Impact of Edge Oxidation State on Red-Ox Barriers during Hydrocarbon Oxydehydrogenation over Carbon Nanotube Catalysts: A Theoretical Study

A computational investigation of the oxidative dehydrogenation (ODH) of hydrocarbons over model edge-oxidized carbon nanotubes (CNTs) providing different degrees of CO/C–OH surface termination (i.e., reduction) was performed. The pool of gaseous species is assumed to contain the initial reagents (hydrocarbons, O2) and volatile intermediates (R•, HO2 •, HO•, H2O2). The barriers of both the H-abstraction from the substrate molecules by surface carbonyl groups as well as of the reoxidation of hydroxyl groups sensitively respond to the red-ox state of the model cluster. Accordingly, the surface state of CNT catalysts under ODH steady-state reaction conditions represents an intermediate degree of catalyst reduction. This conclusion agrees with previously published kinetic and in situ XPS studies of carbon-catalyzed ODH.