Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt_3Sn and unsupported PtRu_(0.2) catalysts: A quantitative DEMS study

摘要

The oxidation of acetaldehyde on carbon supported Pt/Vulcan, PtRu/Vulcan and Pt_3Sn/Vulcan nanoparticle catalysts and, for comparison, on polycrystalline Pt and on an unsupported PtRu_(0.2) catalyst, was investigated under continuous reaction and continuous electrolyte flow conditions, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements. Product distribution and the effects of reaction potential and reactant concentration were investigated by potentiodynamic and potentiostatic measurements. Reaction transients, following both the Faradaic current as well as the CO_2 related mass spectrometric intensity, revealed a very small current efficiency for CO_2 formation of a few percent for 0.1 M acetaldehyde bulk oxidation under steady-state conditions on all three catalysts, the dominant oxidation product being acetic acid. Pt alloy catalysts showed a higher activity than Pt/Vulcan at lower potential (0.51 V), but do not lead to a better selectivity for complete oxidation to CO_2. C-C bond breaking is rate limiting for complete oxidation at potentials with significant oxidation rates for all three catalysts. The data agree with a parallel pathway reaction mechanism, with formation and subsequent oxidation of CO_(ad) and CH_(x, ad) species in the one pathway and partial oxidation to acetic acid in the other pathway, with the latter pathway being, by far, dominant under present reaction conditions.