Improving the hydrothermal stability of Al-rich Cu-SSZ-13 zeolite via Pr-ion modification

Al-rich (Si/Al = 4-6) Cu-SSZ-13 has been recognized as one of the potential catalysts to replace the commercial Cu-SSZ-13 (Si/Al = 10-12) towards ammonia-assisted selective catalytic reduction (NH₃-SCR). However, poor hydrothermal stability is a great obstacle for Al-rich zeolites to meet the catalytic applications containing water vapor. Herein, we demonstrate that the hydrothermal stability of Al-rich Cu-SSZ-13 can be dramatically enhanced via Pr-ion modification. Particularly, after high-temperature hydrothermal aging (HTA), CuPr_1.2-SSZ-13-HTA with an optimal Pr content of 1.2 wt% exhibits a T₈₀ (temperature window of NO conversion above 80%) window of 225-550 °C and a T₉₀ window of 250-350 °C. These values are superior to those of Cu-SSZ-13-HTA (225-450 °C for T₈₀ and no T₉₀ window). The results of X-ray diffraction Rietveld refinement, electron paramagnetic resonance (EPR) and spectral characterization reveal that Pr ions mainly located in the eight-membered rings (8MRs) in SSZ-13 zeolite can inhibit the generation of inactive CuO during hydrothermal aging. This finding is further supported by density functional theory (DFT) calculations, which suggest that the presence of Pr ions restrains the transformation from Cu²⁺ ions in 6MRs into CuO, resulting in enhanced hydrothermal stability. It is also noted that an excessive amount of Pr ions in Cu-SSZ-13 would result in the production of CuO that causes the decline of catalytic performance. The present work provides a promising strategy for creating a hydrothermally stable Cu-SSZ-13 zeolite catalyst by adding secondary metal ions.