Effects of Al Distribution on Phosphorus Modification and Catalytic Cracking Performance of FER zeolites

Abstract The effects of aluminum (Al) distribution in FER zeolites on phosphorus modification and catalytic cracking performance are systematically investigated in this work. To achieve this purpose, FER zeolites with distinct Al distributions were synthesized with three OSDAs: pyrrolidine (Pyrr), n-butylamine (NBA), and pyridine (Py). According to one-dimensional (1D) 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) experiments, it is elucidated that the framework Al atoms at T3 sites of FER zeolites are susceptible to removal during thermal treatment, hydrothermal aging, phosphorus modification, and subsequent hydrothermal aging. Also, combined with 1D 29Si and 2D 27Al 3Q MAS NMR spectra, the stability differences of FER zeolites during the aforementioned post-treatments were further clarified: FER(NBA) zeolites possess moderate stability, while FER(Pyrr) and FER(Py) zeolites exhibit the poorest and highest stability, respectively. Notably, benefiting from their moderate stability, FER(NBA) zeolites avoided excessive dealumination and deficient P–Al interaction during phosphorus modification and subsequent hydrothermal aging, further generating abundant Si–OH–Al–O–P active sites for catalytic cracking, which contributed to the highest conversion and light olefin yield in 1-octene cracking.