Abstract: A series of modified HEU-1 zeolites were prepared using hydrochloric acid treatment, hydrothermal treatment, and a combination of these. The parent and modified HEU-1 zeolites were characterized by X-ray diffraction, N₂ adsorption-desorption isotherms, X-ray fluorescence, temperature-programmed desorption of ammonia, Fourier-transform infrared spectroscopy of adsorbed pyridine, and ²⁷Al solid-state magic-angle spinning nuclear magnetic resonance techniques. The catalytic cracking performances of the modified HEU-1 zeolites were evaluated on a fixed-bed microreactor at 625 °C, atmospheric pressure, and an n-hexane weight hourly space velocity of 2.0 h⁻¹. The results showed that extra-framework alumina could be removed by directly treating with hydrochloric acid, and framework alumina could be removed by hydrothermal treatment. Acidity characterization showed that the weak acid sites of HEU-1 zeolites could be adjusted using acid treatment, and the number of strong acid sites could be reduced using hydrothermal treatment. The framework n_Si:n_Al ratio was improved by using a combination of hydrothermal treatment and acid leaching. The acidities of the HEU-1 zeolites were adjusted and both the mesopore volume and external surface area were enhanced. In n-hexane cracking reactions, the dealuminated HEU-1 zeolite obtained by hydrothermal treatment for 4 h at 600 °C and then washing with hydrochloric acid exhibited the highest propylene production as a result of suppression of the hydrogen transfer reaction. At 625 °C, the selectivity for propylene on HEU-1(HT4-HCl) increased to 35.2% from 21.9%, and the lifetime of HEU-1(HT4-HCl) was also prolonged from not more than 10 to 40 h.

Key words: HEU-1 zeolite, dealumination, hydrothermal treatment, hydrochloric acid treatment, catalytic cracking, propylene