Showing papers on "Chemisorption published in 1992"
TL;DR: The Kinetic Theory of Gases as discussed by the authors describes the physical structure of surfaces and their properties, including surface curvature, surface tension, and surface mobility, as well as surface chemistry.
Abstract: SURFACE STRUCTURE, THERMODYNAMICS, AND MOBILITY. Atomic Structure of Surfaces. Electronic Structure of Surfaces. Surface Tension. Thermodynamics of One-Component Systems. Thermodynamics of Multicomponent Systems. Surface Mobility. GAS-SURFACE INTERACTIONS. The Kinetic Theory of Gases. Molecular Beam Formation. Gas Scattering. Adsorption-The Kinetic View. Physical Adsorption. Chemisorption. Surface Chemical Reactions. ENERGETIC PARTICLE-SURFACE INTERACTIONS. Electron-Surface Interactions. Ion-Surface Interactions. Photon-Surface Interactions. CRYSTAL GROWTH. Crystal Nucleation and Growth. Index.
464 citations
TL;DR: Nanocatalysis inspired by Enzymatic Cofactors inspired by Chemisorption Reference LNS-ARTICLE-1992-001 is reported on.
Abstract: Scanning-tunneling-microscopy observations on an Al(111) surface reveal that O adatoms at 300 K are practically immobile. Low-coverage overlayers formed by dissociative chemisorption of ${\mathrm{O}}_{2}$ consist essentially only of single isolated atoms rather than of pairs of adjacent atoms. Hence, upon dissociation, at least part of the chemisorption energy must be transformed into translational energy parallel to the surface which causes the two O atoms formed to separate from each other by at least 80 \AA{} before the excess energy is dissipated. The lifetime of these ``hot'' adatoms is estimated to be on the order of \ensuremath{\ge}1 ps.
281 citations
TL;DR: In this article, an attempt is made to study the mechanism of adsorption by using the concept of π-scale of potential as proposed by Antropov, and the potential of zero charge of mild steel is studied by two different techniques.
Abstract: Generally, aromatic amines are regarded as effective inhibitors for pickling and acid cleaning of mild steel in hydrochloric acid. Most previous studies advocate the view that the inhibition is a result of adsorption of the π-electron cloud of the aromatic ring on the iron and steel surface through vacant dπ orbital of iron. Later studies indicate a possible electrostatic adsorption or chemisorption due to synergistic action between halide ion and amine molecules as responsible for inhibition. In this paper, an attempt is made to study the mechanism of adsorption by using the concept of π-scale of potential as proposed by Antropov. The potential of zero charge (PZC) of mild steel is studied by two different techniques, and the mechanism of adsorption thus predicted has been found to corroborate the results of in situ Raman scattering study.
207 citations
TL;DR: In this article, it was shown that when CO is bound through carbon, its vibrational frequency increases with respect to the gas-phase value, and the positive Δω does not arise entirely from the field-dipole interaction but is due to the increase in Pauli repulsion occurring when the CO molecule vibrates in the presence of the surface wall.
Abstract: The interaction of CO with the MgO(100) surface has been investigated by means of all electron cluster model calculations. The CO molecule is bound on the Mg2+ site of MgO with a chemisorption energy of about 0.2 eV. The binding mechanism is electrostatic in nature and arises almost entirely from the interaction of the weak electric field generated by the ionic surface and the CO charge distribution, with negligible contributions from chemical effects as the CO σ donation. When CO is bound through carbon, its vibrational frequency increases with respect to the gas-phase value. This shift, Δ, has been analyzed and decomposed into the sum of different contributions. It is found that the positive Δω does not arise entirely from the field–dipole interaction but is due, in part, to the increase in Pauli repulsion occurring when the CO molecule vibrates in the presence of the surface “wall.” A stronger electrostatic interaction, bringing the CO adsorbate closer to the surface, increases this wall effect and results in a more pronounced positive ω shift. It is also found that the two CO orientations exhibit opposite shifts in ωe, thus, the two orientations can be distinguished, in principle, by IR spectroscopy. The analysis of our ab initio cluster wave functions gives a very different picture than the standard view of the metal–CO bond as arising from σ donation and π back donation.
200 citations
01 Mar 1992
TL;DR: In this paper, a double layer is formed on gold, for the UHV-prepared layer and evidence is found for the coordination of both amino and carboxyl groups to the surface, in addition to chemisorption through the thiol group.
Abstract: l -Cysteine adsorbates and multilayer films on gold and copper surfaces have been investigated by X-ray photoelectron spectroscopy. Both adsorbates, prepared by vapor deposition in UHV and prepared from solution, strongly indicate a dissociative chemisorption through the thiol group (−SH) on the metal surface. We suggest that an organized double layer is formed on gold, for the UHV-prepared layer. In the case of copper, evidence is found for the coordination of both amino and carboxyl groups to the surface, in addition to chemisorption through the thiol group. When l -cysteine is adsorbed from solution on copper, all of the thiol groups interact with copper ions, even in a 25-A-thick layer. This indicates copper ion diffusion and copper complex formation through the entire layer.
197 citations
TL;DR: In this article, the adsorption of ethylene on Si(100)-(2 × 1) has been studied in ultrahigh vacuum, and the activation energy difference for desorption and chemisorption from the precursor (Ed − Er), was found to be 2.9 kcal mol−1.
186 citations
TL;DR: In this paper, the adsorption and decomposition of acetylene on Si(100)-(2×1) have been studied in ultrahigh vacuum by Auger electron spectroscopy, temperature-programmed desorption, and changes in the partial pressure of a monolayer.
Abstract: The adsorption and decomposition of acetylene on Si(100)-(2×1) have been studied in ultrahigh vacuum by Auger electron spectroscopy, temperature-programmed desorption, and changes in the partial pressure of acetylene as measured by a quadrupole mass spectrometer during the formation of a monolayer. Acetylene was found to chemisorb onto Si(100)-(2×1) via a mobile precursor. The difference between the activation energy for desorption from the precursor and that for reaction from the precursor into the chemisorbed state was found to be (E d -E r )=1.9±0.6 kcal mol -1
155 citations
TL;DR: In this article, an active site consisting of coordinatively unsaturated cupric (Cu2+) ions in a square planar configuration is proposed to chemisorb NO molecules in the gem-dinitrosyl form.
Abstract: Cu-ZSM-5, a copper-containing zeolite, catalytically decomposes NO at temperatures below those of other catalysts. A mechanism is proposed which is based on active sites consisting of coordinatively unsaturated cupric (Cu2+) ions in a square planar configuration. These sites are posited to chemisorb NO molecules in the gem-dinitrosyl form. The pair of adsorbed NO molecules desorbs as N2 and O2. This mechanism accounts for the experimental behavior in chemisorption and decomposition without invoking a cyclical oxyreduction of the surface sites.
150 citations
TL;DR: In this article, the dissociative chemisorption of methane at an atop-atom site on a (111) surface of nickel is treated using a many-electron embedding theory to describe bonding, modeling the lattice as a 41-atom, three layer cluster.
Abstract: The dissociative chemisorption of methane at an atop‐atom site on a (111) surface of nickel is treated using a many‐electron embedding theory to describe bonding, modeling the lattice as a 41‐atom, three layer cluster. Ab initio valence orbital configuration interaction (multiple parent) calculations carried out on a local surface region permit an accurate description of bonding at the surface. Ni 3d orbitals are explicitly included on seven nickel atoms on the surface. The calculated activation energy of CH4 adsorbed at an atop Ni site to produce CH3 and H coadsorbed at separated threefold sites is 17 kcal/mol. The dissociation of CH4 to CH3(ads)+H (ads) is predicted to be 2.8 kcal/mol exothermic. The Ni 3d orbitals contribute to the bonding by directly mixing with methane C–H orbitals during the dissociation process and through a direct interaction of 3d9 and 3d10 configurations at the transition state. The dissociation pathway and the bonding properties of adsorbed CH4 and coadsorbed CH3 and H are disc...
148 citations
TL;DR: In this article, the electronic and geometric structure of TiO 2 supports are monitored during overlayer formation in the sub-monolayer and monolayer regimes, and the appearance of Ti 3+ features in XPS spectra is confirmed.
141 citations
TL;DR: In this article, the role of phenyl substituent groups in the formation of surface complexes at the surface of titanium dioxide semiconducting ceramic membranes is investigated with cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy.
Abstract: The role of phenyl substituent groups in the formation of surface complexes at the surface of titanium dioxide semiconducting ceramic membranes is investigated with cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. The CIR-FTIR study presented in this article allows for direct comparison between adsorption mechanisms derived from vibrational spectra at the semiconductor-liquid interface and surface structures influencing aqueous heterogeneous photochemical reactions. Therefore, chemisorption mechanisms we derived for benzoic acid and its substituted compounds could be used for the prediction of their photodegradation behavior. This IR investigation confirms that no adsorption is detectable on the rutile phase of TiO2, thus excluding the role of 5-fold coordinated Ti cations in the adsorption mechanisms. We observed that, for anatase surface, isolated carboxyl groups do not generate a favorable adsorption equilibrium (e.g., benzoic acid). It is proposed that amino and hydroxyl groups substituted in ortho position to a carboxyl group (e.g., salicylic, 3-chlorosalicylic, and anthranilic acids) may lead to a mononuclear bidentate coordination complex with 4-fold coordinated surface titanium cations. The higher adsorption level observed for phthalic acid is interpreted as due to its possibility of adsorbing on a greater number of anatase surface sites, by forming two different surface complexes, involving one or both carboxyl groups. A relationship between change in vibrational spectra of the carboxyl group, for substituted benzoic derivatives, and acidic dissociation constants is presented.
TL;DR: In this paper, it was shown that at room temperature, in the presence of highly dispersed rhodium, ceria chemisorbs large amounts of hydrogen, which leads to the reduction of ceria to an extent of 21% of the total amount of cerium ions present in the sample.
TL;DR: In this article, a modified Langmuir-Hinshelwood model with competitive adsorption between p-chloronitrobenzene (CNB) and hydrogen has been studied, in methanol suspension, at 303 K and atmospheric pressure, over a series of Pt/Al2O3 and PtM/Al 2O3 catalysts.
TL;DR: In this article, a model of promoter action is proposed for ammonia synthesis using a chlorine-free Ru/Al2O3 catalyst, and it is shown that small amounts of lanthanide nitrates (M/Ru = 1) were as effective as a much greater amount of CsNO3 (CS/RU = 10).
TL;DR: The results indicate that the Pd(3d 5/2 ) binding energy for a monolayer (ML) of Pd on Re(0001) and Ru(000) is perturbed by +0.60 and -0.30 eV, respectively, from that of the surface atoms of PD(100).
Abstract: The nature of the electronic and chemical properties of ultrathin Pd films on Re(0001) and Ru(0001) has been studied using x-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and CO chemisorption. The results indicate that the Pd(3${\mathit{d}}_{5/2}$) binding energy for a monolayer (ML) of Pd on Re(0001) and Ru(0001) is perturbed by +0.60 and +0.30 eV, respectively, from that of the surface atoms of Pd(100). These electronic perturbations induce large changes in the chemical properties of the Pd films. TPD results indicate that the desorption temperature of CO from 1 ML of Pd on Re(0001) and Ru(0001) is \ensuremath{\sim}120 K lower than the corresponding desorption temperature from Pd(100). The XPS and CO-TPD data indicate that Pd transfers charge to the Re and Ru substrates, becoming electron deficient and less efficient at \ensuremath{\pi} backdonation toward CO. By comparison of these results with those reported previously for Pd, Ni, and Cu adlayers, a correlation is observed among the electronic perturbations of the adlayers, the cohesive metal-substrate bond strength, the ability of the film to chemisorb CO, and the CO-induced shift in the metal core-level binding energy. In general, the results indicate that the formation of a metal-metal bond at a surface leads to a gain of electron density by the element initially having the greater fraction of empty states in its valence band. This behavior is completely contrary to that seen in bulk alloys, likely a consequence of the anisotropic character of a surface that changes the relative electronegativities of the metal atoms. On the basis of these results, a qualitative scale of surface electronegativities is developed, showing trends that are very different from those found in three-dimensional bulk alloys.
TL;DR: Duriez et al. as discussed by the authors measured the adsorption-desorption kinetics of CO on Pd clusters, epitaxially grown on MgO(100).
TL;DR: In this article, the authors investigated the formation of a dative σ-bond with the surface of the MgO(100) surface and found that the formation is largely due to electrostatic effects.
TL;DR: In this article, the interaction of atomic hydrogen with halogen-terminated Si(100) surfaces was studied by Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) Mass Spectroscopy.
Abstract: : The interaction of atomic hydrogen with halogen-terminated Si(100) surfaces was studied by Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) mass spectroscopy. Efficient removal of surface halogen has been observed when the halogen-terminated S1(100) surface was exposed to atomic hydrogen at a substrate temperature, 630 K. The reaction rate constants for halogen extraction on the S1(100) surface follow the trend kI greater than kBr greater than kCl. In addition, the halogen extraction kinetics are found to be first order in both the surface coverage of halogen and in the atomic hydrogen flux. Studies of the temperature dependence of the halogen extraction rate show the activation energies for the extraction of Cl and Br are 2.1 and 1.6 kcal mol-1, respectively. The extremely low activation energy for the reaction demonstrates that the H-extraction process follows an Eley-Rideal reaction mechanism where the surface reaction is mainly driven by the high internal energy of incident atomic hydrogen instead of thermal excitation from the S1(100) solid surface.
TL;DR: In this paper, the authors show that near-ultraviolet (UV) illumination in the presence of TCE vapor leads to desorption of molecular water and subsequent formation of several adsorbed hydrocarbon intermediates and carbon dioxide.
TL;DR: In this paper, the chemisorption and thermal decomposition of ethyl iodide on Pt(111) have been studied by reflection-absorption infrared spectroscopy (RAIRS).
TL;DR: In this article, the decomposition of CH4 on Cu(100 has been studied by XPS in the temperature range 800-1000 K and the activation energy of the chemisorption probability on the clean surface (the initial sticking coefficient) is about 201 kJ/mol.
TL;DR: In this paper, a poorly ordered p(2 × 1) surface structure formed by pre-adsorbed oxygen on Cu(311) at about 0.4 ML oxygen and increasing the oxygen coverage further enhances surface disorder.
TL;DR: In this article, the growth mode appears to be layer-by-layer for the first few layers, as indicated by Auger and ion scattering spectroscopies, and a model is proposed for both overlayers consisting of an FeO(111) bilayer of Fe2+ and O2−.
TL;DR: In this article, the intrinsic activity of molybdenum carbides in comparison with known catalysts was measured by studying selective chemisorption of CO and H{sub 2} in much more detail than was done in earlier preliminary work.
Abstract: Molybdenum carbides is being considered as a potential replacement for noble metals in some catalytic processes Such catalysts have demonstrated performance in hydrocarbon synthesis from CO and H{sub 2}, hydrogenation of benzene, alcohol synthesis, etc This paper reports work to measure the intrinsic activity of this material in comparison with known catalysts The work is done by studying selective chemisorption of CO and H{sub 2} in much more detail than was done in earlier preliminary work
TL;DR: In this paper, the authors investigated the kinetics and mechanism of graphite gasification by CO2 and H2O catalyzed by five alkali and alkaline earth metal catalysts.
TL;DR: In this paper, the first monolayer of the organic coating should be bonded by chemical bonds to the substrate in order to increase the chemical and electrochemical stability of metal/polymer composite materials.
TL;DR: In this article, the authors investigated the reactions of atomic oxygen with the (100) and (111) surfaces of silicon using supersonic molecular beam techniques, X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering spectroscope (ISS).
01 Jan 1992
TL;DR: In this paper, a general energy decomposition scheme for the study of metal-ligand interactions in complexes clusters and solids is proposed for homogeneous and heterogeneous catalysis in transition metal systems.
Abstract: Ligands on clusters - adsorbates on surfaces the chemistry of transition metal clusters surface science studies of molecular adsorbates on solid surfaces - a series of case studies concepts in heterogeneous catalysis electronic structure theory for transition metal systems - a survey selectivity in catalysis by metals and alloys metal-CO interactions - well-defined surfaces and supported particles linear semibridging carbonyls 5 the structure and bonding of the chromium cyclopentadienyl dicarbonyl dimer carbon dioxide organometallic chemistry - theoretical developments quantum chemical models of chemisorption on metal surfaces catalytic reactions of transition metal clusters and surfaces from ab initio theory reactivity and electronic structure of organometallic radicals density functional theory - principles and applications to metal-ligand interactions density functional model calculations for homogeneous and heterogenous catalysis a general energy decomposition scheme for the study of metal-ligand interactions in complexes clusters and solids physiochemical characterization of novel polymeric copper complexes with long-chain aliphatic diamines.
TL;DR: Dimers of rhodium (Rh) and palladium (Pd) catalysts were investigated during a conversion reaction with carbon monoxide (CO), and the hydrogenation of CO on supported Rh particles produces a variety of compounds such as hydrocarbons, alcohols, aldehydes, and acids.
Abstract: Dimers of rhodium (Rh) and palladium (Pd) catalysts were investigated during a conversion reaction with carbon monoxide (CO). The hydrogenation of CO on supported Rh particles produces a variety of compounds such as hydrocarbons, alcohols, aldehydes, and acids. The chemisorption of CO is different in these two metals, and this report discusses bonding differences that may contribute to this outcome. 78 refs., 4 tabs.