The enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Role of TiO2 coated on Al2O3 as a novel support for cinchonidine-modified Pd catalysts

Abstract

The TiO2-coated Al2O3 composites with various TiO2 wt.% loadings were synthesized by the sol–gel method and were used as supports for the Pd-based catalysts to evaluate the enantiomeric excess (ee) of the hydrogenation of (E)-α-phenylcinnamic acid. The physicochemical properties of the composites and the Pd-based catalysts were characterized. The results reveal the strong influence of the TiO2 wt.% loading on the ee value, which is attributed to the effect of pore diffusion. The 5%TiO2/Al2O3 support, which can diminish most of small mesopores in Al2O3 template while remain most of large mesopores, exhibits the highest ee. Our results demonstrate the promising application of mixed oxides as novel supports to improve ee values of the asymmetric hydrogenation of unsaturated prochiral compounds.