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 Al 2 O 3 @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/Al 2 O 3 @SBA-15 catalysts afforded better results when alumina loading in Al 2 O 3 @SBA-15 composites reached above 15 wt.%. Nevertheless, the catalytic performance of Pt/Al 2 O 3 @SBA-15 catalysts was affected by preparation methods for Al 2 O 3 @SBA-15 composites. Ultrasonic impregnation of SBA-15 with an aqueous solution of aluminum nitrate led to uniformly dispersed Al 2 O 3 @SBA-15 composites and then enhanced the interaction between SBA-15 silica and alumina. Correspondingly, the Pt/Al 2 O 3 @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. [ABSTRACT FROM AUTHOR]