In recent years, Zr-based metal organic frameworks (MOFs) have revealed their potential for heterogeneous catalytic applications. Recently, the installation of Co(II) ions to the Zr6 nodes of the MOF NU-1000 has been successfully achieved. Cobalt decorated NU-1000, upon activation in a flow of O2 at 230 °C, has been shown to catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. A density functional theory (DFT) study of Co decorated NU-1000 catalyzed propane ODH process using a cluster model containing one Co atom has been carried out, elucidating the reaction mechanism. However, polynuclear sites may also be competitive for this reaction; in this regard, the mechanism of the ODH with a two Co atoms model has been analyzed, demonstrating the C-H activation of propane to be the rate determining step. Furthemore, the effect of doping one of the two cobalt atoms on this step of the catalytic cycle with other transition metals using DFT has also been analyzed. After this work, the question of whether DFT is accurate enough to describe the challenging electronic structure of these systems arose. We used multiconfigurational quantum methodologies to analyze the electronic structure of the bimetallic cluster model, with one cobalt and the second metal being Zn, Cu, Ni, Co, Fe, Mn and Ti. We noticed substantial differences with respect to DFT in the oxidation states of some of the metals and in the oxygen spin densities. This can in turn switch the C-H abstraction mechanism from a hydrogen atom to a proton coupled electron transfer (which is not well captured by DFT). We then analyzed the reaction energies of the C-H bond activation, and found sizable differences with respect to DFT, pointing out the challenge of accurately modeling these catalytic systems. A further comparison of multireference calculations with a series of exchange-correlation functionals will be discussed.

Multiconfigurational calculations on bimetallic decorated NU-1000 for C–H activation and comparison with DFT

2019 Fall National Meeting

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