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

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.