Unraveling Cu Speciation Dynamics and Framework Stability in High-Si LTA Zeolites via <i>In Situ</i> X-ray Absorption Spectroscopy

The limited thermal stability of Cu-based zeolite catalysts remains a major challenge for lean NOx after treatment under extreme exhaust conditions. Here we show that Cu/LTA with a Si/Al ratio near 20 and optimized Cu loading combines nearly full NOx conversion with good hydrothermal stability even after aging up to 900 °C. In situ temperature-dependent X-ray absorption spectroscopy captures the progressive evolution of Cu species during thermal activation in oxidizing environments, revealing that mobile Cu(II) ions gradually dehydrate to form Z2Cu(II) and ZCu(II)OH, with partial conversion of the latter into Cu(I). Upon high-temperature hydrothermal aging, the Cu speciation shifts toward Z2Cu(II), consistent with enhanced framework stabilization and the suppression of bulk CuO formation. A qualitative wavelet-transform EXAFS analysis further evidences the emergence of proximal Cu sites, indicating increased structural connectivity between copper centers. These results unravel the dynamic redox and coordination behavior of Cu species in high-silica LTA and establish Cu/LTA as a hydrothermally resilient NH3-SCR catalyst, clarifying how framework stability and Cu speciation interplay to sustain long-term catalytic performance. This work sheds light on the role of Cu speciation and its dynamic evolution in governing the hydrothermal stability of Cu/LTA catalysts and provides a rational framework for the design of durable Cu-based zeolite catalysts for NH3-SCR under harsh exhaust conditions.