A grand challenge within the catalyst community is developing industrially-relevant catalysts with high activity, selectivity, and recyclability. One promising solution is a metal complex (i.e., a 3d transition metal such as Nickel(II)) anchored to a porous support since such materials feature well-defined, uniform, and isolated active-sites. Depending on the reaction environment, these supported metal cation complexes exhibit structural changes that affect catalytic performance. To reach their full-potential as catalytic materials, fundamental insights into the relationship between reaction environment, structure, and performance are required. However, the molecular-level changes to structure as a function of reaction conditions are challenging to elucidate, even using state of the art in operando techniques. Hence, complementary descriptions of the system, which can be provided by simulations, are needed. In this work, we use density functional theory (DFT) calculations and ab initio thermodynamic modeling to learn how the reaction environment influences Ni(II) complex catalysts supported on the metal-organic framework (MOF) NU-1000. We investigate more than 300 different compositions and morphologies in order to reveal those that are favorable at relevant activation and reaction conditions. Activation conditions with high hydrogen partial pressure reduce the Ni atoms from Ni(II) to Ni(0) indicating that thermodynamically the cluster favors metal nanoparticle (NP) formation. Slightly decreasing the hydrogen partial pressure expunges water molecules to produce intermediate activate structures with undercoordinated Ni(II) atoms that competes thermodynamically with the NP formation. In all, we explore the influences that conditions related to catalytic activation, catalytic ethylene hydrogenation, and catalytic ethylene oligomerization have on the Ni(II) complexes. For each, we demonstrate the difference between the “as-synthesized” and the operational active site. The computational approach demonstrates how the catalyst structure is tunable using temperature and partial pressure to control the morphology and composition. The findings establish thermodynamically relevant models that require further computational catalytic investigations as well as showcasing how to tune structures using different reaction conditions.

Identifying the morphology and composition of actives sites in a heterogeneous metal cation complex catalyst supported on NU-1000

ACS Spring Meeting 2021

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