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This research focuses on optimizing transition metal nanocatalyst immobilization and activity to enhance ethane dehydrogenation. Ethane dehydrogenation, catalyzed by thermally stable Irn (n = 8, 12, 18) atomic clusters that exhibit a cuboid structure, was studied using the B3LYP method with triple-ζ basis sets. Relativistic effects and dispersion corrections were included in the calculations. In the dehydrogenation reaction Irn + C2H6 → H−Irn−C2H5 → (H)2−Irn−C2H4, the first H-elimination is the rate-limiting step, primarily because the reaction releases sufficient heat to facilitate the second H-elimination. The catalytic activity of the Ir clusters strongly depends on the Ir cluster size and the specific catalytic site. Cubic Ir8 is the least reactive towards H-elimination in ethane: Ir8 + C2H6 → H−Ir8−C2H5 has a large (65 kJ/mol) energy barrier, whereas Ir12 (3×2×2 cuboid) and Ir18 (3×3×2 cuboid) lower this energy barrier to 22 kJ/mol and 3 kJ/mol, respectively. The site dependence is as prominent as the size effect. For example, the energy barrier for the Ir18 + C2H6 → H−Ir18−C2H5 reaction is 3 kJ/mol, 48 kJ/mol, and 71 kJ/mol at the corner, edge, or face-center sites of the Ir18 cuboid, respectively. Energy release due to Ir cluster insertion into an ethane C–H bond facilitates hydrogen migration on the Ir cluster surface, and the second H-elimination of ethane. In an oxygen-rich environment, oxygen molecules may be absorbed on the Ir cluster surface. The oxygen atoms bonded to the Ir cluster surface may slightly increase the energy barrier for H-elimination in ethane. However, the adsorption of oxygen and its reaction with H atoms on the Ir cluster releases sufficient heat to yield an overall thermodynamically favored reaction: Irn + C2H6 + ½ O2 → Irn + C2H4 + H2O. These results will be useful towards reducing the energy cost of ethane dehydrogenation in industry.


This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry A, copyright © 2016 American Chemical Society after peer review. To access the final edited and published work, click here.


Journal of Physical Chemistry A


Copyright © 2016 American Chemical Society

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