Activation of NO₂ by Modifying the Porphyrin Unit with Oxygen in a MnN₄ Graphene Layer

Abstract

In this article, the activation of NÀ O bonds in NO 2 molecules has been investigated by Density Functional Theory (DFT) calculations. Considering the graphene-based MnN 4 layer, nitrogen atoms in the porphyrin unit were sequentially replaced with oxygen atoms to create different MnN m O n /G (m + n = 4 and 1 < m � 4) layers. As more oxygen atoms are incorporated in porphyrin units for bare layers, the covalent character of the MnÀ O bonds is switched to the transit nature with respect to MnÀ N bonds. Moreover, the trend in bond strength decreasing in all oxygen-containing bonds is in line with the formation energy trends of bare layers. The same situation is also valid for the bonds between MnÀ N/O. For NO 2 adsorption configurations on all MnN m O n /G layers, NÀ O bonds in NO 2 are weakened by populating/depopulating antibonding/bonding orbitals, respectively. Even if the MnN 2 O 2 (hex)/G layer has a moderate NO 2 adsorption energy among the other layers, this layer provided the most significant activation over NÀ O bonds based on crystal orbital Hamilton population (COHP), crystal orbital bond index (COBI), and Atoms in Molecules (AIM) Bader Topological Analysis. Our results show that integrated COHP and integrated COBI values show a remarkable correlation with AIM-Bader parameters for the specific bonds which have descriptive capability over NO 2 molecule activation.