Showing papers on "Chemisorption published in 1998"
TL;DR: In this article, self-consistent density functional calculations for the adsorption of O and CO, and the dissociation of CO on strained and unstrained Ru(0001) surfaces are used to show how strained metal surfaces have chemical properties that are significantly different from those of un-strained surfaces.
Abstract: Self-consistent density functional calculations for the adsorption of O and CO, and the dissociation of CO on strained and unstrained Ru(0001) surfaces are used to show how strained metal surfaces have chemical properties that are significantly different from those of unstrained surfaces. Surface reactivity increases with lattice expansion, following a concurrent up-shift of the metal $d$ states. Consequences for the catalytic activity of thin metal overlayers are discussed.
1,905 citations
TL;DR: In this article, the structure, the electronic properties and the reactivity of supported model catalysts have been studied, in situ, by a large number of surface science techniques, and the possibility to study in situ and at the atomic level simple chemical reactions on supported catalysts.
1,354 citations
TL;DR: In this paper, the authors explored the physicochemical and kinetics of the adsorption of a variety of sulfur-containing hydrocarbons onto Au(111) using helium beam reflectivity and temperature-programmed desorption (TPD) techniques.
Abstract: The energetics and kinetics of the adsorption of a variety of sulfur-containing hydrocarbons onto Au(111) have been explored using helium beam reflectivity and temperature-programmed desorption (TPD) techniques. Simple alkanethiols as well as dialkyl sulfides, dialkyl disulfides, and other sulfur-containing organics were found to adsorb with a low coverage physisorption enthalpy about 20% greater than the heat of vaporization in the bulk. In contrast to the dialkyl sulfides that only physisorb, alkanethiols and dialkyl disulfides also interact chemically with the gold with a chemisorption enthalpy of 126 kJ/mol that is independent of alkyl chain length. The presence of sterically hindering substituent groups on the carbon atom adjacent to the sulfur atom produces, however, a reduction in the chemisorption enthalpy of up to 15%. Temperature-programmed desorption of nonequilibrated, high exposure layers of alkanethiols with eight carbon atoms or longer displayed a second, higher energy, chemisorption peak a...
406 citations
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TL;DR: The electrical and gas sensing properties of chemically deposited zinc oxide (ZnO) films were investigated in this paper, where two activation energy values, 0.3 eV and 0.8 eV, were determined in the temperature range 300-400 K which are attributed to oxygen vacancy (VO) donor and heat of chemisorption of the O2− species.
404 citations
TL;DR: In this paper, the adsorbed oxygen layer by AES, XPS, HREELS, LEED, work function measurements and TPDP was studied, and it was shown that the desorption of O 2 from Au(111) can be described by first-order kinetics with an activation energy for O 2 depletions of 30 kcal−1 near saturation coverage.
307 citations
TL;DR: In this article, the kinetics of CO2reforming of CH4 were studied over Pt supported on TiO2, ZrO2 and Cr2O3, and the catalysts were characterized using chemisorption, X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed hydrogenation (TPH), and temperatureprogrammed surface reaction.
286 citations
TL;DR: In this article, the authors investigated the chemical mechanism of surface enhanced Raman scattering (SERS) on an atomically smooth metal surface using electron energy loss spectroscopy (EELS) and molecular spectrograms.
Abstract: We have investigated the chemical mechanism of surface enhanced Raman scattering (SERS) on an atomically smooth metal surface using electron energy loss spectroscopy (EELS) and molecular spectroscopy simulations. The EEL spectra of pyromellitic dianhydride (PMDA) adsorbed on Cu(100) and Cu(111) are reported. Simulations of the surface-enhanced Raman spectra and electron energy loss spectra (EELS) of pyromellitic dianhydride adsorbed on Cu(100) and Cu(111) are reported. The surface enhanced Raman spectra [J. Chem. Soc. Faraday Trans. 92, 4775 (1996)] and the EEL spectra are shown to be sensitive to crystal face. The relevant excited state observed in the EEL spectrum is not intrinsic to molecular PMDA, but results from chemisorption. The Raman spectra are sensitive to the incident laser polarization on both the (100) and (111) surfaces but in different ways. These observations are shown to be a result of the excited state potential energy surface having different shape, and the respective transition dipole...
273 citations
TL;DR: In this article, the catalytic activity of nanocrystalline doped ceria and Cu-and Ag-modified ceria for the complete oxidation of methane was studied by X-ray diffraction and related to the availability of low-temperature oxygen species.
264 citations
TL;DR: In this paper, layer-by-layer oxidation of Si(001) surfaces has been studied by scanning reflection electron microscopy (SREM), and the oxidation kinetics of the top and second layers were independently investigated from the change in oxygen Auger peak intensity calibrated from the SREM observation.
Abstract: Layer-by-layer oxidation of Si(001) surfaces has been studied by scanning reflection electron microscopy (SREM). The oxidation kinetics of the top and second layers were independently investigated from the change in oxygen Auger peak intensity calibrated from the SREM observation. A barrierless oxidation of the first subsurface layer, as well as oxygen chemisorption onto the top layer, occurs at room temperature. The energy barrier of the second-layer oxidation was found to be 0.3 eV. The initial oxidation kinetics are discussed based on first-principles calculations.
245 citations
TL;DR: In this paper, the basic differences between hydrogen electroadsorption under electrochemical conditions and hydrogen chemisorption in low-pressure gas-phase milieu are discussed and their characteristics discussed.
241 citations
TL;DR: In this article, the authors have clarified the apparent barrierless reaction mechanism of the backbond oxidation of the surface Si by incoming incoming molecules and found that the triplet-to-singlet spin conversion is crucial in explaining the incident energy dependence of the sticking probability of the Si molecules.
Abstract: Oxidation of the Si(001) surface was studied by the first principles calculation technique with spin-polarized gradient approximation. We have clarified the apparent barrierless reaction mechanism of the backbond oxidation of the surface Si by incoming ${\mathrm{O}}_{2}$ molecules. An ${\mathrm{O}}_{2}$ molecule does not attack directly the backbond but the oxidation occurs via metastable chemisorption states on the Si surface. We have also found that the triplet-to-singlet spin conversion is crucial in explaining the incident energy dependence of the sticking probability of ${\mathrm{O}}_{2}$ molecules.
TL;DR: In this paper, the surface reaction probability of an atom or a radical in a reactive gas discharge, its diffusive flux to the wall, spatial density profile and temporal density decay during the postdischarge, are examined.
Abstract: The relations between the surface reaction probability β of an atom or a radical in a reactive gas discharge, its diffusive flux to the wall, spatial density profile and temporal density decay during the postdischarge, are examined. Then, the values of β for H, SiH3, and Si2H5 on a growing a-Si:H film, and CH3 and C2H5 on an a-C:H film are derived from the temporal decay of radical densities during the discharge afterglow by using time-resolved threshold ionization mass spectrometry. For SiH3 on a-Si:H, β=0.28±0.03 in excellent agreement with previous determinations using other experimental approaches, and for Si2H5, 0.1<β<0.3. For H on a-Si:H, 0.4<β<1 and mostly consists of surface recombination as H2, while the etching probability of Si as SiH4 is only e≈0.03 at 350 K in good agreement with other studies of H reaction kinetics on crystalline silicon. At high dilution of SiH4 in H2 the sticking probabilities of Si hydride radicals are affected by the flux of H atoms of hydrogen ions which enhances surfac...
TL;DR: In this article, the reaction of CO 2 and H 2 O to form bicarbonate (HCO − 3 ) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2 (110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometers (HREELS).
TL;DR: In this paper, reflection absorption infrared spectroscopy (RAIRS) was used to investigate the chemisorption of glycine and its fully deuterated analogue d 5 -glycine, vacuum deposited on a clean Cu{110} surface.
TL;DR: In this article, first-principles calculations based on density-functional theory and the pseudopotential method are used to investigate the energetics of adsorption of the series of molecules H 2 O, CH 3 OH, H 2O 2 and HCO 2 H on the TiO 2 (110) surface.
TL;DR: In this article, surface-enhanced Raman spectroscopy (SERS) was used to characterize monolayers formed from benzenethiol (BT), benzenemethanol (BMT), p-cyanobenzenemETHanethanethiol(CBMT) and diphenyl disulfide (DPDS) on roughened gold electrodes, showing that the aromatic ring in BT is tilted relative to the mean surface plane at all applied potentials.
Abstract: Surface-enhanced Raman spectroscopy (SERS) has been used to characterize monolayers formed from benzenethiol (BT), benzenemethanethiol (BMT), p-cyanobenzenemethanethiol (CBMT), diphenyl disulfide (DPDS), and dibenzyl disulfide (DBDS) on roughened gold electrodes. All five species adsorb dissociatively as the corresponding thiolates. The charge transfer and electrostatic interactions between the adsorbates and the surface depend strongly on the applied potential. The aromatic ring in BT is tilted relative to the mean surface plane at all applied potentials. The rings in BMT and CBMT also are tilted, but stepping the potential to positive or negative extremes causes a reduction in surface coverage and permits the BMT and CBMT molecules to lie more flat on the surface. Full coverage can be restored by reimmersing the electrode in thiol solution. Monolayers formed from symmetric disulfides are exactly like those formed from the corresponding thiols. If the gold electrode is immersed for prolonged periods in d...
TL;DR: In this paper, the molecular orientation of an ordered monolayer of glycine adsorbed on Cu(110) has been studied using X-ray Photoelectron Spectroscopy (XPS), Near Edge Xray Absorption Fine Structure (NEXAFS), XPD, Low-Energy Electron Diffraction (LEED) and theoretical calculations.
TL;DR: In this article, periodic density-functional calculations have been performed for the molecular and dissociative chemisorption of NO on Pd and Rh(100) and (111) surfaces, with generalized gradient approximation exchange-correlation functionals.
Abstract: The efforts to reduce NOx pollutants have stimulated a large interest in the understanding of the elementary processes for NO transformation on transition metal surfaces. Periodic density-functional calculations have been performed for the molecular and dissociative chemisorption of NO on Pd and Rh(100) and (111) surfaces, with generalized gradient approximation exchange-correlation functionals. The periodic systems are modeled by two-dimensional palladium or rhodium slabs with frozen geometry, on which a NO, N, O, or (N+O) adlayer is set. On Pd and Rh(100) at a coverage of 0.5 monolayer (ML), the bridge site is the most stable one with respective binding energies of −1.54 and −2.18 eV. On the (111) surfaces, at a coverage of 0.33 ML, the threefold hollow sites are favored with binding energies of −2.0 eV for Pd(111) and −2.18 eV for Rh(111). For the dissociated structures, the mixed coadsorption of N and O is favored in most cases compared to separated domains. The chemisorption of NO, N, or O is stronge...
TL;DR: In this article, first principles electronic structure calculations have been used to study the structure, energetics and vibrational spectra of the chemisorption products of several unsaturated hydrocarbons on the Si(100)-(2×1) surface.
TL;DR: In this article, the adsorption and photooxidation of salicylic acid on dispersed TiO2 (Degussa P-25) particles were studied as a function of substrate concentration and pH.
Abstract: The adsorption and photooxidation of salicylic acid on dispersed TiO2 (Degussa P-25) particles was studied as a function of substrate concentration and pH. Salicylic acid chemisorbs at the particle interface, forming inner-sphere titanium(IV) salicylate surface complexes. The visible differential diffuse reflectance spectra of the surface complexes present a band, with maximum absorption at 420 nm, which is assigned to the internal ligand to metal charge-transfer transition. The surface excess of salicylic acid increases with decreasing pH and levels off around pKa1. At constant pH, the surface excess increases with the concentration of salicylic acid, the isotherm reflecting surface site heterogeneity. Photooxidation rates in air-saturated solutions, on the other hand, are independent of both pH and salicylic acid concentration, in the entire studied range. Chemisorption results are accounted for by a multisite surface complexation model in which two different surface titanium sites and three complexatio...
TL;DR: In this paper, a coulometric procedure enabling the reliable and accurate evaluation of saturated CO coverages, θ sat CO, on Pt-group transition-metal electrodes is outlined, and applied to CO adlayers on ordered low-index platinum, rhodium, and iridium surfaces in acidic aqueous media.
TL;DR: In this article, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and H2 and CO chemisorptions were used to characterize Ru/alumina catalysts.
Abstract: Ru/alumina catalysts (0.21–5.11 wt% Ru) were characterized using temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and H2 and CO chemisorptions. The transformations of cyclohexene were used as test reactions. The TPR data showed, for the catalysts calcined at 500°C, two peaks at ∼190°C and 223°C. The high temperature peak becomes quantitatively more important as the Ru content is increased. With the aid of XPS and H2 and CO chemisorption, the low temperature peak is associated with a well-dispersed ruthenium phase while the high temperature peak is related to the reduction of RuO2 species. As expected from the dispersion measurements, the latter decreases with increasing Ru contents, in agreement with the literature. The catalytic results are in line with the characterization studies, showing an increase in the activity for the hydrogenolysis reaction (formation of methane) over the hydrogenation–dehydrogenation reactions, as the Ru content is increased. The latter can be explained in terms of the structural requirements of the hydrogenolysis reaction reported previously.
TL;DR: In this paper, three high surface area graphites with similar textural characteristics, but differing in surface chemistry, have been used as carriers for the preparation of carbon-supported Pt and Ru catalysts.
Abstract: In a study of the preparation of carbon-supported Pt and Ru catalysts, three high surface area graphites with similar textural characteristics, but differing in surface chemistry, have been used as carriers. Four series of metallic catalysts (two based on Pt and two on Ru) have been prepared by using different metal precursors and preparation methods. The catalysts were characterized by temperature-programmed reduction, H2 and CO chemisorption and microcalorimetry of CO chemisorption. The achieved metallic dispersions mainly depend on the reduction-decomposition treatments and on specific interactions between the metal particles and surface defects at the graphite. Microcalorimetry of CO adsorption evidences that the presence of oxygen surface groups diminishes the metal–support interaction.
TL;DR: In this article, two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which has been introduced using both H 2 PtCl 6 in acid media and [Pt(NH 3 ) 4 ]Cl 2 in basic media.
Abstract: Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which has been introduced using both H 2 PtCl 6 in acid media and [Pt(NH 3 ) 4 ]Cl 2 in basic media. The catalysts have been characterized by H 2 chemisorption at room temperature (after different pre-treatments), temperature-programmed reduction (TPR) and temperature-programmed desorption of adsorbed hydrogen (H 2 -TPD), and their catalytic behavior in the gas-phase hydrogenation of benzene has been determined under differential conditions. TPD profiles of oxygen surface groups in fresh catalysts evidenced the support oxidation by H 2 PtCl 6 , with the occurrence of a CO evolution peak at low temperature (630 K). The presence of oxygen surface groups in the support favors the anchoring of [Pt(NH 3 ) 4 ] 2+ , but does not affect the amount of platinum retained by the support when H 2 PtCl 6 is used as metal precursor. TPR experiments have evidenced that the oxidized support hinders the reduction of the platinum precursor. The catalytic activities in the benzene hydrogenation reaction do not show a direct correlation with dispersion values obtained from hydrogen chemisorption, and it has been related to storage and mobility of hydrogen which is spilt over the support during the reduction treatments.
TL;DR: In this paper, the reaction of water vapor at 300 K and different water vapor pressures, p (H 2 O), was studied using Synchrotron-based photoemission spectroscopy and low-energy electron diffraction.
TL;DR: The results of parametric bench-scale tests investigating the removal of mercuric chloride and elemental mercury by activated carbon indicate that the adsorption capacity of a given sorbent is dependent on many factors, including the type of mercury being adsorbed, flue gas composition, and adsorptive temperature.
Abstract: The Electric Power Research Institute (EPRI) is conducting research to investigate mercury removal in utility flue gas using sorbents. Bench-scale and pilot-scale tests have been conducted to determine the abilities of different sor-bents to remove mercury in simulated and actual flue gas streams. Bench-scale tests have investigated the effects of various sorbent and flue gas parameters on sorbent performance. These data are being used to develop a theoretical model for predicting mercury removal by sorbents at different conditions. This paper describes the results of parametric bench-scale tests investigating the removal of mercuric chloride and elemental mercury by activated carbon. Results obtained to date indicate that the adsorption capacity of a given sorbent is dependent on many factors, including the type of mercury being adsorbed, flue gas composition, and adsorption temperature. These data provide insight into potential mercury adsorption mechanisms and suggest that the removal of mercu...
TL;DR: In this article, the authors used N 1s and O 1s photoelectron diffraction to determine the local geometry of glycine adsorbed on Cu(110) in an ordered (3 × 2) phase.
TL;DR: The core-level binding energies of simple unsaturated organic molecules bonded to the Si(001) surface have been investigated using X-ray photoelectron spectroscopy (XPS) using the Si 2p levels as an internal standard, the shifts in carbon and nitrogen levels were analyzed for a series of small unsaturated molecules, including cyclopentene, ethylene, acetylene, 3-pyrroline and pyrrolidine, adsorbed on the silicon surface.
TL;DR: The advantageous features of this strategy, which include ease of sample preparation, an internal reference plane for the detection of topographic changes, and the potential for regeneration and reuse, are demonstrated using rabbit IgG as an immobilized antigen and goat anti-rabbit IgGAs the complementary antibody.
Abstract: This paper combines the topographic imaging capability of the atomic force microscope (AFM) with a compositionally patterned array of immobilized antigenic rabbit IgG on gold as an approach to performing immunoassays. The substrates are composed of micrometer-sized domains of IgG that are covalently linked to a photolithographically patterned array of a monolayer-based coupling agent. The immobilized coupling agent, which is prepared by the chemisorption of dithiobis(succinimidyl undecanoate) on gold, is separated by micrometer-sized grids of a monolayer formed from octadecanethiol (ODT). The strong hydrophobicity of the ODT adlayer, combined with the addition of the surfactant Tween 80 to the buffer solution that is used in forming the antibody-antigen pairs, minimizes the nonspecific adsorption of proteinaceous materials to the grid regions. This minimization allows the grids to function as a reference plane for the AFM detection of the height increase when a complementary antibody-antigen pair is formed. The advantageous features of this strategy, which include ease of sample preparation, an internal reference plane for the detection of topographic changes, and the potential for regeneration and reuse, are demonstrated using rabbit IgG as an immobilized antigen and goat anti-rabbit IgG as the complementary antibody. The prospects for further miniaturization are discussed.
TL;DR: In this article, a method for increasing the lateral chain density in self-assembled monolayers (SAMs) of alkanethiols on polycrystalline gold was presented.
Abstract: We present a method for increasing the lateral chain density in self-assembled monolayers (SAMs) of alkanethiols on polycrystalline gold. This method relies on exposure of the alkanethiolate monolayers to mercury vapor and subsequent reimmersion into the thiol solution. Mercury adsorption on the gold surface induces a structural rearrangement in the alkanethiolate monolayers, as indicated by changes in dichroism in the Fourier transform infrared (FTIR) spectra, in line shape in the sum frequency generation (SFG) spectra, and in the macroscopic wetting behavior of the monolayers. X-ray photoelectron spectroscopy (XPS) data show that saturation of the thiolate samples with mercury occurs after 20−30 min of exposure to air saturated with mercury vapor. For 100 nm evaporated gold films a mercury bulk concentration of 14−16 atom % was determined by energy-dispersive X-ray analysis (EDX). Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) data indicate that after mercury adsorption the monolayers consist...