Mesoporogen-free synthesis of nanosized hierarchical ITQ-21 zeolites

Nanosized hierarchical zeolites are desirable for the reduction of diffusion limitations in catalysis. Herein, we report a cost-effective strategy for the synthesis of nanosized germanosilicate ITQ-21 zeolites with abundant intracrystalline meso/macropores upon modulating zeolite crystallization. Using quaternary ammonium N-cyclohexyl-N,N-dimethylcyclohexanaminium hydroxide as the organic structure-directing agent, nanosized hierarchical ITQ-21 zeolites have been successfully prepared in a concentrated gel system free of any mesoporogen or seed crystals. A possible mechanism based on aggregation followed by a ripening process is proposed. The as-prepared nanosized hierarchical Al-ITQ-21 zeolites show good catalytic activity for the acetal reaction of converting bulky substrates. This work provides a facile route upon modulating crystallization to generate intracrystalline mesopores in zeolite catalysts.