C-H bond activation by Irn and Rhn (n = 8, 12, 18) nanoclusters has been studied using the B3LYP method with Grimme’s D3BJ dispersion correction. The goal is to find catalysts that are thermodynamically stable and that can convert alkanes to alkenes efficiently. The cubic or cuboid structures of the Ir clusters are thermodynamically stable and have extraordinary catalytic abilities towards the C-H bond activation of ethane. Their catalytic abilities strongly depend on the cluster size and the site where the catalysis occurs. Cubic Ir8 (2×2×2 lattice) breaks a C-H bond on ethane with a 64 kJ/mol energy barrier, while Ir12 (3×2×2 lattice) and Ir18 (3×3×2 lattice) break C-H with energy barriers as low as 22 kJ/mol and 3 kJ/mol, respectively. The site-dependence is as prominent as the size effect for the reaction: the energy barrier for the Ir18 + C2H6 → H−Ir18− C2H5 reaction is 3 kJ/mol, 48 kJ/mol, or 71 kJ/mol when the C-H bond breaks on a corner, edge, or face-center Ir atom, respectively. The cubic or cuboid structures of the Rhn clusters also exhibit strong catalytic abilities towards C-H bond activation. For example, the Rh18 + C2H6 → H−Rh18− C2H5 reaction is virtually barrier-less at the corners of the Rh18 cuboid structure. However, it remains unclear whether the Rhn (n = 8, 12, 18) clusters prefer to adopt the cubic or cuboid structures as the Irn clusters do. The answer is likely “no” as the preliminary calculations on Rh8 suggest that the bi-capped trigonal prism may have lower energy than the cubic structure. We will continue searching for the most stable structures of the Rhn clusters and then study their catalytic abilities towards the C-H bond activation.

B3LYP study of the dehydrogenation of ethane catalyzed by iridium and rhodium clusters

255th National Meeting (2018)

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