title: Size and Site Dependence of the Catalytic Activity of Iridium Clusters toward Ethane Dehydrogenation.
abstract: 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 Ir8is the least reactive toward H-elimination in ethane: Ir8+ C2H6→ H-Ir8-C2H5has 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 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-C2H5reaction is 3, 48, and 71 kJ/mol at the corner, edge, or face-center sites of the Ir18cuboid, 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+1/2O2→ Irn+ C2H4+ H2O. These results will be useful toward reducing the energy cost of ethane dehydrogenation in industry.
authors.affiliation: Department of Chemistry, Central Washington University , Ellensburg, Washington 98926, United States.
authors.forename: Yingbin
authors.initials: Y
authors.lastname: Ge
authors.affiliation: Department of Chemistry, Central Washington University , Ellensburg, Washington 98926, United States.
authors.forename: Hao
authors.initials: H
authors.lastname: Jiang
authors.affiliation: Department of Chemistry, Central Washington University , Ellensburg, Washington 98926, United States.
authors.forename: Russell
authors.initials: R
authors.lastname: Kato
authors.affiliation: Department of Chemistry, Central Washington University , Ellensburg, Washington 98926, United States.
authors.forename: Prasuna
authors.initials: P
authors.lastname: Gummagatta