Due to a general feedstock shift, the chemical industry is charged with the task of finding ways to transform renewable ketones into value-added products. A viable route to do so is the electrochemical hydrogenation of the carbonyl functional group. Here we report a study on acetone reduction at platinum single-crystal electrodes using online electrochemical mass spectroscopy, in situ Fourier transform infrared spectroscopy and density functional theory calculations. Acetone reduction at platinum displays a remarkable structural sensitivity: not only the activity, but also the product distribution depends on the surface crystallographic orientation. At Pt(111) neither adsorption nor hydrogenation occur. A decomposition reaction that deactivates the electrode happens at Pt(100). Acetone reduction proceeds at the (110) steps: Pt[(n – 1)(111) × (110)] electrodes produce 2-propanol and Pt[(n + 1)(100) × (110)] electrodes produce propane. Using density functional theory calculations, we built a selectivity map to explain the intricacies of the acetone reduction on platinum. Finally, we extend our conclusions to the reduction of higher aliphatic ketones.