Pt nanoparticles entrapped in ordered mesoporous carbon for enantioselective hydrogenation

Pt nanoparticles entrapped in CMK-3 ordered mesoporous carbon materials, prepared by a facile impregnation method, were found to be efficient for the enantioselective hydrogenation of α-ketoesters by modification with cinchona alkaloids. The initial activity of higher than 23,000 h^-1 TOF and 82% ee were obtained for the chiral hydrogenation of ethyl pyruvate with cinchonidine (CD)-modified Pt/CMK-3 catalyst. With regard to the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate, the CD-modified Pt/CMK-3 catalyst afforded the highest TOF of 5615 h^-1 and 64% ee. For comparison, commercially available Pt/C and Pt/Al₂O₃ catalysts were investigated as well. The Pt/CMK-3 catalysts were more efficient than the commercial Pt/C catalyst. Of particular note is that the Pt/CMK-3 catalyst exhibited good stability; only below 0.005% Pt atoms were leached into solution after the chiral hydrogenation of ethyl pyruvate in acetic acid, while the Pt leaching amount for the commercial Pt/Al₂O₃ and Pt/C catalysts was 0.15% and 0.25%, respectively. In addition, the Pt/CMK-3 catalyst could also be reused for more than 5 times without distinct loss of activity and enantioselectivity, while the reusability for the commercial Pt/C and Pt/Al₂O₃ catalysts was poor. Based on IR and Raman spectroscopic characterization, it is suggested that both the physical structure features, including high specific surface area, adequate pore volume, ordered mesopores and small Pt particle size with high dispersion, and the chemical nature of catalyst surface with high electron density would improve the performance of Pt/CMK-3 catalysts.