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Unraveling the Reaction Mechanism for Nickel-Catalyzed Oxidative Dehydrogenation of Ethane by DFT: The C–H Bond Activation Step and Its Following Pathways

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journal contribution
posted on 09.02.2012, 00:00 by Xufeng Lin, Yanyan Xi, Jian Sun
Understanding the reaction mechanism for oxidative dehydrogenation (ODH) of alkanes, especially the key intermediate­(s) that generates alkene is essential for designing good ODH catalysts. To unravel the mechanisms for Ni-based oxide-catalyzed ODH reactions, we investigated the reactions of C2H6 with Ni3Ox (x = 1, 2, 3) clusters by density functional calculations. For Ni3O3, three pathways were examined for the C–H bond activation step, and the one with concerted mechanism undergoing at two sites is the most favorable pathway, producing an ethylnickel species. Then, four reaction pathways, namely, β-H elimination, α-H abstraction, C–C bond cleavage, and isomerization to an ethoxide species, with 11 reaction channels, were examined to understand the behavior of this ethylnickel species. The selectivity of C2H4 (SC2) for this reaction was calculated based on the relative rates of these four pathways. Similar investigations were carried out on the reactions of Ni3O2 and Ni3O1 clusters with C2H6. The calculated SC2 increases from ∼37 to over 99% with decreasing x value in Ni3Ox.