On the Promotional and Inhibitory Effects of Water on Wacker-Type Ethylene Oxidation Over Pd–Cu/Zeolite Y

Kinetic studies reveal the rate-enhancing and rate-inhibiting effects of water on Wacker-type ethylene oxidation at low and high partial pressures, respectively. Through time-resolved X-ray absorption spectroscopy (XAS), a highly dynamic speciation of palladium and copper in the catalyst under steady state and transient conditions involving water-switching experiments is identified. Water is demonstrated to play key roles in the reoxidation of Pd(0) and Cu(I), aided by increased ion mobility, which we posit facilitate a more efficient electron transfer in the heterogeneous Wacker process.