Interaction between residues of different organic compounds on platinum: a mass spectrometric study

Elena Pastor,Candelaria M Castro,José L Rodríguez,Sergio González

doi:10.1590/s0103-50531997000200004

Abstract

The consecutive adsorption of formic acid and propargyl alcohol, as well as that of formic acid and ethanol on platinum in acid media were studied by on-line mass spectrometry (DEMS). Oxidation of the coadsorbed species remaining on the electrode surface after a flow-cell experiment yields only CO2. Using isotopically labeled H13COOH, the contribution of formic acid during the electro-oxidation of the coadsorbates can be distinguished from that of ethanol or propargyl alcohol residues. It is found that ethanol replaces formic acid residues, whereas the adsorption of propargyl alcohol is modified by the presence of formic acid on the surface. Formic acid cannot chemisorb on a platinum surface covered by propargyl alcohol residues, but reacts without replacement with platinum modified by ethanol residues.

Highlights

The nature of the catalytic poisons formed during the successive adsorption of different organic compounds obviously depends strongly on the structure of the initial compound[1,2,3,4,5,6], and the electro-oxidation of these residues occurs in different potential regions, depending on the composition of the adlayer
A small anodic current transient of 6 μC cm-2 was obtained during the adsorption of propargyl alcohol at Ead = 0.30 V on a platinum surface covered by formic acid residues (Table 1)
The application of Differential electrochemical mass spectrometry (DEMS) using isotopically labeled compounds to study multicomponent systems makes it possible to distinguish the contributions of the different compounds in the coadlayer

Summary

Introduction

The nature of the catalytic poisons formed during the successive adsorption of different organic compounds obviously depends strongly on the structure of the initial compound[1,2,3,4,5,6], and the electro-oxidation of these residues occurs in different potential regions, depending on the composition of the adlayer. The aim of the present work is to elucidate the processes taking place when a second compound reacts on a surface already modified by the presence of a first layer of organic residues. With this purpose, three simple molecules were chosen in order to study the interaction between their residues on platinum: formic acid (HCOOH)[1,2], ethanol (CH3CH2OH)[3], and propargyl alcohol (HC≡CCH2OH)[4,5,6]. COad oxidation occurs in the double layer region. In the case of ethanol, the residues are mainly oxidized in the double layer region.

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