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Atomic layer deposition (ALD) of Ni on the metal–organic framework NU-1000 has been shown to generate a material that serves as a catalyst for ethylene dimerization. However, the precise nature of the active catalytic site or sites remains uncertain. Here we employ periodic density functional calculations to characterize the structure and reactivity of the deposited species. Optimized lattice constants for a sequence of structures incorporating successively more Ni4-hydroxo clusters in the c pore of NU-1000 show good agreement with experimental trends involving multiple ALD cycles; therefore we study the catalytic cycle for this cluster in detail, and we compare it to that for a site with only a single Ni atom. We find that both the atomic Ni catalyst and the Ni4-hydroxo cluster have higher catalytic activity in the singlet state than in the triplet state. We also find that the two catalysts have very similar activity. Thus, precise size control of the active catalytic species is not essential for ethylene dimerization in this system.
Bibliographical noteFunding Information:
This work was supported as part of the Inorganometallic Catalyst Design Center , an EFRC funded by the DOE, Office of Basic Energy Sciences ( DE-SC0012702 ). We thank Aaron League for many helpful discussions. The computations were performed at the Minnesota Supercomputing Institute and the Environmental Molecular Sciences Laboratory (EMSL) under project st48848.
© 2017 Elsevier Inc.
- Density functional theory
- Ethylene dimerization
- Metal−organic framework
- Ni catalyst