Some insights into the preparation of Pt/γ-Al₂O₃ catalysts for the enantioselective hydrogenation of α-ketoesters

Pt/γ-Al₂O₃ catalysts were prepared by two different impregnation methods and characterized by XRD, TEM, and CO chemisorption. The Pt particle sizes ranged in 2.4-23.3 nm for these Pt-γ-Al₂O₃ catalysts. CO was used as a probe molecule. Due to the interaction of platinum precursor with γ-Al₂O₃, induced particularly after the calcination at high temperature, the Pt/γ-Al₂O₃ catalysts prepared by impregnation, calcination, and reduction in a sodium formate solution exhibited higher activities for both the enantioselective hydrogenations of ethyl pyruvate and ethyl 2-oxo-4-phenylbutyrate. The Pt/γ-Al₂O₃ catalysts, prepared by impregnation in a solution containing isopropanol without drying or calcination, did not show high catalytic performance in the enantioselective hydrogenation of ethyl pyruvate because the surface properties after the addition of isopropanol are not beneficial to the adsorption of reactant, solvent, and chiral modifier, or because the residual isopropanol blocked the adsorption of reactant, solvent, and chiral modifier.