Showing papers on "Chemisorption published in 1969"

Low‐Energy Electron‐Diffraction Studies of the Adsorption of Unsaturated Hydrocarbons and Carbon Monoxide on the Platinum (111) and (100) Single‐Crystal Surfaces

Abstract: The interaction of simple aliphatic hydrocarbons and carbon monoxide with Pt(111) and Pt(100) surfaces, at gas pressures ≤ 1 × 10−7 torr, has been studied using low‐energy electron diffraction (LEED), mass spectrometry, flash desorption, and work‐function (φ) measurements. The Pt(111) substrate was characterized by a (1 × 1) diffraction pattern while a (5 × 1) surface structure was visible on Pt(100). In contrast to the saturated hydrocarbons, all the other gases used (CO, C2H2, C2H4, C3H6, 1,3‐butadiene and the isomeric butenes) were readily chemisorbed on both substrates. Relatively large decreases in φ resulted from the chemisorption of the unsaturated hydrocarbons while a small increase in φ was measured due to the adsorption of CO. A (2 × 2) surface structure was produced on the (111) face by all of the unsaturated hydrocarbons studied, with the exception of isobutylene which exhibited a larger unit mesh. Although C2H2 and C2H4 produced a C(2 × 2) structure on the (100) face of platinum, the adsorpti...

Chemisorption on Rhenium: N2 and CO

Abstract: The chemisorption of N2 and CO on polycrystalline Re has been studied using flash desorption. A number of binding states have been identified and their binding energies have been estimated kinetically. Isotopic mixing between chemisorbed species has been observed for the β‐N2 and β‐CO states on Re; there appears to be no evidence for dissociation of β‐CO. The γ‐N2 and two α‐CO states on Re desorb without isotopic mixing. In general, the distribution and properties of binding states for N2 and CO on Re are remarkably similar to those found for these adsorbates on W. An enhancement in nitrogen adsorption on Re occurs upon electron impact (150 eV) on N2(g). A new set of strongly bound states are produced which are distinct from the β‐N2 states populated by adsorption of ground‐state N2(g). A comparison of the sticking coefficients for N2 and CO on Re is made, using two independent methods (uptake and isotopic mixing) over a wide temperature range. The sticking coefficient for N2 on Re decreases markedly with increasing temperature; for CO on Re, there is little effect of temperature on the sticking coefficient. A discussion is presented of migration‐limited bimolecular kinetics at elevated temperatures in the chemisorbed layer.

Nature of the chemisorption bond on semiconductor surfaces

Abstract: Results obtained by various quantum-mechanical approaches in studying localized states on crystal surfaces are summarized and discussed. The one- and many-electron aspects of the problem are compared and shown to lead to similar results. Emphasis is laid upon localized chemisorption states on intrinsic semiconductors. The problem of the calculation of chemisorption heat on solid surfaces is also mentioned.

Chemisorption of copper atoms on platinized platinum in sulphuric acid solution

Abstract: The cathodic formation and the anodic removal of chemisorbed layers of copper atoms was studied at room temperature on platinized platinum in 0.5 MH2SO4+X M CuSO4 . 5 H2O (3.10–4⩽X⩽ 10–1) at potentials positive to that of the reversible copper electrode in the respective solution. The initial rate of layer formation is controlled by mass transport processes and a slow step in the discharge reactions at small bulk concentrations (10–3 M) of Cu2+ions. The maximum number of adsorption sites that are covered by Cuad at large bulk concentrations decreases with potential. It is equal to the number of sites for hydrogen adsorption at 0.3 V and to zero at 0.8 V. One Cuad covers one adsorption site for Had in a first approximation. When the coverage with copper atoms is about one half, the effect of Cuad on hydrogen adsorption can be described as repulsive between 0.2 and 0.3 V and as attractive between 0 and 0.2 V.

Surface reactivity of magnesium oxide doped with manganese: an e.s.r. and chemisorption study

Abstract: At 600°C hydrogen and oxygen are adsorbed on magnesium oxide doped with manganese to an extent which is dependent on the manganese concentration. E.s.r. studies indicate that adsorption of hydrogen results in a reduction of higher valence states to Mn2+, whereas adsorption of oxygen converts Mn2+ into Mn3+ and Mn4+, which concentrate at the oxide surface. The stoichiometry and mechanism of these processes have been investigated in powders of small (∼100 A) and large (∼600 A) average particle sizes. At 20°C the adsorption of hydrogen is little affected by manganese impurity whereas the adsorptions of oxygen is directly proportional to the manganese concentration. These adsorptions are weak forms of chemisotorption and do not appear to involve charge transfer. The e.s.r. spectra of Mn2+ in the small particles of MgO are interpreted in terms of a D term in the Hamiltonian and the presence of this axial component in the normally octahedral environment of Mn2+ is thought to arise from the proximity of the surface.

Corrosion of Platinum Metals and Chemisorption

Abstract: As the theoretical corrosion (potential-pH) diagram shows, palladium metal is thermodynamically stable at all pH's in the presence of aqueous solutions free from strong oxidizing, reducing, or com-plexing agents [1]. In practice, palladium is acted upon by water only at high temperatures [2] and it does not tarnish when exposed to moist air. Moreover, at ordinary temperatures this metal is not attacked by nonoxidizing acidic solutions.

Mechanism and kinetics of interaction between gaseous oxygen and nickel oxide surfaces

Abstract: The interaction between gaseous oxygen and the surface of pure nickel oxide and NiO doped with Li2O was studied by means of work function measurements. It was observed that at low oxygen pressures in measurements carried out with a constant amount of the gas in the reaction chamber, rather than carried out at constant pressure, at the temperatures corresponding to the adsorption equilibrium, the work function initially increased and then decreased. It was concluded that this complex character of the observed work function changes versus time is due to the superimposition of two parallel effects, i.e., charging of the NiO surface during oxygen chemisorption and simultaneous discharging of this surface by diffusion of ions from the bulk. On the basis of the electric model of the NiO surface covered with adsorbed oxygen, a quantitative interpretation of the above processes was proposed and a kinetic equation was given. The proposed kinetic equation was solved with the aid of an analog computer, and good agreement between the experimental curves and the kinetic equation was obtained.