Mechanistic Understanding of the Effect of Active Site Size in the Dehydrogenation of Ethane on Highly Dispersed Co/SiO2 Catalyst
- Type: Conference Presentation
- Conference Type: AIChE Annual Meeting
- Presentation Date: November 11, 2021
- Duration: 15 minutes
- Skill Level: Intermediate
- PDHs: 0.50
This paper investigates differences in catalytic activity of the two types of sites and attempts to uncover unexplored theoretical efficiencies in earth-abundant 3d and 4d metals for small alkane dehydrogenation. We map out catalytic pathways using density-functional theory (DFT) calculations, rank them in kinetic importance using micro-kinetic analysis and validate them by comparing with experimental data.
We show that, contrary to what has been suggested in literature1, the rate-limiting step on the catalytically dominant pathway on sub-nanometer Co(II) oxide clusters is the second C-H bond activation. Informed by this development, we explore modulation of the reaction rate by varying the metal center.
We argue that on the dominant pathway on atomically dispersed Co(II) sites, the second C-H activation step entails a spin crossover. We use the Landau Zener model and non-adiabatic transition state theory to evaluate rate constants. We compare with other single-site metal species (Ga/Al2O3) with fully filled d orbitals.
Finally, we will present a comparison between the mechanisms (and corresponding barriers) on the two types of active sites and discuss implications for related metal ions with partially filled d-orbitals (Fe, Ni).
1 Estes, D. P. et al. J. Am. Chem. Soc. 138, 14987-14997, (2016).
2 Lee, S. et al. Nat. Commun. 10, (2019).
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