Estimating surface diffusion coefficients

Seebauer, Edmund G.; Allen, C. E.

doi:10.1016/0079-6816(95)00039-2

Cited by 342 publications

(120 citation statements)

References 251 publications

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“…This is in agreement with the fast diffusion of CO on platinum (111) terraces under UHV conditions with a typical hopping rate in the order of 10 5 s -1 at 195 K and low CO coverage [19][20][21] and 10 7 s -1 at 300 K and CO coverage of 0.67 M [22]. From reviewing over 500 systems Seebauer et al concluded an apparent insensitivity of diffusional parameters to the presence of an aqueous ambient [23], which suggests that a high hopping rate of CO should be expected under electrochemical conditions as well. Having determined the apparent rate constant k of CO oxidation and taking into account the requirements for k/D for the mean field approximation to be valid, we have estimated the diffusion coefficient D for CO on (111) terraces to be higher than 10 -11 cm 2 /s [10].…”

Section: Co Electrooxidation On Ptsupporting

confidence: 61%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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The electrochemical oxidation of carbon monoxide and methanol on single-crystal noble metal electrodes has been studied using cyclic voltammetry, chronoamperometry, in situ FTIR spectroscopy, online electrochemical mass spectrometry, and theoretical methods. The oxidation of CO was found to be enhanced by steps and defects. Furthermore, the surface diffusion rate was found to have a significant influence on the kinetics of the oxidation process: for high diffusion rates, such as the oxidation of CO on platinum, the kinetics can be described by a mean field model, while for low diffusion rates, such as CO oxidation on rhodium in sulfuric acid, a nucleationand-growth model was found to be more suitable. Voltammetric and mass spectrometric measurements on the oxidation of methanol on platinum indicate that steps enhance the overall reaction rate. In general, the selectivity towards the direct oxidation pathway through soluble intermediates was found to be higher in the absence of strongly adsorbing anions. In both perchloric and sulfuric acid, this selectivity was also found to increase with increasing step density. In sulfuric acid, Pt(111) shows the highest relative contribution for the direct pathway of all surfaces studied in that electrolyte. Based on these results, a detailed reaction scheme for the electrochemical oxidation of methanol is presented.

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Section: Co Electrooxidation On Ptsupporting

confidence: 61%

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

et al. 2007

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“…Atomic diffusion has been studied for a long time as one of the fundamental processes governing the surface physics [1][2][3][4][5][6]. For example, the diffusion of atoms is responsible for epitaxial growth of atomic layers, formation of islands, chains, and other nanostructures or chemical reactions.…”

Section: Introductionmentioning

confidence: 99%

Surface diffusion of Pb atoms on the Si(553)-Au surface in narrow quasi-one-dimensional channels

et al. 2014

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The one-dimensional diffusion of individual Pb atoms on the Si(553)-Au surface has been investigated by a combination of scanning tunneling microscopy (STM), spectroscopy (STS), and first-principles density functional theory. The obtained results unambiguously prove that the diffusion channels are limited to a narrow region between Au chains and step edges of the surface. Much wider channels observed in STM and STS data have electronic origin and result from an interaction of Pb with surface atoms. The length of the channels is determined by a distance between defects at step edges of the Si(553)-Au surface. The defects can act as potential barriers or potential wells for Pb atoms, depending on their origin.

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“…Note, however, that the maximum rates of surface diffusion and reaction may substantially deviate from the bulk-derived estimates depending on the reaction system and conditions. 62,63 Levoglucosan and abietic acid substrates were exposed under dry conditions to OH in the presence of O 2 using a coated-wall flow-tube reactor coupled to a chemical ionization mass spectrometer as described in detail previously. 29 In brief, OH radicals were produced via a microwave discharge of H 2 in a He carrier flow followed by reaction with O 2 in a movable halocarbon wax-coated glass injector.…”

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confidence: 99%

Multiphase Chemical Kinetics of OH Radical Uptake by Molecular Organic Markers of Biomass Burning Aerosols: Humidity and Temperature Dependence, Surface Reaction, and Bulk Diffusion

et al. 2015

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Multiphase reactions of OH radicals are among the most important pathways of chemical aging of organic aerosols in the atmosphere. Reactive uptake of OH by organic compounds has been observed in a number of studies, but the kinetics of mass transport and chemical reaction are still not fully understood. Here we apply the kinetic multilayer model of gas−particle interactions (KM-GAP) to experimental data from OH exposure studies of levoglucosan and abietic acid, which serve as surrogates and molecular markers of biomass burning aerosol (BBA). The model accounts for gas-phase diffusion within a cylindrical coatedwall flow tube, reversible adsorption of OH, surface-bulk exchange, bulk diffusion, and chemical reactions at the surface and in the bulk of the condensed phase. The nonlinear dependence of OH uptake coefficients on reactant concentrations and time can be reproduced by KM-GAP. We find that the bulk diffusion coefficient of the organic molecules is approximately 10 −16 cm 2 s −1, reflecting an amorphous semisolid state of the organic substrates. The OH uptake is governed by reaction at or near the surface and can be kinetically limited by surface-bulk exchange or bulk diffusion of the organic reactants. Estimates of the chemical half-life of levoglucosan in 200 nm particles in a biomass burning plume increase from 1 day at high relative humidity to 1 week under dry conditions. In BBA particles transported to the free troposphere, the chemical half-life of levoglucosan can exceed 1 month due to slow bulk diffusion in a glassy matrix at low temperature. ■ INTRODUCTIONBiomass burning is one of the largest sources of primary organic aerosols, black carbon, 1 and trace gases in the Earth's atmosphere with a source strength comparable to fossil fuel burning.2−4 Biomass burning aerosol (BBA) has a significant impact on climate and public health. BBAs are ubiquitous and via pyro-convection can also reach the upper troposphere and lower stratosphere regions of the atmosphere. 5−9 They scatter or absorb solar radiation and can serve as cloud condensation nuclei and ice nuclei affecting cloud microphysical and radiative properties. 10,11 Black and brown carbon produced from incomplete combustion are important contributors to the radiative forcing, 12,13 and polycyclic aromatic hydrocarbons (PAHs) associated with BBA can cause adverse health effects such as oxidative stress. 14−16Several field campaigns and remote sensing studies have been performed to investigate the impact of biomass burning on local, regional, and global scales.17−21 The contribution of biomass burning emissions to field-collected particles is typically evaluated by applying chemical receptor-based models, which utilize source-specific molecules, also termed biomolecular markers, found in the particles to identify the source and estimate aerosol source strength. 22 Levoglucosan (1,6-anhydro-β-D-glucopyranose, C 6 H 10 O 5 ) and abietic acid (1-phenanthrenecarboxylic acid, C 20 H 30 O 2 ) are produced during lignin and hemicellulose combust...

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Estimating surface diffusion coefficients

Cited by 342 publications

References 251 publications

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

Surface diffusion of Pb atoms on the Si(553)-Au surface in narrow quasi-one-dimensional channels

Multiphase Chemical Kinetics of OH Radical Uptake by Molecular Organic Markers of Biomass Burning Aerosols: Humidity and Temperature Dependence, Surface Reaction, and Bulk Diffusion

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