Abstract: Amorphous silica-alumina (ASA) is characterized by moderate acidity and large pore sizes, and is commonly used in catalysts for processes such as hydrocracking and catalytic cracking. In this study, ASA with varying SiO₂ compositions was prepared using the pH-swing method. The physicochemical properties of the samples were characterized using techniques such as TEM, XRD, N₂ adsorption-desorption, pyridine adsorption-IR spectroscopy, and solid-state NMR.The results indicate that as the SiO₂ mass fraction increased from 9.4% to 39.1%, the specific surface area of ASA decreased from 443 m²/g to 367 m²/g, the proportion of tetra-coordinated aluminum increased from 29.2% to 42.0%, and the content of Bronsted acid sites (at a desorption temperature of 200°C) increased from 7.8 μmol/g to 34.8 μmol/g. Further hydrothermal treatment of the samples revealed that as the hydrothermal temperature increased, the specific surface area of ASA gradually decreased, while the Bronsted acid number gradually increased. When the prepared ASA was used in the pyrolysis reaction of PE plastic, a higher Bronsted acid number of ASA resulted in a lower plastic pyrolysis temperature and higher cracking activity.

Key words: amorphous silica-alumina, pH-swing method, hydrothermal treatment, pore structure, acidity, plastic pyrolysis