The surface atomic oxyradical mechanism for Ag-catalyzed olefin epoxidation

We report comprehensive, quantitative, ab initio theoretical estimates for the energetics involved in the Ag-catalyzed epoxidation of olefins. From these estimates, a detailed mechanism is proposed. This mechanism (based on theoretical quantum chemical studies of the interaction of atomic and molecular adsorbates with clusters of Ag atoms) proposes that a surface atomic oxyradical anion is the active oxygen species for forming epoxide. This mechanism explains the role of electronegative (Cl^-) and electropositive (Cs⁺) promoters and explains why selectivity (toward epoxide) is far higher for ethylene than for propene and other higher olefins. Recent experiments which suggested O_2(ad) as the active species are reinterpreted within the context of this new atomic oxygen radical mechanism.