Methane Activation by CoOₘⁿ⁺ (n = 0, 1, 2; m= 1, 2): Reactivity Parameters, Electronic Properties and Binding Energy Analysis
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The need for renewal, more efficient and conscious usage of energy resources has led to a great interest in carrying out studies aiming to find novel sources of energy, which are able to supply the growing global demand, and at the same time, providing an ecofriendly usage of natural resources. In this context, the usage of methane stands out as a promising energetic alternative for this goal, mostly due to the existence of vast reserves, its low cost and less polluting fuel. For theoretical calculations B3LYP, CCSD(t) and ZORA-B3LYP methods were used to look into the catalytic properties of (CoOₘⁿ⁺ n= 0, 1, 2 and m=1, 2) in the methane C-H bond activation. According to the EDA outcomes, the studied species presented two stabilizing factors for the global interaction energy, being the electrostatic ΔEelstat and orbital ΔEorb interactions. The HOMO and LUMO orbitals were also evaluated based on the molecular orbital diagrams for the monoxides and dioxides series. Regarding the oxidative insertion mechanism, the outcomes demonstrate that the initial interaction between oxide and methane is of great relevance in its activation process, in which EBonding is benefited by the increasingly charge on the central metal. The high electron density regarding the oxides is meaningful for the reaction kinetics and the oxo ligands influence the thermodynamics of the reaction, becoming the DHA mechanism exergonic. Regarding the OHM mechanism, better kinetic conditions are found for CoO2++ and better thermodynamics for doubly charged cobalt monoxides and dioxides.