature without seriously disturbing the melting by applying very high heating rates. High scanning rates up to 2●104 K●s-1 are utilized with fast-scanning calorimeter Mettler Toledo Flash DSC1, which employs thin film chip sensors with sub µJ●K-1 addenda heat capacities. With the help of this technique the melting parameters for a series of amino acids were successfully determined. The ultra-fast cooling of the melted samples allows the studied compounds to retain in the liquid state and to determine for the first time its glass transition temperatures. The results are in reasonable agreement with the simulated PC-SAFT values. |
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