Correlation of the changes in the framework and active Cu sites for typical Cu/CHA zeolites (SSZ-13 and SAPO-34) during hydrothermal aging

The relative framework stability of Cu/CHA zeolites (SAPO-34 and SSZ-13) was studied during hydrothermal aging at 800 degrees C, and the fundamental mechanism for the framework change was investigated. Additionally, the relationship between the variation in the framework and active SCR reaction sites was established. SAPO-34 showed stronger stability during hydrothermal aging than SSZ-13. The results showed that dealumination occurred in the SSZ-13 zeolite, leading to the loss of crystallinity and a severe decrease of the Bronsted acid sites. Simultaneously, the detached Al(OH)(3) species deactivated the Cu species by the transformation of isolated Cu2+ ions to CuAlOx sp ecies. While the vacancy in the SAPO-34 framework caused by desilication could be healed with the migration of extra-framework Al and P atoms to the defects. And the Cu species showed a certain degree of aggregation with the improved redox ability of the aged Cu/SAPO-34 zeolite and the acidic properties were well maintained.