Theoretical investigation into the effect of water on the N2O decomposition reaction over the Cu-ZSM-5 catalyst

Abstract

Copper exchanged zeolites are admirable catalysts for the direct decomposition reaction of harmful N₂O gas. However, the inhibition of the decomposition reaction in the presence of water vapor greatly limits their application. The present study discloses the mechanism for N₂O decomposition over dicopper active sites [Cu⋯Cu]²⁺ positioned at the opposite sides of the 10-membered ring in Cu-ZSM-5 by employing QM/MM calculations. The theoretical findings demonstrate the formation of [Cu–O–Cu]²⁺ and [Cu–O₂–Cu]²⁺ moieties during the decomposition of the first and second N₂O over dicopper active centers. Further, we have investigated the effect of water on the reaction steps, the possible intermediates, and the energetics of the direct decomposition of N₂O. The barrier for the dissociation step of O–N₂ involved in the water incorporating mechanism is significantly higher than the same reaction in the absence of water. The intermediate species [Cu–(OH)–Cu (OH)]²⁺ formed in the water incorporating pathway plays a crucial role in the inhibitory process of N₂O decomposition. The present study contributes to the understanding of the mechanism of various complex reactions involving N₂O and provides insights into the influence of water on other fields of heterogeneous catalysis.