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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 Infrared Study of Carbon Monoxide Adsorption on Calcium and Strontium Oxides(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Coluccia, Salvatore; Garrone, Edoardo; Guglielminotti, EugenioCO adsorption on CaO and SrO takes place, as on MgO, via a disproportionation reaction leading to both surface carbonates and unusual surface species with a complex vibrational spectrum in the low-frequency range. These are thought to be negatively charged CO polymers, the simplest ones being (CO)2–2. A strong electrostatic interaction between negative species and surface cations accounts for the marked dependence of the infrared signal on the lattice parameter of the solids. The increasing basicity along the series MgO, CaO, SrO causes: (i) a marked increase in the total adsorptive capacity; (ii) an increase in the relative population of polymers with respect to dimers; (iii) an increase in the importance of a Boudouart-like reaction upon desorption.Item Infrared Study of the Adsorption of Aromatic Esters on Silica Immersed in Carbon Tetrachloride(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Cross, Stephen N. W; Rochester, Colin HInfrared spectra are reported of silica preheated at 843–948 K and immersed in solutions of benzyl acetate, ethyl benzoate and benzyl benzoate in carbon tetrachloride. The predominant surface–adsorbate interaction involved the formation of hydrogen bonds between isolated surface silanol groups and the (C[double bond, length as m-dash]O)-groups of adsorbed ester molecules. A small proportion of the adsorbed ester molecules were each linked to the silica surface via two hydrogen bonds, one involving the (C[double bond, length as m-dash]O)-group and the other involving aromatic π-electrons. The results are compared with previous data for the adsorption of ethyl acetate and ethyl cyanoacetate and are discussed in relation to the electronic effects of substituent groups in the ester molecules.Item Infrared Study of the Adsorption of Ethyl Cyanoacetate on Silica Immersed in Carbon Tetrachloride(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Cross, Stephen N. W; Rochester, Colin HInfrared spectra are reported of silica immersed in solutions of ethyl cyanoacetate in carbon tetrachloride. The surface–adsorbate interaction for silica which had been preheated at 1073 K involved the formation of hydrogen bonds between pairs of isolated surface silanol groups and both the cyano and carbonyl groups in each adsorbed ethyl cyanoacetate molecule. For silica which had been evacuated at 298 K adjacent interacting surface silanol groups also provided sites for the adsorption of ethyl cyanoacetate. The adsorbed molecules were again bonded to the surface via both their cyano and carbonyl groups. Each carbonyl group was involved in a hydrogen bonding interaction with a single surface silanol group. This contrasts with the observation that pairs of adjacent interacting silanol groups each formed two hydrogen bonds with the carbonyl oxygen atom of a single ethyl acetate molecule adsorbed on silica immersed in carbon tetrachloride.Item Solvation Spectra Part 54.1—A Low Temperature Infrared Spectroscopic Study of the Solvation of Ions in Methanol(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (11), 1977) Strauss, Imants M; Symons, Martyn C. RBroad featureless bands in the O—H stretching region for CH3OH in CH3OD containing a range of 1:1 electrolytes become narrower on cooling below the glass point and usually display several features. Lithium and sodium salts up to ∼3 mol kg–1 show narrow bands on the high-frequency side of the bulk methanol band that are assigned to solvent molecules bonded to the anions. The bulk methanol bands are broadened and shifted by the cations, but separate bands for the cation solvates are not resolved. At higher concentrations of salt, the anion bands are also shifted by the cations to give new high frequency bands assigned to solvent shared ion-pairs. Tetra-alkyl-ammonium salts in the 1 mol kg–1 region give new bands characteristic of the anions only. Sodium tetraphenylboron gives a narrow component at 3520 cm–1 and a very broad component centred at ∼3360 cm–1. The former is assigned to two O—H groups bonded to a single methanolic oxygen atom: the latter is assigned to oscillators in short chains or cyclic structures. A broad band at ∼3360 cm–1 for other concentrated electrolyte solutions is assigned similarly.Item Infrared Study of the Adsorption of [2H4]Acetic Acid on to Rutile(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Griffiths, David M; Rochester, Colin HInfrared spectroscopic studies are reported of the adsorption of [2H4]acetic acid onto three samples of rutile which differed in their extents either of hydration or of reduction. Acetic acid was associatively adsorbed on Lewis acidic electron acceptor Ti4+ sites in the rutile surface: this mode of adsorption was prevented by the preadsorption of water or by reduction of rutile in hydrogen. Weakly adsorbed acetic acid dimers appeared on the surface of rutile which had been pretreated in oxygen but not on reduced rutile. Chemisorption of acetic acid generated water, surface deuteroxyl groups and [2H3]acetate ions predominantly in a highly symmetrical bidentate chelate configuration. Both the presence of adsorbed water and prereduction of rutile in hydrogen hindered the chemisorption of acetic acid on rutile.Item Infrared Study of the Adsorption of Hexafluoroacetone on to Rutile(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Griffiths, David M; Rochester, Colin HInfrared spectra have been recorded of hexafluoroacetone adsorbed on four samples of rutile which differed in their extents of dehydration by thermal activation or of reduction in hydrogen. Physically adsorbed hexafluoroacetone molecules interacted as hydrogen bond acceptors with surface hydroxyl groups, as electron donors with Ti4+ ions, and as electron acceptors with Ti3+ ions. Chemisorptive interactions involving surface hydroxyl groups or O2– ions led to the formation of trifluoroacetate ions and precursor species resembling salts of hexafluoropropan-2,2-diol. In general, reduction of rutile in hydrogen weakened adsorptive interactions involving H-bond donation or electron acceptance by the oxide surface. In contrast interactions involving electron donation or nucleophilic attack of hexafluoroacetone by hydroxyl groups or O2– ions were enhanced by reduction of the oxide in hydrogen.Item I.r. Spectroscopic Study of CO2 Adsorption onto q-Al2O3(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Morterra, Claudio; Zecchina, Adriano; Coluccia, Salvatore; Chiorino, AnnaThe adsorption of CO2 at room temperature onto η–Al2O3 dehydrated at various temperatures between 25 and 800°C was studied by i.r. and microgravimetric techniques. The following surface species are formed; three σ-coordinated linear structures, two bicarbonates that can be interconverted, several “organic” carbonates and minor amounts of mono- and bi-dentate carbonates. Relative concentrations of these species depend strictly on pretreatment conditions, while the nature of the species is primarily determined by the coordination of surface cations. The overall coverage is quite small, (θ⩽ 10 %) and nearly the same as in all transition aluminas. A cooperative mechanism for CO2 adsorption is thus invoked to account for this and other features. The interaction between CO2 adsorption and catalytic activity is considered, and the probable nature of the centres responsible for exchange and equilibration reactions is suggested.Item Infrared Study of the Adsorption of Water on to the Surface of Rutile(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (10), 1977) Griffiths, David M; Rochester, Colin H.Infrared spectra of the surface of three samples of rutile which had been (a) calcined in air at 723 K and heated in oxygen at 673 K, (b) calcined in air at 973 K and heated in oxygen at 673 K, and (c) calcined in air at 723 K and heated in hydrogen at 673 K have been recorded as a function of the extent of hydroxylation and hydration of the oxide surface. The adsorption and desorption characteristics of associatively adsorbed and chemisorbed water on rutile have been established in detail and are discussed primarily in terms of adsorptive interactions involving the {110}, {100} and {101} surface planes. Calcination of rutile at high temperature (973 K) enhanced the chemisorption of water on {110} planes at the expense of the associative adsorption of water on Ti4+ ion sites in the {100} and {101} planes. Mild reduction of rutile in hydrogen decreased the ability of the oxide to adsorb water molecularly. The effect of reduction was completely reversed by subsequent heat treatment of the oxide in oxygen.Item Infrared Spectra of NO, N2O, NO2 and Oi Adsorbed on SiO Films(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Lubezky, Aviva; Folman, MordechaiInfrared spectra of nitrogen and oxygen adsorbed on high surface area SiO films were investigated at different temperatures and surface coverages. On adsorption of NO at 77 K and at low coverage, decomposition of the molecule takes place with simultaneous oxidation of the surface. At higher coverages N2O is formed. On partially or completely oxidized surface absorptions due to NO dimers are obtained. On adsorption of NO2 at 136, 250, 273 and 300 K on freshly prepared SiO films decomposition of the molecule takes place with formation of NO and here again complexes with the surface are formed which are similar to those obtained when NO is adsorbed.