Abstract: USY molecular sieves before and after ammonium fluoride modification were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption, 27Al solid nuclear magnetic resonance, and pyridine adsorption-infrared spectroscopy, and its performance of removing trace amount of olefins from mixed aromatics was investigated in a bench-scale continuous-flow fixed bed reactor. The results showed that the pore structure and acidity of the USY molecular sieve could be effectively adjusted by ammonium fluoride modification; the framework aluminum component was extracted and deposited in the pores, the micro pore volume was basically unchanged; the pore size decreased, but the mesoporous and large pore volumes increased. The Lewis acid content of modified molecular sieve was 3 times that of before modification, but the change of Bronsted acid content was small. It is proved that the F-modified USY sieve can greatly reduced catalyst deactivation and increase the conversion rate of olfines.

Key words: USY molececular sieve, ammonium fluoride modification, acid site, deolefination