New insights into the effects of Nd on low-temperature hydrothermal stability of deNOx Cu/SAPO-34 catalysts: A comparative evaluation of the mechanism

Designing a highly efficient and cost-effective deNOx catalyst for curbing NOx emission in diesel vehicle exhaust is highly desired but challenging. Herin, a Nd-promoted Cu/SAPO-34 (Cu/Nd-S) catalyst with superior NOx reduction efficiency and low-temperature hydrothermal stability was proposed. The NOx conversion of fresh Cu/Nd-S-F at 200 °C was improved to 86.1 % compared to fresh Cu/S-F (78.1 %). XRD and H2-TPR results revealed that Nd3+ ions filled the defect sites of zeolites and combined with P species to form NdPO4, thus stabilizing the zeolite framework and maintaining the stability of active copper species. The interaction between Nd3+ ions and Cu2+ ions protected the active copper species (Cu2+-2Z and [Cu(OH)]+-Z) from the attack of low-temperature (70 °C) moisture. However, Cu/SAPO-34 suffered from the rapid and irreversible deterioration under 70 °C of water bath, leading to the loss of surface Brønsted acid sites (Al-(OH)-Si) and isolated Cu2+ ions, so aged Cu/S-70 exhibited inferior NOx conversion. Meanwhile, in situ DRIFTS transient experiments elaborated that the NH3-SCR reaction over Cu/SAPO-34 and Cu/Nd-SAPO-34 catalysts obeyed the E-R and L-H routes simultaneously. To be noted, the Nd-doping engineering afforded a promising strategy for boosting the low-temperature hydrothermal stability of Cu/SAPO-34 catalysts for the practical application of NOx removal. © 2024 Elsevier B.V.