Electrochemical oxidation of adsorbed terminal alkenes as a function of chain length at Pt (111) electrodes

On electrocatalysis in alkene–molybdenum(VI) system at Pt/acidic solution interface

“…A plausible reason for such regularity may be a stronger adsorption of 1-butene, and in consequence, higher activation energy of its reductive desorption than that characteristic of propene and ethene. This is consistent with a general trend of increasing adsorption affinity with a growing number of carbon atoms in the molecule of organic compounds, which was well recognised for various metal electrodes [10][11][12]. Additionally, the inductive effect of the electron-repelling alkyl group favours charge donation from the π orbitals of the double C=C bond to the vacant orbitals of Pt in passing from ethene to propene and to 1-butene.…”

Surface electrochemistry

“…Adsorption of unsaturated hydrocarbons from solution or from vapor near atmospheric pressure at Pt(lll) produces adsorbed species different from those obtained by adsorption at room temperature under ultrahigh vacuum.26,47 Species adsorbed from solution resemble the parent compounds much more closely than those adsorbed from vacuum. 23,25,26 The details and underlying causes of these differences are being sought. Immersion of the metal surface into electrolyte solution prior to contact between the surface and the adsorbate tends to moderate the reactivity of the surface toward the adsorbate.…”

“…A primary method for calibration of an Auger spectrometer for quantitative purposes such as measurement of packing density (T, nmol/cm2) is to compare the derivative Auger signal (dz//dE2, A/eV2) with a coulometric measurement for the same surface. The coulometric surface reaction can be an irreversible oxidation in cases where the reaction stoichiometry is known5, 11,15,20,23,25,26 or a reversible redox reaction of a pendant hydroquinone or other redox center.12,13,16 A secondary approach to calibration of Auger spectrometers is to obtain spectra of an adsorbed molecular layer which gives a definitive LEED pattern in which the number of molecules in the unit cell is already known.11,12,16 Normalization of Auger signals from the adsorbed layer by an Auger signal from the clean substrate minimizes the influence of characteristics of an individual spectrometer. Normalized signals due to NA at various packing densities16 are graphed in Figure 5A.…”

“…Most adsorbed alkenes, alkynes, and aromatic compounds at Pt(lll) surfaces undergo oxidation at Pt(lll) electrode surfaces in acidic, aqueous electrolytes at electrode potentials near 0.9 V (vs Ag/AgCl reference). 23,25,26,51 Measurements of the number of electrons, nQi, transferred during oxidation of each adsorbed molecule provide a first indication of the stoichiometry of the oxidation process: I for a series of terminal alkenoic acids (C3-C6, C7, and Cn),23 alkenols (C3-C6 and Cn),25 and alkenes (C2-X6, C8, and C10).26 The alkenoic acids and alkenols were adsorbed from dilute aqueous solutions, while the alkenes were adsorbed from the vapor at atmospheric pressure (C2-C4) or at the vapor pressure. The packing densities of all of the alkenoic acids were similar (near 0.5 nmol/cm2), close to the theoretical limiting packing density of propenoic acid based upon molecular models of the horizontal orientation (0.430 nmol/cm2), Figure 9.…”

Propene Oxidation and Hydrogenation on a Porous Platinum Electrode in Acidic Solution

“…Actually, most of the available information on this subject concerns the adsorption, cathodic hydrogenation, and anodic oxidation of ethene on Pt, showing a particularly high electrocatalytic activity among the transition metals. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In earlier papers, several possible mechanisms of the aforementioned processes were considered on the basis of the kinetic data obtained with the classical electrochemical methods, without any direct identification of reactive intermediates and reaction products. [1][2][3][4][5][6] Some preliminary information on the chemical properties of the ethene adsorbate formed on the Pt-(111) electrode was elucidated ex situ, by means of Auger spectroscopy (AES) in a vacuum.…”