Hydrothermal Synthesis of AlV‐Rich Nonporous Amorphous Silica‐Alumina for Stable Cracking of Plastics Waste into Light Olefins

Abstract Fast coking and limited selectivity toward light olefins are two drawbacks of the zeolitic upcycling of polyolefin‐based plastic waste. The Al V –rich amorphous silica‐alumina (ASA) catalysts with the strong Brønsted acidic sites (BAS) might be an alternative to the zeolites; however, the existing preparations are costly and complex. A hydrothermal preparation of Al V ‐rich (37.90–43.46%) nonporous ASA catalysts is presented, which is achieved by collecting the synthesis gel of an FAU‐type structure during its induction period. The resultant ASA catalysts demonstrated (very) strong BAS, depending on the Al V /Al IV ratio, and a high density of Lewis acidic sites (LAS), which are stronger than the industrially relevant zeolites. The ASA catalysts examined in the cracking of various polyolefin‐based plastics resulted in excellent polymer degradation activity, increased light olefins production, high‐quality heavy aromatics‐free liquid oils, and up to zilch coking, which are clearly superior to those obtained using a crystalline zeolite. Despite having (very) strong BAS, the exceptional light olefins production and suppressed coke formation by the ASA catalysts are possibly due to the synergy between a high density of LAS and free mass transfer, which favors the monomolecular over the bimolecular cracking mechanism.