MECHANISM OF THE WACKER OXIDATION OF ALKENES OVER CU-PD-EXCHANGED Y-ZEOLITES

The catalytic potential of CuPd zeolites with faujasite topology in the Wacker oxidation of 1-alkenes with dioxygen is reported and compared with that of a homogeneous PdCl2-CuCl2 salt solution. The influence of water, oxygen, and alkene partial pressure on the rate of oxidation and the use of different alkenes and perdeuterated ethene as substrate allowed to establish similarities between the heterogeneous and homogenous system as well as specific zeolite effects. In situ IR and ESR spectroscopy of a working catalyst allowed to propose an active site consisting of a trinuclear Cu-O-Pd-O-Cu cationic complex and a catalytic cycle for the Wacker oxidation in which the reoxidation of Cu+ by dioxygen or of Pd-0 by zeolite Cu2+ is rate determining. Diagnostic probing of the phenomena with CO in IR and ESR confirmed this picture.