Electrochemical Phase Interconversion Enables Homogeneous-Heterogeneous Bifunctionality in Pd-Catalyzed Vinyl Acetate Synthesis

Current mechanistic paradigms in catalysis generally hold that a catalytic cycle is carried out by either a homogeneous or heterogeneous active species. Herein, we show that a prominent industrial process, palladium-catalyzed vinyl acetate synthesis, proceeds via interconversion of heterogeneous Pd(0) and homogeneous Pd(II) during catalysis, with each species playing a complementary role. Using electrochemical probes, we find that heterogeneous nanoparticulate Pd(0) serves as an active oxygen reduction electrocatalyst to furnish the high driving force required for corrosion to form homogeneous Pd(II), which then catalyzes selective ethylene acetoxylation with re-formation of heterogeneous Pd(0). Inhibiting the corrosion of Pd(0) to Pd(II) by galvanic protection results in reversible poisoning of catalysis, highlighting the essential role of phase conversion in this catalytic cycle. These results challenge the tacit assumption that catalysis proceeds via either homogeneous or heterogeneous modes, and instead highlights how dynamic phase interconversion can serve to harness and couple complementary reactivity across molecular and material active sites.