Palladium–copper-exchanged Y type zeolites: a true heterogeneous Wacker catalyst

Abstract

Evidence is presented that faujasite-type zeolites with specific Si : Al framework ratios exchanged with Pd(NH₃)₄²⁺ and Cu²⁺, catalyse the oxidation of ethylene into acetaldehyde, in exactly the same way as the homogeneous Wacker system [Pd^II and Cu^II in concentrated chloride solution]; the active centre is found to be a partially ammoniated Pd^II ion, most probably Pd^II(NH₃)₂, which itself belongs to an electron transfer chain consisting of the alkene reagent, the faujasite encaged Pd_II/Pd⁰ and Cu^II/Cu^I redox couples and dioxygen.