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Item Cooperative Interactions and Two-dimensional Ordering in the Adsorption of HBr on KBr(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (06), 1981) Harrison, Lionel G; Koga, Yoshikata; Lassau, TroyAdsorption isotherms of HBr gas on high surface area KBr have markedly non-ideal shapes. These are analysed using a two-layer model with repulsive interactions between molecules in the first layer. An earlier report from this laboratory of a transition in the surface layer at 20 °C, induced by adsorption, is confirmed by these data. Likewise, an apparent restriction of first-layer adsorption to no more than 25% coverage seems to correlate with the previous report from this laboratory that a ‘two-dimensional compound’ K4Br3Cl is formed in surfaces partly exchanged with HCl. Heat of adsorption is 48.5 kJ mol–1(below transition) and 30.5 kJ mol–1(above transition); mean-field repulsion constant C is ca. 40 kJ mol–1; the transition has ΔHt= 18.0 kJ mol–1 and ΔSt= 59.0 J mol–1 K–1. The remarkably large magnitudes of some of these quantities are discussed in terms of a model for adsorption involving normal weak hydrogen bonding plus additional electrostatic interactions between the Br of adsorbed HBr and adjacent K+ ions. Thereby, interactions between admolecules become intermediate-range, rather than nearest neighbour, averaging C/12 ≈ 3–4 kJ mol–1.Item Adsorption of Butenes on NaY and Dehydroxylated Y Zeolites Studies by Infrared Spectroscopy(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (06), 1981) Datka, JerzyButene molecules adsorbed on NaY and dehydroxylated Y zeolites are bonded to electrophilic acid sites (Na+ ions or Lewis-acid sites) by their π electrons. The interaction of butene molecules with Lewis-acid sites results in an increase in the extinction coefficient of the band for the antisymmetric stretching vibration of the CH3 group thus indicating an increased polarization of the C—H bond. The rates of desorption of the butenes from NaY or dehydroxylated zeolites increase in the sequence but-1-ene < cis-but-2-ene < trans-but-2-ene. These differences are explained by considering the steric factor. At low pressures the maximum butene content in Y zeolites is 3 molecules per supercage.Item Adsorption of Carbon Monoxide on Copper (100) Studied by Photoelectron Spectroscopy and Low Energy Electron Diffraction(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74(3), 1978) Isa, Saadoon A.; Joyner, Richard W.; Roberts, M. WynBy combining u.v. and X-ray photoelectron spectroscopy with low energy electron diffraction, Cu(100) has been shown to adsorb carbon monoxide at 295 K. Adsorption, although molecular, has distinctly different spectroscopic characteristics from adsorption at 80 K. The oxygen (1s) binding energy is 1.3 eV lower at 295 K than at 80 K, the carbon 1s binding energy is also lower. The sticking probability is ∼10–6 at 295 K although close to unity at 80 K, and the energy of desorption is greater for the room temperature state. The LEED pattern, (√2 ×√2)R45° is the same as observed at 80 K (for θ < 0.5) but the maximum coverage is substantially smaller at 295 K (θ∼ 0.3) and the diffraction spots more diffuse. At 80 K the photoelectron spectroscopy and LEED data are similar to those observed previously. Changes in the u.v. induced spectra with increasing CO coverage are shown to reflect the onset of LEED “compression structures” rather than the presence of two adsorbed phases of carbon monoxide. We suggest that the existence of two distinct types of CO bonding on copper (100), (at 295 and 80 K) is a consequence of the molecule acting more as an electron acceptor, (“COδ–”) at 295 K and more like an electron donor, (“COδ+”) at 80 K. The presence of a chemisorption level 1.5 eV below the Fermi edge, i.e. in the s-band region of the spectrum, is interpreted as being due to reorganisation of metal s and d electrons which is in keeping with the transition metal-like characteristics of the adsorption at 295 K.Item Adsorption/absorption characteristics of caesium on oxidised stainless steel(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (06), 1978) Woolley, Robert L.The transitions between gas, adsorbed state and absorbed state have been studied for the case of caesium deposited on oxidised stainless steel. The theoretical discussion takes account of detailed properties of the surface monolayer. Experimental measurements give results whose form is consistent with the theory, and enable the appropriate materials parameters to be deduced.Item Effects of Ionisation on Adsorption from Solution(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Rendall, Henry M; Smith, Alec LThe adsorption of γ-picoline (4-methyl pyridine) at the silica–water interface, as a function of pH, is reported. A general model for the adsorption is developed, which allows for the possibility that the ionised (HPic+) and the neutral (Pic) forms of the molecule may both adsorb. For the limit of zero coverage, explicit expressions are derived which give a simultaneous fit of adsorption and electrokinetic measurements, and the model is extended to consider the complete adsorption isotherms. The magnitudes of the initial slopes of the isotherms, and the occurrence and position of a maximum in the adsorption with pH, are explained. The two forms of the picoline molecule have specific adsorption potentials of ∼–4 kT, with the neutral molecule slightly the more strongly adsorbed by ∼ 0.3 kT.Item Heat Capacity of the H2O/KNaX Zeolite Adsorption System(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Berezin, G. I.; Kiselev, A. V.; Sinitsyn, V. A.The heat capacity of the H2O/KNaX zeolite system has been measured at 34°C for various amounts of adsorption. The dependence of measured heat capacity of this system and calculated average molar heat capacity of adsorbate on the amount of adsorption passes through two distinct maxima. These maxima correspond to previously obtained waves in the plot of the heat of adsorption of water against the amount of adsorption for the same H2O/KNaX zeolite system. The maxima are due mainly to the contribution to the heat capacity of the heat of transfer of a part of the water molecules from the adsorption sites with higher heat of adsorption to those with lower heat of adsorption. The thermal stability of different water associates in zeolite pores has been investigated. The differential heat capacities of adsorbed water were calculated and the changes in the heat of adsorption of water when the temperature of the system was increased were determined. The results show that with increasing temperature there is a smoothing out of the waves produced in the plot of the differential heat of adsorption as the function of the amount of water adsorbed.Item Effect of silica surface dehydroxylation on adsorption of aromatic hydrocarbons from solution in n-alkanes(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Eltekov, Yu. A.; Khopina, V. V.; Kiselev, A. V.The adsorption of a series of aromatic hydrocarbons from solution in saturated hydrocarbons on hydroxylated and dehydroxylated silica surface has been investigated. Dehydroxylation of silica surface sharply diminishes the adsorption of aromatic hydrocarbons. Since the molecules of aromatic hydrocarbons on the hydroxylated silica are oriented parallel to the surface, the influence on adsorption of the size of molecules at the same orientation was investigated and distribution functions for several systems were determined. The equilibrium constants and the activity coefficients of surface benzene + n-hexane phases on hydroxylated and dehydroxylated silica and on graphitized carbon black surfaces have been calculated.Item Adsorption of Krypton on Alkali Halide Crystals: Part 1.—Theory(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (5), 1972) Takaishi, T.The adsorption of krypton on alkali halide crystals with the NaCl-type structure has been studied theoretically in order to analyze detailed experimental data given in a succeeding paper. Emphasis was placed on the mutual interaction between adsorbates, perturbed by the solid adsorbent (the third body effect). Changes of lateral vibrational state of the adsorbed krypton with coverage were taken into consideration in deriving an adsorption isotherm. An analysis is given of the third body effect in the localized adsorption model, and an equation derived which correlates the third body effect with the surface electric field. Using this equation, one can estimate the order of magnitude of the field strength, and, in favourable cases, verify the existence of the distortion of the surface lattice postulated by Benson and coworkers.Item Adsorption and Incorporation on Copper(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (8), 1972) Saleh, J MThe interaction of H2S, H2Sc, AsH3, HC1, SO2, CS2 and N2O with evaporated films of copper has been studied in the temperature range -80 to 250 C. Weak reversible adsorption of CS> and SO2, and mainly dissociative chemisorption of H2S, H2Sc, AsH3 and HC1 took place at -80 C. The extent of N2O adsorption on a Cu film at this temperature was negligibly small. The completion of the surface layer on a Cu film by either H2S, H2Se or AsH3 at temperatures > - 80 C was followed by the formation of bulk compounds and the process was accompanied by H2 evolution ; the activation energies of the incorporation processes were estimated from the rates of adsorption at different temperatures but virtually the same surface coverage. Dissociative chemisorption of N2O on Cu film above 30°C was very slow and proceeded to only a limited extent. Cu did not chemisorb CS2, SO2 or HC1 at any temperature in the range 30 to 250 C. The latter four gases were circulated over a heated W filament before reaction with the Cu film. The rate of uptake of the gas was a function of its pressure and the temperature of both the Cu film and the W filament. Activation energies were determined from the rates of adsorption at different temperatures either of the Cu film or of the W filament. Extensive incorporation of the gas was then possible at as low film temperatures as — 80°C.Item Adsorption of Xenon and Hydrogen Atoms and their Interaction on Silver Films(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Knapp, A. G.; Stiddard, M. H. B.The adsorption of xenon, hydrogen, and mixtures of xenon and hydrogen on silver films at 77 K has been investigated by measurement of surface potentials by the diode method. Average surface potentials of xenon and hydrogen at maximum coverage were found to be 0.47 V and —0.32 V respectively, in agreement with previous investigations. Hydrogen was adsorbed only when atomized and at a rate which decreased with coverage. When xenon and hydrogen atoms were adsorbed together on silver, considerable interaction between them was indicated. Under certain conditions, addition of xenon to hydrogen adsorbed on a silver surface resulted in desorption of hydrogen. This desorption does not involve simple displace ment of hydrogen as has been observed in other systems. Addition of xenon appears to “ activate ” a certain number of surface hydrogen atoms in such a way that the probability of their reacting with gas phase hydrogen atoms is increased. A quantitative model which accounts for the variation in hydrogen pressure with time during the desorption process has been set up.