Weakening the C[sbnd]C bond: On the behavior of glyoxylic acid on Pt(111) and its vicinal surfaces

Abstract

Adsorption and oxidation of glyoxylic acid (GA) on platinum single crystals were investigated by spectroelectrochemical techniques. Among basal planes, Pt(111) is taken as a model surface for reactivity studies in order to point out the CC bond breaking. For a standard GA concentration (0.1M), self-poisoning by adsorbed CO (COads) is the main process dominating the positive-going sweep. The presence of (110) steps on (111) terraces contribute in the CC bond cleavage, leading to CO formation, while (100) steps do not show a significant effect. Poison stripping allows GA oxidation in a lower potential range in the negative-going sweep. By working with different GA concentrations (10−5–0.1M), surface blockage is hindered, pointing out an alternative reaction pathway, where GA is oxidized in a poison-free surface. Fourier transform infrared spectroscopy (FTIR) experiments allowed the identification of CO2, formic (FA) and oxalic acid (OA) as main products of GA oxidation. We highlight an activity peak at 0.01M GA, concomitant to the presence of CO2 absorption bands at lower potentials (0.2V). The formation of CO2 at potentials where CO cannot be oxidized suggests a change in the preferential reaction pathway, where GA is completely oxidized through an active intermediate distinct to COads.