Comparative study of carbonaceous materials as catalyst supports for the enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Influence of the support acidity

Abstract

A systematic comparative study of carbonaceous materials as catalyst supports for the asymmetric heterogeneous hydrogenation of (E)- A- phenylcinnamic acid (PCA) was performed to investigate the influence of the supports on the reaction enantioselectivity. A series of Pd-based catalysts supported on activated carbon, graphene oxide (GO), or carbon nanotubes was prepared using deposition methods, and their physicochemical properties were characterized. The results demonstrated that the textural structure of the supports had a trivial effect on the enantiomeric excess (ee). The TGA, FT-IR, and TPD-NH3 data revealed an abundance of acidic sites present on the Pd/GO catalyst, unlike the other catalysts, and these sites reduced the enantioselective hydrogenation of PCA. The effect of the support acidity on the enantioselectivity was ascribed to the preferential adsorption mode of cinchonidine (CD) on the GO surface via electrostatic interactions between the negatively charged oxygen functional groups present on the GO surface and the positively protonated amine groups present in the CD molecule.