DEMS study on the nature of acetaldehyde adsorbates at Pt and Pd by isotopic labelling

Abstract

The formation of acetaldehyde adsorbates on Pt and Pd has been studied applying cyclic voltammetry and differential electrochemical mass spectrometry (DEMS). The adspecies were isolated on the metal surface at selected adsorption potentials (E ad) applying a flow cell procedure under potential control, and the anodic stripping were performed for each E ad. For Pt, two different contributions were established during oxidation: one at E < 0.80 V and the second in the range 0.80–1.50 V in the Pt oxide region. For Pd, the voltammetric profile resembles that for the oxidation of adsorbed CO. DEMS experiments have shown that CO2 was the sole electro-oxidation product in both cases. The oxidation of each C atom in acetaldehyde adsorbates has been distinguished using the isotopic-labelled aldehyde $$ {\left( {^{{12}} CH^{{13}}_{3} CHO} \right)} $$ in DEMS experiments at selected E ad. It was observed that, on Pt, acetaldehyde molecules loose part of the CH3 groups during adsorption at E ad < 0.40 V, whereas the CHO groups are easily oxidized at E ad > 0.40 V. Therefore, both C1 and C2 species are present on the surface, and their yields depend on E ad. On the contrary, on Pd, most of the CH3 groups are lost during adsorption at all E ad, and the main adsorbed species seems to be COad.