Direct incorporating small amount of Ce (III) in Cu-SAPO-18 catalysts for enhanced low-temperature NH₃-SCR activity: Influence on Cu distribution and Si coordination

The reduction of NO_x emission during the cold start period of diesel vehicles requires special attention in accordance with the emission regulations. In this work, the direct incorporation of cerium and copper in SAPO-18 catalyst with AEI type framework structure (CuCe-SAPO-18) resulting in a substantial enhancement of the performance in the low-temperature NH₃-SCR reaction (<200 ℃). A small amount of cerium (0.13–0.31 wt%) broadened the reaction temperature range of use and increased the hydrothermal stability of the catalyst considerably. The cerium species was introduced in the ion-exchange sites of Cu-SAPO-18 in the form of Ce³⁺ ions even with high loading (3.15 wt%). The Ce³⁺ ions were found to affect the distribution of silicon and aluminum atom coordination (²⁹Si NMR, ²⁷Al MAS NMR) in the AEI-type skeleton structure leading to an increase of both the amount of active Cu²⁺ species and the acidity of the CuCe-SAPO-18 catalysts that are beneficial for the NH₃-SCR reaction.