Ralph P. Cooney

Raman spectra of Graphon carbon black

Abstract The Raman spectrum of Graphon carbon black has been recorded using rotating cell techniques. Angular dependence of scattering at 1360, 1580 and 2700 cm−1 are reported and these data suggest that the 1360 cm−1 line is associated with non-planar microstructure distortions. The excitation frequency dependence of the intensity ratio of the bands at 1360 (D) and 1580 cm−1 (G) is interpreted in terms of resonance (vibronic) interaction. This dependence is primarily the result of an increase in the intensity of the 1360 cm −1 line. The disorder-associated line (D) exhibits a significant excitation-dependent shift from 1378 cmi−1 (457.9 nm Ar+) to 1330 cm−1 (647.1 nm Kr+). The “graphite” (G) line position is less sensitive to changes in excitation frequency. The spectral features are discussed in terms of factor group, C6v4, and layer site symmetry, C3v. Also the possible role of localized alkene-like structure in zones of structural distortion is considered.

Carbon dioxide conversion to hydrocarbons at silver electrode surfaces: Raman Spectroscpic evidence for surface carbon intermediates

Abstract Intense Raman spectra from silver electrode surfaces at −0.2 V (SCE) in 0.1 M KF (and other electrolyte) solutions are interpreted in terms of graphitic carbon surface layers. Similar spectra have been recorded from dry silver surfaces polished in an atmosphere of air or CO 2 . The source of carbon in the electrochemical studies appears to be atmospheric CO 2 which generates the electroactive species: aquated CO 2 (at pH 5.5) and CO 3 2− (at pH 11). It appears probable that CO 2 in its solution form is electroreduced to an unstable silver surface-formate complex which in turn spontaneously decomposes to carbon.

A Fourier-transform infrared spectral study of H-ZSM-5 surface sites and reactivity sequences in methanol conversion

Surface sites on a series of dealuminated zeolitic catalysts of the H-ZSM-5 and mordenite types have been investigated using Fourier-transform-infrared spectroscopy (FT-ir). Three types of H-ZSM-5 surface site have been considered in detail: dealumination-associated Bronsted-silanol sites, aluminum-associated Bronsted-silanol sites, and Lewis sites. Sequences of populations of these sites have been identified using three methods: silanol stretching mode absorbance changes, relative changes in absorbance of adsorbed pyridine modes, and analytical data from X-ray fluorescence (XRF) characterizing the extracted surface layer. In the case of the method based on adsorbed pyridine a novel treatment has been developed which permits Bronsted (B)/Lewis(L) site ratios to be calculated as a function of temperature. This method reveals that the [B][L] ratio exhibits a maximum at ca. 473 K which is associated with the dealumination Bronsted sites. Comparison of sequences of site populations with observed reactivities suggests that Lewis sites are the origin of catalytic activity in the conversion of CH3OH to (CH3)2O. Similar comparisons indicate that dealumination Bronsted sites are the principal source of reactivity for the conversion of (CH3)2O to hydrocarbons. The migration of aluminum atoms away from the surfaces of ZSM-5 during calcination is invoked to explain the resistance of precalcined catalysts to acid dealumination.

Intense raman spectra of surface carbon and hydrocarbons on silver electrodes

Abstract Raman spectra have been recorded from silver electrodes in salt solutions at −0.2 V (SCE). Enhancement of the spectra is interpreted in terms of red-light transmittance of high surface area carbons on the electrodes. The kinetics of diffusion of the hydrocarbons away from the electrode is shown to be much slower than the rate of formation of hydrocarbons.

Chemical reactivity and surface-enhanced raman scattering

Abstract A mechanism is proposed for surface-enhanced Raman scattering for pyridine which explains the enhancement, the anodizalion “activation”, the significance of silver, the photographitization of coordinated pyridine and formate, the participation of surface roughness, and the irreversibly held yet liquid-like nature of surface pyridine.

Surface-enhanced raman spectra of benzene at silver electrodes

Abstract Raman spectra of benzene adsorbed on silver electrodes exhibit a ring-breathing mode at ≈992 cm-1, which coincides with the line position of the same mode in liquid benzene. This result argues against chemisorption on a metal surface and in favour of physisorption on a surface carbon phase.

The adsorption of cyclopropane on zeolite HY

Abstract Infrared and mass spectral evidence indicates that when cyclopropane is passed over zeolite HY at room temperature isobutane is formed as a major product. A mechanism for this transformation involving the formation of a nonclassical protonated cyclopropane ion intermediate is proposed. At 200 °C and above cyclopropane isomerizes to propylene and also forms aromatic species.

Resonance Raman spectra of polyacetylene on zeolite and alumina surfaces

Abstract Raman spectra are reported for polyacetylene on exchanged zeolites and on alumina. The polymerization of acetylene on zeolites is found to depend on the zeolitic cation size and on surface coverage. Mean chain lengths of about fifteen CC bonds are formed on alumina.

Raman evidence for the photochemical formation of cyanide from acetonitrile on copper electrodes

Abstract Laser Raman spectra from the system: Cu/CH 3 CN, NaClO 4 , H 2 O, reveal evidence for cyanocopper(I) species in the interfacial region. The cyanide appears to originate in the laser-assisted decomposition of coordinated acetonitrile in O 2 -rich aqueous electrolyte. The evidence for the involvement of laser photochemistry comes from uniform laser-flux perturbations of the cyclic voltammetry for the system. Parallel studies for the corresponding silver electrode system reveal evidence for the exhaustive, and probably laser-assisted, electro-oxidation of acetonitrile into nitrates and carbonates.

Raman spectra of benzene adsorbed at the aqueous/silica and vapor/silica interfaces

Abstract Raman spectra are reported for benzene adsorbed at the aqueous/silica and vapor/silica interfaces. A spectroscopic cell suitable with modification for either solution adsorption or vapor adsorption studies is described. The cell permits in situ surface precleaning and in the case of solution adsorption studies it ensures the exclusion of external contaminants. A comparison of spectral data for adsorption from aqueous solution and from the gas phase reveals differences which can be related to the role of solvent water (D 2 O) in the former case. Aspects of the data from vapor/silica interfaces (viz., CH stretching mode displacement and changes in relative intensities) are interpreted in terms of first-layer and higher-layer effects.