This
paper studies the electrochemical hydrogenation of the carbonyl
functional group of acetophenone and 4-acetylpyridine at platinum
single-crystal electrodes. Comparison with results obtained for the
hydrogenation of acetone featuring an isolated carbonyl functional
group reveals the influence of the phenyl ring and the pyridine ring,
respectively. Lack of acetone adsorption at Pt(111) and Pt(100) due
to a weak interaction between surface and carbonyl functional group
renders these surfaces inactive for the hydrogenation of acetone.
Adsorption through a strong interaction with the phenyl ring of acetophenone
activates the Pt(111) and Pt(100) surfaces for hydrogenation of the
acetyl substituent. In agreement with previous results for acetone
reduction, the Pt(100) surface is specifically active for the hydrogenolysis
reaction, breaking the C–O bond, whereas the other surfaces
only hydrogenate the carbonyl functionality. In contrast to the phenyl
ring, the pyridine ring has a very different effect: due to the dominant
interaction of the N atom of the pyridine ring with the platinum electrode,
a vertical adsorption mode is realized. The resulting large physical
distance between the carbonyl functional group and the electrode surface
inhibits the hydrogenation at all platinum surfaces. This also holds
for the Pt(110) electrode, which is otherwise active for the electrochemical
hydrogenation of the isolated carbonyl functional group of aliphatic
ketones. Our results show how the combination of molecular structure
of the reactant and surface structure of the catalyst determine the
selective electroreduction of functionalized ketones.