Mechanism of catalyzed graphite oxidation by monolayer channeling and monolayer edge recession

Monolayer channeling (i.e., channeling at one graphite layer depth) on the basal plane of graphite is revealed for catalysts in the graphite-oxygen reaction by employing gold decoration/TEM. Rates and mechanisms of monolayer channeling have been studied for Pt, Cu, V, and V₂O₅. The breakage of carbon-carbon bonds at the Pt and edge graphite interface is the rate-limiting step for Pt-catalyzed oxidation. An oxygen transfer mechanism appears to be operative in the vanadium-catalyzed oxidation, and the rate-limiting step is the oxidation of the surface of the particle which is in the reduced state of V₆O₁₃. The rate-limiting step for the copper-catalyzed reaction is a step occurring at the interface between the catalyst and edge graphite, either by the breakage of carbon-carbon bonds or the oxidation of edge carbon by CuO. Vanadium oxide also undergoes catalyzed monolayer edge recession, forming elongated hexagonal etch pits which are bound by (1120) (zig-zag) edges. It is shown that there are two different graphite zig-zag steps exhibiting different reactivities which result in the unique shape of the pits. By comparing the monolayer channeling rates with the rates for deep-layer channeling reported in the literature, it is concluded that the relative contribution to the total oxidation rates by monolayer channeling is at least as important as that by deep channeling.