Pt nanoparticles entrapped in Al2O3@SBA-15 composites: Effective and recyclable catalysts for enantioselective hydrogenation of ethyl 2-oxo-4-phenylbutyrate

• Al2O3@SBA-15 composites prepared by different methods to support Pt nanoparticles.
• Pt/Al2O3@SBA-15 catalyst is effective for chiral hydrogenation of α-ketoesters.
• Catalysts are more efficient than Pt/Al2O3 catalyst under the similar conditions.
• Catalysts can be reused for at least seven times in acetic acid.
• Up to 11,928 h−1 TOF was achieved with Pt/Al2O3@SBA-15 catalyst.

Solid-state grinding, ultrasonic impregnation and conventional impregnation methods were adopted to synthesize mesoporous composites Al2O3@SBA-15 supported Pt catalysts for chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate after modified with cinchonidine. Compared with Pt/SBA-15 or Pt/alumina catalyst, Pt/Al2O3@SBA-15 catalysts afforded better results when alumina loading in Al2O3@SBA-15 composites reached above 15 wt.%. Nevertheless, the catalytic performance of Pt/Al2O3@SBA-15 catalysts was affected by preparation methods for Al2O3@SBA-15 composites. Ultrasonic impregnation of SBA-15 with an aqueous solution of aluminum nitrate led to uniformly dispersed Al2O3@SBA-15 composites and then enhanced the interaction between SBA-15 silica and alumina. Correspondingly, the Pt/Al2O3@SBA-15 catalyst prepared by this method showed the best results (up to 11,928 h−1 TOF and 87.9% ee) and could be reused for several times. Based on the spectroscopic characterizations, we deduced that the acidity of the composites, the Pt particle size and dispersion, and the electronic properties of Pt particles played vital roles in determining the catalytic performance.

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