Showing papers on "Chemisorption published in 1979"
TL;DR: In this paper, the location of a half monolayer of ordered hydrogen adatoms on Ni(111) has been analyzed by Low-Energy Electron Diffraction (LEED), Thermal Desorption Spectroscopy (TDS), and Work Function (Δφ) measurements.
Abstract: The location of a half monolayer of ordered hydrogen adatoms on Ni(111) has been analyzed by Low‐Energy Electron Diffraction (LEED), Thermal Desorption Spectroscopy (TDS), and Work Function (Δφ) measurements. It is found that the hydrogen atoms are arranged in an overlayer of graphitic structure with a (2×2) unit cell with respect to the substrate unit cell. In the ordered regions, the hydrogen adatoms occupy both types of three fold hollow sites without a detectable difference in the Ni–H bond lengths between the two sites. The Ni–H bond length is found to be 1.84±0.06 A, corresponding to an overlayer‐substrate spacing of 1.15±0.1 A. The relation between this structure and its observed order–disorder phase diagram as a function of temperature and hydrogen coverage is discussed. The disorder is discussed in detail, and a novel ’’atomic band structure’’ interpretation is given.
410 citations
TL;DR: In this paper, the authors defined the heat of adsorption as the energy needed to break the MX2 bond and defined ΔHads as the amount of energy required to do so.
Abstract: One of the important physical-chemical properties that characterizes the interaction of solid surfaces with gases is the bond energy of the adsorbed species. The determination of the bond energy is usually performed indirectly by measuring the heat of adsorption (or heat of desorption) of the gas [1, 2], In order to define the heat of adsorption, let us consider the chemisorption of a diatomic molecule, X2, onto a site on a uniform solid surface, M. The molecule may adsorb without dissociation to form MX2. M represents the adsorption site where bonding occurs to a cluster of atoms or to a single atom. In this circumstance, the heat of adsorption, ΔHads, is defined as the energy needed to break the MX2 bond:
306 citations
TL;DR: In this paper, the stable surface species formed from the chemisorption of acetylene (C2H2) or ethylene (c2H4) on the Pt(111) surface (T∼300-350 K) has been studied by a low-energy electron diffraction intensity analysis.
Abstract: The stable surface species formed from the chemisorption of acetylene (C2H2) or ethylene (C2H4) on the Pt(111) surface (T∼300–350 K) has been studied by a low‐energy electron diffraction intensity analysis. High resolution electron energy loss spectra reported by Ibach et al. have been interpreted by comparison to infrared data on relevant model compounds. The surface species most consistent with these studies is ethylidyne ( C–CH3). The species is coordinated to a threefold surface site with the C–C axis normal to the surface within an uncertainty of ∼15°. A saturated C–C bond length of 1.50±0.05 A and three equivalent Pt–C bond lengths of 2.00±0.05 A are determined by the LEED analysis and are consistent with the reported structures of ethylidyne in organometallic clusters. The ethylidyne group forms readily upon exposure of C2H4 to the Pt(111) surface at T∼300 K with the loss of one hydrogen atom per ethylene. The complete conversion of C2H2 to ethylidyne requires the presence of hydrogen atoms and pro...
284 citations
TL;DR: In this paper, the authors studied the chemisorption of CO on Cu(111) at low temperatures by reflection-absorption infrared spectroscopy, LEED and surface potential measurements.
283 citations
TL;DR: In this article, the chemisorption and decomposition of formic acid on a copper (100) surface has been studied with high resolution electron energy loss spectroscopy, and two molecular orientations of formate have been resolved at different temperatures.
232 citations
TL;DR: In this paper, the activation energy for first-order CO desorption is 31.6 kcal/mole (νd = 1013.6s−1) in the limit of zero coverage, and as CO coverage increases, a (√ 3 ×√3)R30u overlayer is produced and then destroyed with subsequent formation of an overlayer yielding a 2 × 2) LEED pattern in the full coverage limit.
212 citations
TL;DR: In this paper, a model study on the promotor action of K in the synthesis of ammonia on iron catalysts was performed by studying the influence of preadsorbed potassium on the rate of dissociative nitrogen chemisorption on a Fe(100) single crystal surface.
188 citations
IBM1
TL;DR: In this paper, a methoxy species (CH3O) was identified as a quasi-stable surface intermediate during the thermal decomposition of chemisorbed methanol.
179 citations
176 citations
TL;DR: The chemisorption of H2 on the (111) surface of Rh has been studied using thermal desorption mass spectrometry and low-energy electron diffraction as discussed by the authors.
TL;DR: In this paper, the chemisorption of NO on a Pt(100) single crystal surface at 140 and 300 K was investigated by high resolution electron energy loss spectroscopy, combined with Auger and LEED.
Abstract: The chemisorption of NO on a Pt(100) single crystal surface at 140 and 300 K was investigated by high resolution electron energy loss spectroscopy, combined with Auger electron spectroscopy and LEED. Chemisorption of NO was predominantly molecular. The unreconstructed Pt(100)−1×1 surface was characterized by a single NO stretch frequency at 1615 cm−1 and two low frequency vibrations at 230 and 380 cm−1. These latter modes are likely to represent the Pt–NO stretch and Pt–N–O bending vibrations, respectively. The adsorbed molecule has therefore Cs symmetry in this case and is bent with respect to the surface normal. Low coverage NO adsorption at 140 K on the reconstructed Pt(100)−5×20 surface gave rise to three frequencies at 1690, 465, and 310 cm−1. Thus NO is also adsorbed in a bent configuration on this surface. At higher coverage an additional NO stretch frequency at 1790 cm−1 indicated a second adsorption site. Low frequency modes could not be clearly resoled for this species. NO adsorption on the same...
TL;DR: In this paper, a conceptual model for the photon emission observed during chemisorption on metals was developed and extended to electron emission, with estimated molecular velocities and electronic structure in the region slightly outside the surface, the probability of an electronically excited intermediate state is calculated.
TL;DR: In this article, the effects of preoxidation on catalytic rates and selectivity were found to be sensitive to the structure of the platinum surface, kink sites playing a particularly active role in the enhancement of dehydrogenation and hydrogenation activity by strongly bound oxygen.
TL;DR: In this article, the changes in the ellipsometric angles Δ and ψ per oxygen atom upon adsorption and removal of oxygen depend on the coverage θ, the temperature and on the azimuth of the plane of incidence of the light beam.
TL;DR: In this paper, it was found that linear Ag+3 clusters are formed upon activation, the ends of which constitute chemisorption sites for hydrogen and oxygen, while one molecule of carbon monoxide was chemisorcised per Ag ion available in the supercage.
Abstract: Carbon monoxide, oxygen and hydrogen were found to be chemisorbed on dehydrated AgA zeolites. This was investigated in detail using volumetric sorption and temperature programmed desorption techniques. Also i.r. and mass spectrometry were used to characterize the solid and the desorbed molecules.It was found that as a result of an auto-reductive process, colour centres are created upon degassing of the zeolite. These centres sorb hydrogen and oxygen dissociatively, while one molecule of carbon monoxide was chemisorbed per Ag ion available in the supercage. It is proposed that linear Ag+3 clusters are formed upon activation, the ends of which constitute chemisorption sites for hydrogen and oxygen.
TL;DR: In this paper, the ESDIAD results for CO confirm this orientation; for all CO coverages in the temperature range 90 K to ~ 350 K, the angular distributions of O+ and CO+ ESD ions are centered about the surface normal.
TL;DR: In this article, the infrared spectrum of CO chemisorbed on alumina-supported rh surfaces has been studied following chemicalisorption at cryogenic temperatures, and it has been found that the species Rh(CO)2, formed on isolated rh sites, is produced rapidly via an activated chemisorsorption process above ∼200 K.
Abstract: The infrared spectrum of CO chemisorbed on alumina‐supported Rh surfaces has been studied following chemisorption at cryogenic temperatures. Major differences are observed in the distribution and spectroscopic character of chemisorbed CO species produced at low temperatures (110–170 K) compared to chemisorbed CO species produced on Rh at 295 K. It has been found that the species Rh(CO)2, formed on isolated Rh sites, is produced rapidly via an activated chemisorption process above ∼200 K. On more ’’crystalline’’ Rhx sites, containing chemisorbed CO, an activated CO adsorbate‐conversion process has been detected in which ?CO decreases by ∼50 cm−1 on warming the adsorbed layer above ∼265 K. Isotopic exchange between 13CO(g) and 12CO(ads) has been shown to occur rapidly at low temperature (∼200 K) for Rh(CO)2 species, whereas Rhx(CO) species exchange rapidly only at higher temperatures (≳250 K). These results, taken together, serve to confirm a model in which isolated Rh sites coexist on the alumina support w...
TL;DR: In this paper, lock-in and wave-form analyses of scattered H 2 + D 2 mixed beams were performed and it was shown that equilibrium between adsorbed hydrogen and deuterium can be reached rapidly at temperatures above 300 K.
TL;DR: The thermal stability of a monolayer catalyst is related to the parameter z/a, i.e., the ratio of the carrier cation charge to the sum of ionic radii of carrier cations and oxide anion.
Abstract: Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V2O3(OH)4. Using Al2O3, Cr2O3, TiO2, CeO2 and ZrO2, catalysts with an approximately complete monomolecular layer of vanadium(V) oxide on the carrier oxides can be prepared, if temperature is not too high. Divalent metal oxides like CdO and ZnO may already form threedimensional surface vanadates at moderate temperature.
The thermal stability of a monolayer catalyst is related to the parameter z/a, i. e. the ratio of the carrier cation charge to the sum of ionic radii of carrier cation and oxide anion. Thus, monolayer catalysts will be thermally stable only under the condition that z/a is not too high (aggregated catalyst) nor too small (ternary compound formation).
TL;DR: In this article, the room temperature adsorption of pyridine on η-Al2O3 dehydrated at several temperatures in the 25-700°C range has been studied by i.r. spectroscopy, u.v.-vis reflectance spectrograph and microgravimetry.
Abstract: The room temperature adsorption of pyridine on η-Al2O3 dehydrated at several temperatures in the 25–700°C range has been studied by i.r. spectroscopy, u.v.-vis reflectance spectroscopy and microgravimetry.Several species are formed that can be identified on the basis of the spectroscopic features of the 8a ring mode, whereas the 8b mode, which is common to all species, yields the total amount adsorbed. Quantitative interpretation of the spectral data is carried out using a computer program.The adsorbed species are interpreted as follows: a liquid-like physisorbed species, a species H bonded to surface OH groups through the nitrogen lone pair and three Lewis coordinated species. The latter are assigned to purely octahedral, tetrahedral–octahedral and purely tetrahedral cationic sites, respectively.The reactions occurring upon Py desorption above 400°C are discussed and a different interpretation is given to that in the literature.
IBM1
TL;DR: In this article, a combination of temperature programmed thermal desorption spectroscopy and UV photo-emission spectrograms was used to investigate the chemisorption and reaction of acetylene and ethylene with Pt(111) at T ∼ 100K and T ∼ 300K, respectively.
TL;DR: In this article, an electronic mechanism for energy dissipation was proposed to account for the loss in adsorbate kinetic energy necessary for the trapping of an adorbate in the surface potential well.
TL;DR: In this article, the interaction of NH3 with a Fe(110) surface was studied by means of LEED, AES, UPS, work function and thermal desorption measurements.
TL;DR: In this article, at 300 K CO dosing of a hydrogen-covered surface leads to displacement of the latter with an efficiency of ~0.7, and the surface saturates at a coverage of 0.1.
TL;DR: In this article, high-resolution electron energy loss spectroscopy (EELS) was used to investigate the Vibrational excitations of oxygen and sulphur chemisorbed on Ni(100) in the consecutive p(2 × 2) and c(2× 2) structures.
TL;DR: In this paper, the effects of the substrate pseudopotential lattice have been included by first order perturbation theory, and an improved method, namely inclusion of part of the pseudopotentials in a self-consistent way and only the remainder in perturbing theory, has also been used.
TL;DR: In this article, a (√7 × √7) R 10.9° structure for the Ag(111)-S system has been shown to have an essentially constant sticking probability of unity up to the completion of the first layer of S atoms.