Employable Electrocatalysts: a DFT Investigation of NORR using Porphyrin-Based Transition Metal SACs

Nitric Oxide (NO) is an airborne pollutant released into the atmosphere by the combus- tion of fossil fuels. Its toxicity has short- and long term effects, including respiratory toxicity, DNA damage, and interference with the oxygen-delivery capacity of blood heme. Here, the reduction of Nitric Oxide to ammonia (NORR) by transition metal single atom cat- alysts within an unreactive porphyrin structure is examined theoretically. Density Func- tional Theory calculations are used to investigate the energetic relationships between reac- tion steps and to assess the overall catalytic ability of each catalyst. The adsorption and reaction pathways for NO reduction on a series of metalloporphyrin catalysts are iden- tified. Among several catalysts examined here, Cr-porphyrin emerges as the most likely NORR candidate, demonstrating exergonic adsorption of NO and minimum overpotential. The adsorption of NO is identified as the critical step, and the associated change in free energy is found to heavily influence the energy landscape of the overall reduction reaction. These insights establish Cr metalloporphyrins as potential NORR catalysts.