Ethylene, acetic acid and oxygen are the educts to yield vinyl acetate via gas phase acetoxylation. The typical industrially used catalysts are based on silica-supported bimetallic Pd/Au particles promoted with potassium acetate. Under reaction conditions (413-453 K and 5-10 bar) a condensed acetic acid film leads to restructuring of the PdAu particles towards a more reactive and selective surface of 1:1 composition and separated dispersed Pd particles.In this presentation, we will show that the addition of alkaline acetates to PdAu/SiO2 is essential to increase the overall selectivity, activity and stability against deactivation. The presence of KOAc is required to control the equilibrium between Pd in the Pd1Au1 particle and dispersed Pd. Absence of KOAc during the reaction leads to Au-rich particles. Furthermore, Pd can be incorporated into monometallic Au particles in the presence of KOAc by forming a reaction intermediate K2Pd2(OAc)6. The alkaline metal is incorporated in the SiO2 support and in the surface of the PdAu particles indicated by in situ XRD and EXAFS at the Pd K and Au LIIIedge. Figure 1. Scheme for restructuring processes of PdAu particles  . Financial support and fruitful discussions with Wacker Chemie AG are gratefully acknowledged.

Interaction of the alkaline acetate promoter with bimetallic PdAu catalysts for the gas phase vinyl acetate synthesis

248th National Meeting (2014)

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