(513eh) Insights into Koac-Promoted PdAu/SiO2-Catalyzed Vinyl Acetate Synthesis Using in Situ xrd and Drifts

Vinyl acetate monomer (VAM) is one of the most important commodity chemicals produced worldwide, and is synthesized via a gas-phase acetoxylation reaction with acetic acid (AcOH) and ethylene. Serving as a key intermediate for end-use products such as polyvinyl acetate (PVA), polyvinyl alcohol (PVOH), ethylene-vinyl acetate copolymer (EVA), and ethylene-vinyl alcohol copolymer (EVOH), it has numerous applications in the paints and adhesives industries. Since the 1960s and 1970s, PdAu catalysts supported on silica have been shown to be most reactive towards vinyl acetate synthesis. Oftentimes, promoters, namely potassium acetate (KOAc), are added to the catalyst to enhance activity and prevent catalyst deactivation. However, the mechanisms behind this promotion remain unclear. One theory suggests KOAc interacts with homogenous Pd leached from the catalyst present in a condensed liquid film of AcOH and water on the silica support surface, which allows preferential reaction with ethylene. Others maintain that KOAc stabilizes Pd within the PdAu domains.

In this study, PdAu catalysts supported on SiO₂ were synthesized from metal salt precursors using wet impregnation methods. The catalyst was then loaded with KOAc by wet impregnation. Utilizing in situ techniques such as x-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we monitored changes in catalyst structure and surface species as a function of gas atmosphere (ethylene, nitrogen, oxygen, acetic acid and combinations thereof) to gain insights into the role of KOAc promoter. By coupling in situ XRD with in situ DRIFTS analysis, we can gain insights into the mechanisms of how KOAc affects catalyst performance.