Heterogeneous enantioselective catalysis is considered a promising strategy for the large-scale production of enantiopure chemicals. In this work, polymer-capped Pt nanocatalysts having a uniform size were synthesized using poly­(vinyl pyrrolidone) (PVP) and poly­(vinyl alcohol) and supported on γ-Al2O3. After a facile heat treatment process, their catalytic performance for enantioselective hydrogenation of α-keto esters, a structure-sensitive reaction, was investigated. The presence of residual capping agents on the Pt surface often perturbs the adsorption of reacting species and reduces performance in structure-sensitive reactions. However, the 1 wt % PVP-Pt/Al2O3 catalyst exhibited an enhancement in both activity and enantioselectivity compared to a reference Pt/Al2O3 catalyst prepared by wet impregnation. Under optimized reaction conditions, the cinchonidine-modified PVP-Pt/Al2O3 gave an enantiomeric excess of 95% for the enantioselective hydrogenation of methyl pyruvate despite the low Pt loading. We demonstrate that depending on the type of polymers, the residual capping agents can lead to site-selective blockage of the Pt surface, that is, defects or terraces. Quantitative and qualitative analyses also show that the noticeable improvement in enantioselectivity is attributed to the stable adsorption of chiral modifiers on selectively exposed Pt terrace sites. The findings of this work provide a promising strategy to prepare metal nanoparticles having selectively exposed sites and offer insights into the enhancing effect of residual capping agents on the catalytic properties in structure-sensitive reactions.

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The development of chiral catalysts is key to the production of enantiopure compounds, which are of great interest to the pharmaceutical and fine chemical industries. The features of heterogeneous catalysts, such as their high stability, easy separation, and facile reusability, are particularly beneficial for practical applications. Supported and chirally modified Pt catalysts have shown high potential in enantioselective hydrogenation of α-keto esters. In this study, we report a highly efficient and versatile Pt/B-SiO2 catalyst. Specially, commercially available SiO2 support was modified with varying amounts of boron via a facile impregnation method. For the enantioselective hydrogenation of methyl pyruvate, 1 wt % Pt/B-SiO2 with a molar ratio of B/Pt = 60 achieved 96% enantiomeric excess (ee) even at H2 pressure of 0.1 MPa and maintained high enantioselectivity during 10 consecutive cycles. For various α-keto esters, the Pt/B-SiO2 catalyst also showed significantly higher activity and enantioselectivity than unmodified Pt/SiO2. Moreover, 0.5 wt % Pt/B-SiO2 outperformed 5 wt % Pt/γ-Al2O3, one of the most efficient catalysts reported for this reaction, despite its 10-times lower Pt loading. The enhanced adsorption capability of B-SiO2 for a chiral modifier and the resulting chiral modification of the Pt surface were found to be responsible for the superior performance of Pt/B-SiO2. This strategy based on the facile surface modification of a commercially available support material provides an opportunity to develop practical and efficient heterogeneous enantioselective catalysts.