Examination of catalytic behavior and origin of the initial transient period for Pt nanoclusters modified with cinchonidine

Abstract

Nanoclusters prepared by a novel water-free method are compared directly with nanoclusters prepared by the known aqueous preparation as well as conventional Pt/Al2O3 for the enantioselective hydrogenation of ethyl pyruvate. The catalytic behavior of cinchonidine on colloidal Pt was investigated during ethyl pyruvate hydrogenation in acetic acid under 10 bar of hydrogen at 22 °C with (1 mmol L−1) and without addition of free cinchonidine. The effect of hydrogen pressure, cinchonidine concentration, ethyl pyruvate and catalyst loading on the enantiomeric excess (EE) with time were also studied. Through these studies, we propose that the nature of the observed initial transient period (ITP) for these “quasi-homogeneous” systems may be explained by desorption of the weakly adsorbed tilted “N lone pair bonded” cinchonidine species from the Pt surface due to interaction with hydrogen.