|dc.description.abstract||The chemisorption and electrochemical hydrogenation of hydroquinone (H2Q) at
polycrystalline (pc) Pd, well-ordered Pd(100), and Pd-modified Au(hkl) electrodes were
studied using a combination of ultra-high vacuum (UHV) surface spectroscopy,
electrochemistry (EC), and electrochemical mass spectrometry (EC-MS). H2Q was
found to form a slightly tilted flat-oriented quinone (Q) adlayer, when adsorbed from
low concentrations; when chemisorbed from high concentrations, an edgewise-oriented
H2Q adlayer was indicated.
The hydrogenation of the chemisorbed layer is initiated at potentials before the
onset of the hydrogen evolution region. As expected, the kinetics increases as the applied
potential is increased, but the hydrogenation pathway appears to be independent of the
potential. Hydrogenation in the absence of absorbed hydrogen (sub-surface) was studied
at ultra-thin Pd films on Au single-crystal substrates. Hydrogenation and/or potential
induced desorption were established, although non-volatile and/or hydrophobic products
were detected. In comparison, negative excursions with benzene-coated electrodes
resulted in nothing more than potential-induced desorption of the starting material.
Negative-potential electro-desorption was more facile at terraces than at steps.
Vibrational spectroscopic measurements suggested that hydrogenation occurs one
molecule at a time to the fullest extent that resulted in desorption of product; that is,
partially hydrogenated species do not exist on the surface.||