Recent advances in zeolite science increasingly focus on the rational synthesis of hierarchical architectures and the determination of aluminum siting, both of which are essential for establishing structure–activity relationships in these catalytic materials. The present thesis addresses these challenges by providing fundamental insight into chemistry of post-synthetic leaching with a base, which is an increasingly industrially relevant strategy for the production of hierarchical zeolites, and by developing an accessible spectroscopic tool for aluminum siting in low-Al zeolites. 

The work first establishes in situ 27Al and 29Si MAS NMR spectroscopy as a probe of base leaching in zeolites. Using MFI as a model system, molecular-level information on the evolution of dissolved species during alkaline treatment is obtained, including determination of species responsible for controlled mesoporosity formation in MFI. The methodology is subsequently expanded through combined in situ NMR and in situ XRD studies of MFI and *BEA frameworks with varying Si/Al ratios, revealing how initial topology and composition govern leaching behavior. Complementary spatial insight is provided by ex situ TEM and EDX and in situ TEM, which directly visualize the formation of an aluminum-rich amorphous surface layer and support a dissolution–redeposition mechanism behind controlled mesoporosity formation in MFI. 

In a separate research direction, the thesis addresses the challenge of aluminum siting determination in low-Al zeolites. Using ex situ 29Si MAS NMR, descriptors for Al distribution are established for defect-free MFI materials. 

Overall, this work delivers molecular-scale understanding of hierarchical zeolite synthesis and introduces an NMR-based strategy for aluminum siting determination. The combined insights contribute to the rational design and characterization of advanced zeolitic materials for catalytic applications.