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

The ion-exchanged Nd3+ significantly enhances the deNO x activity and low-temperature hydrothermal aging stability of Cu/SAPO-34 by stabilizing the zeolite framework and isolated Cu2+ ions. The NO x reaction rate of Cu/Nd-S-F is faster than that of Cu/S-F because of the formation of more active Cu2+ ions. [Display omitted] • The Nd-doping enhances the deNO x activity and low-temperature (70 °C) hydrothermal stability of Cu/SAPO-34 catalyst. • Cu/SAPO-34 exhibits poor low-temperature hydrothermal stability. • The active Cu2+ ions in Cu/SAPO-34 are partly transformed into unactive CuO under hydrothermal aging at 70 °C. • Nd3+ stabilizes the zeolite framework and isolated Cu2+ and combines with PO 4 3- to form NdPO 4. Designing a highly efficient and cost-effective deNO x catalyst for curbing NO x emission in diesel vehicle exhaust is highly desired but challenging. Herin, a Nd-promoted Cu/SAPO-34 (Cu/Nd-S) catalyst with superior NO x reduction efficiency and low-temperature hydrothermal stability was proposed. The NO x 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 H 2 -TPR results revealed that Nd3+ ions filled the defect sites of zeolites and combined with P species to form NdPO 4 , 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 NO x conversion. Meanwhile, in situ DRIFTS transient experiments elaborated that the NH 3 -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 NO x removal. [ABSTRACT FROM AUTHOR]