Effect of Ligand Chemistry on the Electronic Properties and Reactivity of Cobalt Acetate Autoxidation Catalysts

Arun Asundi, Amani Ebrahim, Anjani Maurya, Chad Palumbo, Kevin Sullivan, Gregg Beckham, Ritimukta Sarangi

Research output: Contribution to journalArticlepeer-review

1 Scopus Citations

Abstract

Autoxidation chemistry catalyzed by cobalt(II) acetate is an industrial pathway for converting hydrocarbons into oxygenated compounds and has promising potential applications in plastic waste deconstruction. However, the chemical properties of the Co acetate-based catalysts and their roles in the reaction mechanism are poorly understood, and as a result, attempts to redesign the autoxidation chemical process for novel applications lack clear direction. In this work, we investigate the structure and electronic properties of a series of multinuclear Co(III) compounds that have been proposed as active participants in catalytic autoxidation. Through a combination of X-ray spectroscopic measurements [Co K-edge X-ray absorption spectroscopy (XAS), extended X-ray absorption fine structure (EXAFS), Kβ X-ray emission spectroscopy (XES), and high-energy-resolution fluorescence detection (HERFD) XAS] and theoretical methods, we characterize the interactions of Co with acetate and hydroxyl ligands in these compounds. We show that the substitution of acetate ligands with hydroxyls in these compounds causes an increase in the electron density on Co, driven by the loss of a π back-bonding interaction between Co and acetate and an increase in electron donation to Co from the hydroxyl ligands. We further classify the bonding between Co and acetate based on the orbital overlap and show that the experimental absorption and emission spectra are well-described by the resulting molecular orbitals. Finally, we predict the impacts of acetate/hydroxyl ligand exchange on autoxidation catalytic properties, showing that the reaction free energies for key Co oxidation and reduction steps are extremely sensitive to metal-ligand bonding interactions and thus have meaningful impacts on overall reactivity. The results of this study constitute an important set of design criteria for developing novel homogeneous autoxidation catalysts.

Original languageAmerican English
Pages (from-to)15797-15808
Number of pages12
JournalJournal of Physical Chemistry C
Volume127
Issue number32
DOIs
StatePublished - 2023

Bibliographical note

Publisher Copyright:
© 2023 American Chemical Society.

NREL Publication Number

  • NREL/JA-2A00-87230

Keywords

  • acetate ligands
  • autoxidation
  • Co acetate-based catalysts
  • multinuclear Co(III) compounds
  • X-ray spectroscopic

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