Revealing the evolution of CuII species and ammonia intermediates at 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 zeolites 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 °C), with the N₂ selectivity exceeding 90%. By exploring phase-resolved modulation excitation (ME) DRIFTS coupled with operando MS, we decoupled the reaction network, revealing a mechanism distinct from NH₃ activation that preferentially occurs on Cu²⁺–OH sites below 200 °C, but shifts to isolated Cu²⁺ sites above this threshold. Crucially, transient spectroscopy confirmed NH₃NO_x 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) reactions at high and low temperatures for slag-derived zeolites, establishing a robust mechanistic basis for scaling up cost-effective, waste-derived catalysts for NO_x abatement.