Synthesis of Amorphous Silica–Alumina Materials with Obviously Enhanced Brønsted Acidity by High-Gravity Technology for Plastic Degradation

Amorphous silica–alumina (ASA) is widely used in chemical industries due to its unique structure and Brønsted acidity. In this study, mesoporous ASA with obviously enhanced Brønsted acidity was synthesized by high-gravity technology. With the increase of Si/Al ratio, the fraction of tetra-coordinated aluminum (AlIV) in the ASA precursors and the concentration of Brønsted acid sites (CBAS) of ASA gradually increased. It was also found that the high-gravity technology could increase CBAS by over 76% compared to the conventional stirred tank reactor at the same Si/Al ratio. This enhanced Brønsted acidity is primarily due to the powerful mixing effect of the rotating packed bed reactor, which facilitates the formation of Si–O–Al bonds and AlIV through a more uniform distribution of silicon and aluminum. Finally, the relationship between the acidity of ASA and its catalytic activity for plastic degradation was investigated. ASA was found to significantly reduce the degradation temperature of polyethylene, polypropylene, and polycarbonate. The polyethylene degradation experiment also showed that increasing the CBAS can effectively improve the pyrolysis activity. This high-performance ASA prepared by a high-gravity technology is expected to be used in catalysts for petrochemical and environmental protection applications.