One promising way to develop efficient noble-metal catalysts is to induce the exposure of specific catalytically active facets of nanocrystals through shape-controlled syntheses. However, as for the as-prepared noble-metal nanocrystals, there are commonly residual capping agents adsorbed on the metal surfaces, which have complex effects on the catalytic activity and selectivity in different catalytic reactions. In this paper, by taking polyvinylpyrrolidone (PVP), the most commonly used capping agents in the shape controlled synthesis of noble-metal nanocrystals, as an example, we systematically studied the surface-modification effects of residual capping agents in the enantioselective hydrogenation of acetophenone. It was found for the first time that the residual PVP adsorbed on the Pd concave tetrahedron nanocrystals is detrimental to the enantioselectivity, negative to the activity, while positive to increase the chemoselectivity to the carbonyl group. The loss of enantioselectivity over PVP-stabilized Pd concave tetrahedron nanocrystals is probably due to that the residual PVP adsorbed on the Pd surface can interact with the chiral modifier S-proline and prevent the requisite interaction between S-proline and acetophenone co-adsorbed on the Pd surfaces. Thus, the prochiral interaction complexes which play a significant role in determining the enantioselectivity cannot be formed. KBH4 treatment or hot water reflux offers feasible methods to further reduce the amount of residual PVP adsorbed on the Pd nanocrystals and to achieve enantioselectivity in the enantioselective hydrogenation of acetophenone. This study provides useful information to reveal the essence of enantiodifferentiation in heterogeneous enantioselective hydrogenations, which is beneficial for the design of efficient synthetic protocols and the shape controlled synthesis of noble-metal nanocrystals to obtain pure enantiomers. (C) 2018 Elsevier Inc. All rights reserved.