Synthesis and characterization of hierarchical Y zeolites using NH4HF2 as dealumination agent

In this work, the hierarchical Y zeolites are firstly obtained by etching NaY zeolites with different NH4HF2 solutions. The morphology and microstructure, toluene adsorption property of as-prepared hierarchical Y zeolites are characterized. The results demonstrate that the mesoporous number and size, the n(SiO2)/n(Al2O3) value of hierarchical Y are increased with NH4HF2 concentration. The 0.3M NH4HF2-etched NaY exhibits satisfactory crystallinity, suitable mesoporous content and better toluene adsorption performance. The NH4HF2-etched NaY is an excellent material for pressure swing adsorption. Furthermore, the synthesis mechanism of hierarchical Y has been elaborately demonstrated. The synergistic effect of H+ and F− is beneficial to dealumination as well as the introduction of mesoporous. The NH4HF2 ionizes into positive H+ and negative F− at a very slow rate, which avoids the concentration of H+ and F− going up suddenly. Under the circumstances, the dealumination reaction between NH4HF2 and NaY zeolites is more sustained and mild, and the crystallinity of hierarchical Y zeolites is higher than that of the HCl/NH4F-etched or HF/NH4F-etched NaY. This work presents an effective method to synthesize the hierarchical Y zeolites.