Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J34: Environmental Interfaces V |
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Sponsoring Units: DCP Chair: Barbara Finlayson-Pitts, UC Irvine Room: Convention Center 511 A |
Tuesday, March 22, 2005 11:15AM - 11:51AM |
J34.00001: Chemical Reactivity at Metal Oxide-Aqueous Solution Interfaces Invited Speaker: Gordon E. Brown, Jr. The chemical reactivity of metal oxide surfaces in contact with aqueous solutions, with respect to cations and anions, is controlled by the composition, structure, and charging properties of the surface, the dielectric properties of the bulk oxide, and the stability of the aqueous cation or anion complex versus its sorption complex. These points will be illustrated for selected cations, anions, and metal oxides using macroscopic uptake and EXAFS spectroscopy results, x-ray standing wave data, and crystal truncation rod diffraction data. The reactivity of metal oxide surfaces with respect to low molecular weight (LMW) carboxylic acids is also dependent on the types of ring structures formed between surface functional groups and the LMW organic molecules. These types of interactions will be illustrated using ATR-FTIR data and dissolution measurements as a function of pH for oxalate, maleate, phthalate, and pyromellitate interacting with boehmite (AlOOH). \newline \newline Co-Authors are Tae Hyun Yoon, Stephen B. Johnson, Dept. of Geological \& Environmental Sciences, Stanford University, Stanford CA 94305-2115; Thomas P. Trainor, Dept. of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK 99775; Anne M. Chaka, National Institute of Standards and Technology, Gaithersburg, MD 20899 [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:03PM |
J34.00002: Water dissociation on TiO$_{2}$(110): application of the reactivity mapping method Jorge Sofo, Elam Leed We have recently developed a method to calculate the chemical reactivity of a surface with respect to water dissociation. The method is based on one calculation of the electronic states and provides a map of the activity of different sites at the surface. We present an application to the water physisorption and chemisorption process on the (110) surface of TiO$_{2}$ in the rutile structure. The predictions of this chemical reactivity mapping method are in excellent agreement with more conventional method of calculation chemical reactivity, including ab-initio molecular dynamics. As a result of its simplicity it is possible to study larger surface areas including the effect of correlations and catalytic effects. [Preview Abstract] |
Tuesday, March 22, 2005 12:03PM - 12:15PM |
J34.00003: Two-dimensional hydration shells of alkali metal ions at a hydrophobic surface Sheng Meng, Dinko V. Chakarov, Bengt Kasemo, Shiwu Gao We study the hydration shell formation of alkali metal ions at a graphite surface. Two-dimensional (2D) shell structures are found in the initial stage of hydration, in contrast to the 3D structures in bulk water and clusters. Comparison of vibrational spectra with experiments identifies the shell structures and the thermally induced transition from the first to the second shell. We also found intriguing competition between hydration and ion-surface interaction, leading to different solvation dynamics between K and Na. Implications of these results in ionic processes at interfaces are elaborated. [Preview Abstract] |
Tuesday, March 22, 2005 12:15PM - 12:51PM |
J34.00004: Surface Chemistry of Environmentally Important Minerals Invited Speaker: Motion of surface ions is integral in the dissolution and growth dynamics of carbonate minerals. The present study investigates the density and the mobility of surface ions and the structure of the adsorbed water layer with changes in relative humidity (RH). The time evolution of the polarization force, which is induced by an electrically biased tip of an atomic force microscope, shows that the density and the mobility of surface ions increase with rising humidity, a finding which is consistent with increasing surface hydration. A marked change in the observations above 55{\%} RH indicates a transition from a water layer formed by heteroepitaxial two- dimensional growth at low RH to one formed by multilayer three-dimensional growth at high RH. A comparison of the results of several rhombohedral carbonates (viz. CaCO$_{3}$, FeCO$_{3}$, ZnCO$_{3}$, MgCO$_{3}$, and MnCO$_ {3})$ shows that a long relaxation time of the polarization force at high RH is predictive of a rapid dissolution rate. This finding is rationalized by long lifetimes in terrace positions and hence greater opportunities for detachment of the ion to aqueous solution (i.e., dissolution). Our findings on the density and the mobility of surface ions help to better constrain mechanistic models of hydration, ion exchange, and~dissolution/growth. \\ \\Co-authors are Young-Shin Jun, Treavor Kendall, and Owen Duckworth. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J34.00005: A Theoretical Study of Copper Adsorption on the (110) Surface of TiO2 Scott J. Thompson, Steven P. Lewis Strong interactions between metal catalysts and their supporting oxide substrates give rise to enhanced catalytic properties. Using Density Functional Theory, we are exploring this phenomenon for the prototypical system of copper on the (110) surface of rutile TiO2. In this talk, we will present our results for the first stages of this investigation, including predictions of the optimal binding site and binding energy for Cu at various coverages and on both stoichiometric and reduced TiO2 (110) surfaces. Connections will be drawn to recent experiments, and an overview of our ongoing investigations will be presented. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J34.00006: A theoretical study of adsorption of NO on RuO$_2$(110) Sampyo Hong, Talat Rahman Experiments suggest that while RuO$_{2}$(110) is a highly reactive surface for CO oxidation, the same is not the case for NO adsorbed on this surface [1]. In order to understand the rationale for this difference, we have carried out \textit{ab initio} electronic structure calculations to examine the idiosyncrasies in the adsorption, dissociation, and oxidation processes for CO and NO on RuO$_{2}$(110). Our calculated geometry and adsorption energies for NO adsorption are in good agreement with experiments available. Our results confirm that while CO can easily oxidize on this surface [2], NO does not bind easily to the bridging O atoms to produce NO$_{2}$. Detailed analysis of the surface electronic structure, including the charge transfer, charge density distribution and local electronic density of states together with its hybridization is pesented to compare and contrast the energetics and dynamics of CO and NO on RuO$_{2}$(110). [1] Y. Wang, K. Jacobi, and G. Ertl, J. Phys. Chem. B \textbf{107}, 13918 (2003). [2] Z. Liu, P. Hu, A. Alavi, J. Chem. Phys. \textbf{114}, 5956 (2001). [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:51PM |
J34.00007: The Unusual Adsorption and Reaction Chemistry of NOx on Oxide Surfaces Invited Speaker: First-principles atomistic simulations based on density functional theory have reached a state of development that they now provide a powerful complement to experiment in the effort to understand, control, and optimize heterogeneous catalytic processes. While these methods have been extensively applied to metal surface reactions, metal oxides have received less attention. In this work two examples of current research in oxide surface chemistry relevant to the catalytic reduction of NO$_{x}$ ($x $= 1, 2) to N$_{2}$ in the presence of a large excess of interfering O$_{2}$ will be discussed. We first consider the nature and origins of NO$_{x}$ ``cooperative'' adsorption on basic metal oxides like the alkaline earths, the surprisingly strong adsorption enhancement arising from electron transfer between neighboring surface adsorbates. We then discuss the catalytic oxidation of NO to NO$_{2}$ on transition metal oxides, in particular contrasting with the superficially similar oxidation of CO to CO$_{2}$. In both cases, the combination of NO$_{x}$ with metal oxide is found to lead to novel and unanticipated behavior---behavior that could be exploited for improved catalytic function. [Preview Abstract] |
Tuesday, March 22, 2005 1:51PM - 2:03PM |
J34.00008: Thermodynamics of toxic gas molecules on metal oxide nano powders Jae-yong Kim, Ik-Jae Lee, Chae-ok Kim Studies on physical/chemical reactions of gas molecules on nano sized metal oxide powder surface is interesting because the results from the research can directly be applied to the investigation of the surface mediated catalytic reactions aimed at reducing atmospheric pollutants. Thermodynamic properties of nitrous oxides (NO$_{x})$ on varies nano sized metal oxides such as MgO and ZnO powders were studied using a computer controlled gas adsorption isotherm apparatus, which has good temperature stability within 0.01K in a wide rage and good pressure accuracy with a resolution better than 10$^{-5}$ torr in 100 torr. A set of isotherms below the triple points of the nitrous gas was measured. A specific surface area of particles was also obtained from calculations of a molecular area of adsorbate gas on the surface of the adsorbents. The thermodynamic results including compressibility and isosteric heat of adsorption of nitrous gases on various metal oxide surfaces will be presented. [Preview Abstract] |
Tuesday, March 22, 2005 2:03PM - 2:15PM |
J34.00009: Density-functional study of chemical reactions at a solid-fluid interface: passivation of the (0001) surface of Cr$_2$O$_3$ Sahak Petrosyan, Angeliki Rigos, Tomas Arias Using a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a dielectric environment, we present the first detailed study of the impact of a solvent on the surface chemistry of Cr$_2$O$_3$, the passivating layer of stainless steel alloys. Compared to vacuum, we predict that the presence of water has little impact on the adsorption of chloride ions to the oxygen-terminated surface but a dramatic effect on the binding of hydrogen to that surface. These results indicate that the dielectric screening properties of water are important to the passivating effects of the oxygen-terminated surface. [Preview Abstract] |
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