Facile synthesis of hierarchical T-type zeolites with parallel-aligned rod-like nanocrystals

Hierarchical T-type zeolites (HT zeolites) with parallel-aligned rod-like nanocrystals (∼73 nm in width) were synthesized via a facile method simply by regulating the SiO₂/Al₂O₃ molar ratio and crystallization kinetics. Selected area electron diffraction (SAED) analysis revealed that the crystallographic growth direction of the nanorods was along the c-axis while the short axis was along a- and b-directions. The optimized HT zeolites exhibited a framework Si/Al ratio of 2.74 and a high BET surface area (489.6 m²/g). The SiO₂/Al₂O₃ molar ratio in the synthesis gel critically influenced zeolite structure, particle size, and morphology, inducing a competing CHA phase with a walnut-shaped morphology with lower ratio of 8. Highly crystalline HT zeolites were obtained at 373 K after 48 h, following an S-shaped crystallization curve, where rod-like nanocrystals grew in a parallel alignment while maintaining nearly constant widths. To investigate the nucleation and crystal growth behavior, Gualtieri model analysis and time trace experiments at different temperature were further conducted. The activation energies for nucleation and crystal growth, calculated from the Arrhenius relationship in the temperature range of 353–403 K, were found to be 43.0 ± 3.2 and 36.5 ± 1.7 kJ mol⁻¹ respectively, indicating nucleation was the rate-limiting step. The HT zeolites exhibited a CO₂ adsorption capacity of 4.01 mol/kg at 1 bar and 273 K, with CO₂/N₂ initial and final adsorption ratios of 40.4 and 5.4, respectively. This work presents a simple and effective method for preparing hierarchical T zeolites, which can serve as a possible reference for the design of other hierarchical materials.