Alkaline–acid treated mordenite and beta zeolites featuring mesoporous dimensional uniformity

• Mesopore modification of MOR and BEA zeolites by alkali and acid treatments.
• Formation of mesopore structures featuring uniform pore size distributions.
• Hydrothermal alkali pre-etching promoting the micropore-inducing effect.

Zeolites with MOR and BEA structures were treated by alkaline and acid media to regulate mesoporous structures in dimensional uniformity. The mesoporous modification approach (viz. hydrothermal alkali pre-etching, bulk alkali leaching and posterior acid extraction) was demonstrated by the introduction of uniform mesopore structures into MOR and BEA crystals. Two modified zeolites with well preserving crystallinity and substantial mesoporosity exhibited the disordered but uniform BJH pore-distribution character. The dimensionally uniformizing tendency of mesopore formation is attributed to the reinforced micropore-inducing effect due to the combination of hydrothermal alkali etching with bulk alkali leaching of enhancing mass transport. In addition to the mesopore size uniformity the mesoporosity development is more available for BEA structure than for MOR structure. Moreover, the alkaline–acid modification method proposed can facilitate the adjustment on framework Si/Al ratio towards two topological zeolites.

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