Bridging catalysis

The team first analysed a model liquid phase system for this reaction, composed of acetic acetic-potassium acetate solution with Pd/C, and found that Pd(0) is subjected to corrosion by molecular oxygen. This allows the solubilization of the metal as Pd(II) acetate, with the Pd(II) species then reacting with ethylene to yield VA and metallic Pd(0) as precipitate. They also notice that Pd/C promotes the reaction better than bulk Pd. They also found this is valid also for the electrochemical and thermochemical processes of model VA production in the absence of O₂: in all cases, the Pd(II) species is solvated from the solid support upon a corrosion event, but the Pd reoxidation is a heterogeneous process upon which Pd(0) particles are dispersed on the support, as confirmed by TEM measurements, ready for the subsequent corrosion step in the next catalytic cycle. Finally, the same electrochemical behaviour is also observed in a model system of the process’ industrial conditions.

Surendranath and co-workers’ investigations point to a dynamic interplay between heterogeneous Pd(0) and homogenous Pd(II) species, with a catalytic system that challenges the current catalytic phase separation paradigm, highlighting the intricate relationship between homogeneous and heterogeneous modes of reaction.