Coadsorption, non-reactive displacement and cathodic desorption of ethene preadsorbed on Pd and Pt electrodes

From both Pd and Pt electrodes, ethene is desorbed at low potentials under hydrogenation as shown by differential electrochemical mass spectrometry (DEMS). The deposition of Cu on the ethene-covered Pt surface leads to the desorption of only 10% of the adsorbate as ethene itself, contrary to the case of benzene, which can be almost completely displaced. The same amount of desorbing ethene is found when adbsorbing I(-) or CO onto the ethene-precovered surface. In the case of Pd, such a partial displacement is only observed when using I-as the displacing agent; CO and CU(2+) lead to coadsorption. (C) 1998 Elsevier Science B.V.