Abstract
(Figure Presented) Tilt it a little: X-ray absorption spectroscopy and photoemission were used to elucidate the mechanism of promoter action in the Cu-catalyzed chemoselective hydrogenation of crotonaldehyde. Sulfur adatoms electronically perturb the C=O bond and tilt the C=C bond away from the surface, thus activating the former and rendering the latter inert to hydrogenation. Quantitative conversion of the reactant with 100% selectivity may be achieved