Recycling of Spent FCC Catalysts: Conversion of Leached Residues to Zeolite ZSM‐5

Abstract The commercial recycling of spent FCC catalyst typically focuses on recovering only 1–3 % of rare‐earth elements, with the remaining residues often disposed of in landfills. Here, we present a novel method to close a recycling loop for spent FCC catalyst. The method involves a series of leaching steps: Firstly, the spent catalyst material is leached with HNO 3 to remove rare‐earth elements such as La; second, solvothermal leaching with HCl removes most of Al and impurities like Fe, Ni and V; finally, a third leaching with H 2 SO 4 removes Ti. The solid residues are then used to synthesize ZSM‐5 without the addition of any extra silicon or aluminum sources after mild activation. The impurities in the synthesis gel strongly modify the properties of the zeolite, with ZSM‐5 crystals containing higher levels of impurities exhibiting lower crystallinities, surface areas, acidities, cracking activities, as well as larger particle sizes.