NOX reduction mechanism: Thermal vs electrochemical step

Abstract

Electrocatalysis could be a promising approach to produce valuable chemical compounds from carbon and nitrogen reactants. However, several challenges related to activity and selectivity need to be addressed to make these conversion energy and cost-efficient. The NO${}_{\text{X}}$${}_{\text{X}}$ reduction is an important reaction for denitrification and here we elucidate how the reaction mechanism controls the product distribution. We investigated the reduction reaction on a series of transition metals (Cu, Ni, Co, Fe, and Mn) to understand the factors governing the associative and dissociative reaction paths. While Cu favors the associative protonation path, the NO${}_3^{-}$${}_3^{-}$ and NO${}_2^{-}$${}_2^{-}$ reduction on Ni, Co, Fe, and Mn surfaces favor the dissociative reaction pathway. Comparing our DFT computed results with experimental data we found that apart from competing HER the adsorption of *NO₂ and its N-O dissociation barrier are two key factors for selective NO${}_3^{-}$${}_3^{-}$ reduction towards ammonia and NO${}_2^{-}$${}_2^{-}$. These strategies could be extended to understand energetically robust reactions like N${}_2$${}_2$ and CO${}_2$${}_2$ reduction reactions.