Atomic-scale insights into zeolite-based catalysis in N₂O decomposition

Nitrous oxide (N₂O) has been the most serious ozone-depleting species throughout the 21st century. Zeolite-based catalysis is a highly promising method for N₂O removal in large-scale industrial applications. However, the exchanged transition metal species in zeolites greatly influence the performance of catalysts. The primary factor governing the catalytic activity is a fiercely debated topic and remains highly uncertain. Here we synthesize a series of transition-metal ion (Fe, Co, Ni, Cu)-exchanged ZSM-5 zeolite catalysts. Both experiments and density functional theory (DFT) calculations demonstrate that the activity for N₂O decomposition follows the order Fe ≈ Co > Ni > Cu. Analysis of the electronic structure properties reveals that the catalytic activity of the transition-metal ion-exchanged ZSM-5 zeolites is governed by the local softness of active sites and the composition of their HOMOs. The higher the local softness and the proportion of 4s orbitals in the HOMO, the higher the catalytic activity, which facilitates electron transfer in the redox process and thereby reduces the reaction barriers for N₂O decomposition into N₂ and O₂. Clarification of the nature of catalytic activity advances the understanding of the principles of zeolite-based catalysis, and is helpful for the design of highly efficient zeolite catalysts for pollutant removals.