Synthesis of Vinyl Acetate Monomer Over PdCu Alloys: The Role of Surface Oxygenation in the Reaction Path

Abstract

This work uses sol–gel and sonochemical methods to prepare bimetallic PdCu catalysts supported on modified ZrO₂ with Ti and Al. The catalysts are tested for vinyl acetate synthesis from ethylene, acetic acid, and oxygen, varying the reaction temperature for two catalysts prepared, which show higher activity. Catalysts characterization results show bimetallic species and distort alloys with a dispersed distribution of active metal onto the support. The in situ reaction by DRIFT-MS identifies the surface formation of main intermediates like palladium acetate monomers and mono and bidentate intermediates, associated to vinyl acetate formation, like vinyl hydrogenated species over PdCu. Finally, this behavior will be attributed to the bimetallic distortions of PdCu samples, provided by interaction effects between PdCu and supports, indicating a more exposition of PdCu species suitable for the reaction, according to high-resolution transmission microscopy electron microscopy results for PdCu/ZrTi sample. Thus, this sample exhibits a minimal formation of sub-products and catalytic stability for 18 hh. These results evidence the participation of hydroxyls and oxygen vacancies of the catalyst in the catalytic reaction measured in situ, monitoring the products formed at the reactor outlet. Finally, it is proposed a reaction pathway as a function of reaction conditions.