On-line mass spectrometric studies on the interaction between organic adlayers on platinum. Part 1. Consecutive adsorption of formic acid and propargyl alcohol

Abstract

The individual interaction of propargyl alcohol (PA) and formic acid (FO) with platinum in acid media leads to a series of adsorbed species that are oxidized at different potentials. The oxidation peak for FO adsorbates is apparent at 0.70–0.80 V. PA residues are oxidized at higher potentials, showing a broad peak centred at 1.25 V. The maximum surface coverage obtained from formic acid is found to be 0.85, whereas for PA adsorbates the platinum surface is completely blocked. The interaction of PA with a platinum surface previously covered by FO species produces adsorbates showing two contributions during electro-oxidation. The first contribution is positively shifted by 0.07 V compared with the original FO peak, whereas the second is apparent in the same potential range as the original PA residues. Differential electrochemical mass spectrometry (DEMS) using isotope-labelled H 13COOH allows the contributions of propargyl alcohol and formic acid during the electro-oxidation of the adsorbates to be distinguished clearly: PA oxidizes to 12CO 2 ( m z = 44 ) whereas FO produces 13CO 2 ( m z = 45 ). It is found that no replacement of formic acid adsorbates occurs during the adsorption of PA. No adsorption of FO is observed when the platinum surface is modified by adsorbed PA.