Engineering Al-Pair-Enriched Hierarchical Zeolites via D-6R SBU-Directed Aluminum Reorganization During Desilication

Alkaline desilication is commonly used to create hierarchical pores in zeolites but is often limited by dealumination and surface passivation, as leached aluminum (Al) species redeposit with silanol groups, leaving the framework Si/Al ratio largely unchanged. Here, we reveal a self-correcting Al migration mechanism in zeolites (SSZ-13, SSZ-39, Y, and AFX) only containing 4-membered ring(4R)-organized double-6-membered ring(D-6R) secondary building units (SBUs). During alkaline treatment, leached Al species dynamically reincorporate into the framework, mitigating passivation and enabling continuous desilication accompanied by significant Si/Al reduction. This process produces Al-pair-enriched hierarchical SSZ-39 with framework Si/Al ratio as low as 2-previously unattainable through conventional synthesis. Using SSZ-13 as a model, we identify a two-stage evolution: rapid desilication forming silica-alumina fragments, followed by Al migration that transforms isolated Al into paired Al species stabilized within SBUs under strong alkalinity. The resulting Al-rich SSZ-13/SSZ-39 zeolites and derivatives exhibit enhanced CO₂ adsorption and improved catalytic activity in Wacker oxidation and methanol-to-olefin reactions. This SBUs-directed Al redistribution creates high-silica hierarchical variants and establishes a general strategy to control porosity, Al distribution, and multifunctionality in zeolites for adsorption, ion exchange, and catalysis.