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. Zeolitebased 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 approximate to 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 N-2 and O-2. 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. (C) 2019 Elsevier B.V. All rights reserved.