CNT-Catalyzed Oxidative Dehydrogenation of Ethylbenzene to Styrene: DFT Calculations Disclose the Pathways

Oxygen atoms, in the form of epoxy or carbonyl groups present at the edges of carbon nanotubes, trigger oxidative dehydrogenation of ethylbenzene to styrene. DFT calculations reveal that the process can occur along three pathways. The first two bifurcate from the initial transformation of an epoxide into a hydroxyl group, which occurs via a biradical transition state and the formation of a benzyl-like intermediate. The epoxide can further react to release styrene and form a water molecule, as observed experimentally, via a highly exothermic process. Alternatively, in the presence of a second adjacent epoxide, styrene is also produced without water formation along a less exothermic pathway that leaves two hydroxyl groups on the nanotube surface. Along the third pathway, two adjacent carbonyl groups (quinone functionality) also promote the formation of styrene, with energy barriers similar to those calculated in the presence of epoxy groups. These are in the range 36–37 kcal mol −1 . These values that can be easily surmounted at the working temperature used in the experiment (between 450 and 550 °C).