Homogeneous-heterogeneous bifunctionality in Pd-catalyzed vinyl acetate synthesis

Area of Science:

• Chemical catalysis
• Materials science
• Electrochemistry

Background:

• Catalysis mechanisms traditionally assume a single active phase (homogeneous or heterogeneous).
• Palladium-catalyzed vinyl acetate synthesis is a significant industrial process.

Purpose of the Study:

• To investigate the mechanistic paradigm of palladium-catalyzed vinyl acetate synthesis.
• To elucidate the role of phase interconversion between heterogeneous and homogeneous palladium species.

Main Methods:

• Utilized electrochemical probes to monitor catalytic activity.
• Employed galvanic protection to inhibit palladium corrosion.
• Analyzed the dynamic phase changes during catalysis.

Main Results:

• Demonstrated that heterogeneous palladium(0) and homogeneous palladium(II) interconvert during vinyl acetate synthesis.
• Identified heterogeneous palladium(0) as an oxygen reduction electrocatalyst generating the potential for palladium(II) formation.
• Showed that homogeneous palladium(II) catalyzes ethylene acetoxylation, regenerating heterogeneous palladium(0).
• Observed reversible catalytic poisoning upon inhibition of palladium(0) to palladium(II) corrosion.

Conclusions:

• The catalytic cycle relies on dynamic phase interconversion between palladium(0) and palladium(II).
• This interconversion couples reactivity between material and molecular active sites.
• Highlights a new mechanistic perspective for catalytic processes involving phase changes.