Comprehensive exploration of high-temperature hydrothermal aging impact on Cu-SSZ-13 catalyst reaction mechanisms and performance optimization strategies
摘要
High-temperature hydrothermal aging (700 and 800 °C, 16 h) was applied to Cu-SSZ-13 to evaluate its NH₃-SCR durability. Fresh catalyst keeps NOₓ conversion > 90% (200–500 °C) and N₂ selectivity > 95%, whereas 800 °C-aged sample peaks at only ~ 80% NOx conversion and 91.5% N2 selectivity at 600 °C. NH₃-TPD shows total acidity falling to 70%, with Brønsted-bound NH4⁺ strongly suppressed. XRD, BET, SEM and TEM evidence partial (700 °C) or severe (800 °C) CHA framework collapse, surface area dropping from 450 to 391 m2 g⁻1, pore volume shrinking to 0.14 cm3 g⁻1, and Cu-oxide clusters forming. In-situ DRIFTS indicates that aged surfaces still follow the standard SCR mechanism: NH3 adsorbs on residual Lewis and Brønsted sites, NO + O2 generates mainly bidentate and bridged nitrates, and bridged nitrates react with adsorbed NH₃ first. The primary aging routes are H2O-driven de-alumination that eliminates Brønsted acid sites and hydrolysis of [Cu(OH)]⁺ into less-active CuxO species, while Cu2⁺ in six-ring sites partly re-covers after cooling. These findings confirm that hydrothermal damage is mainly structural rather than mechanistic, providing a clear target—stabilising acid sites and Cu dispersion—for designing anti-aging Cu-SSZ-13 catalysts in diesel after-treatment.