Electrocatalytic hydrogenation and oxidation of aromatic compounds studied by DEMS: Benzene and p-dihydroxybenzene at ultrathin Pd films electrodeposited on Au( hkl) surfaces

• Published in: Journal of colloid and interface science Vol. 314; no. 1; pp. 152 - 159
• Main Authors: Sanabria-Chinchilla, J., Baricuatro, J.H., Soriaga, M.P., Hernandez, F., Baltruschat, H.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.10.2007; Elsevier
• Subjects: Anodic oxidation of aromatic compounds; Chemistry; Colloidal state and disperse state; Differential electrochemical mass spectrometry; Electrocatalytic hydrogenation of aromatic compounds; Electrochemistry; Exact sciences and technology; General and physical chemistry; Kinetics and mechanism of reactions; Pd-modified Au( hkl) surfaces; Surface physical chemistry; Ultrathin palladium films; Pd-modified Au( hkl) surfaces; Ultrathin palladium films; Differential electrochemical mass spectrometry; Electrocatalytic hydrogenation of aromatic compounds; Anodic oxidation of aromatic compounds; Film; Transition metal; Palladium; Hydrogenation; Pd-modified Au(hkl) surfaces; Electrocatalysis; Benzene; Electrochemistry; Aromatic compound; Oxidation; Platinoid; Mass spectrometry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2007.05.024

Differential electrochemical mass spectrometry (DEMS) was used to investigate the electrocatalytic hydrogenation and oxidation of benzene and p-dihydroxybenzene (hydroquinone, H 2Q) chemisorbed on ultrathin Pd films electrodeposited at Au(332) and Au(111) surfaces. At low sub-monolayer coverages on Au(332), the Pd ad-atoms preferentially adsorb on the step sites. At higher (but still sub-monolayer) coverages, Pd also occupies terrace sites; on Au(111), only terrace sites are available. The electrochemical reactivities of the subject compounds at the Pd-decorated steps and terraces were then compared. No hydrogenation products were detected by DEMS for either benzene or H 2Q, but a considerable degree of electrodesorption of (intact) benzene occurred near the hydrogen-evolution region (HER). Anodic oxidation of both compounds yielded only CO 2 as the volatile (DEMS-detectable) product, although it took up to three anodic cycles to attain exhaustive (complete) oxidation. The anodic oxidation of benzene was also accompanied by potential-induced desorption of (unreacted) benzene particularly in the case of the stepped surface. Electrodesorption at the HER was more facile at the terrace sites than from the step sites; the opposite was true for electrodesorption at the more positive potential. Contrary to hydrogen, which does not adsorb at such monoatomic rows, both aromatic species adsorb when the nominal Pd coverage just corresponds to step decoration. Anodic oxidation of chemisorbed hydroquinone yielded CO 2 as the only DEMS-detectable product. No hydrogenation products for benzoquinone could be identified by DEMS. For benzene, a considerable fraction of starting material was electrodesorbed near the hydrogen-evolution region.