Insight into the construction of multi-cavity micro-mesoporous SSZ-13: Dissolution, Al backfilling and framework reconstruction

The alkali leaching post-treatment method is a simple, economical and general route for introducing mesopores into SSZ-13, while the existing studies have rarely addressed the Al behavior between solution and zeolites framework during the alkali treatment. In this paper, a series of multi-cavity micro-mesoporous SSZ-13 were successfully prepared by using the alkali leaching post-treatment method at various treatment time. Extensive characterization illustrated that Al backfilling and zeolite framework reconstruction also existed during the NaOH treatment, besides the destruction of the zeolite framework due to the dissolution of Si and Al at the beginning of the reaction, and Al was preferentially backfilled into eight-membered ring (8 MR) to repair the zeolite framework and then filled into six-membered ring (6 MR) to reconstruct the zeolite framework. Concurrently, the amount of Brønsted acid (B acid) showed a decreasing-increasing-stabilizing trend during the progress. The catalytic activity and hydrothermal stability tests confirmed that multi-cavity micro-mesoporous SSZ-13 showed excellent catalytic activity for NH3 selective catalytic reduction (NH3-SCR) and good hydrothermal stability. This study provided basic guidance for the optimal design of the post-treatment alkali leaching route, which was highly significant for the development of hierarchically porous zeolites.