Revealing the evolution of Cu II species and ammonia intermediates under different temperatures for selective catalytic reduction of NO over cost-effective Cu-exchanged zeolite X catalysts

Abstract

Valorizing blast furnace slag (BFS) into high-performance environmental catalysts offers a sustainable “waste-to-treat-waste” pathway, yet understanding the active site dynamics on these complex low-silica Cu-based zeolite remains challenging. Here, we successfully upcycled BFS into Cu-exchanged zeolite X, where optimizing the Cu/Al ratio to 0.28 avoided framework collapse and achieved superior low-temperature selective catalytic reduction using ammonia (NH3-SCR) activity (>93% NO conversion at 150 oC) with N2 selectivity exceeding 90%. By exploring phase-resolved modulated excitation (ME) DRIFTS coupled with operando MS, we decoupled the reaction network, revealing a mechanism distinct from NH3 activation preferentially occurs on Cu2+-OH sites below 200 oC, but shifts to isolated Cu2+ sites above this threshold. Crucially, transient spectroscopy confirmed NH3NOx and NH2NO as the governing intermediates driving the reduction and oxidation half-cycles. These findings provide the evolution laws of reduction half-cycle (RHC) and oxidation half-cycle (OHC) reaction under high and low temperatures for slag-derived zeolites, establishing a robust mechanistic basis for scaling up cost-effective, waste-derived catalysts in NOx abatement.