Mechanism and effects of cerium content on the nickel olerance of CeUSY zeolite

The CeUSY zeolites loaded with Ce were prepared by liquid phase ion exchange method, and the Ni contamination was conducted by Mitchell impregnation method. The texture properties were characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and N₂ adsorption. Moreover, the nickel tolerance was evaluated by the MAT evaluation device. The results show that CeUSY zeolites with different Ce contents possess a nickel tolerance performance varying in a volcano type with the increase of Ce content. Through the H₂-TPR and Py-FTIR characterization of CeUSY zeolite before and after Ni contamination, it is evident that the change in Ce species morphology is one of the reasons affecting nickel tolerances. It is thought that the interaction between Ce(OH)²⁺ and Ni(OH)⁺ in the SOD cages of the CeUSY zeolite results in a loss of H₂O molecule to form a stable Ce³⁺-O-Ni²⁺ structure at high temperature, which hinders the combination of Ni species with the framework aluminum to prevent the destruction of the Brønsted acid sites in CeUSY zeolite and effectively inhibits the formation of reducible NiO species. However, with the increase of the content of Ce³⁺, the part of the introduced Ce would happen to self-assemble in the zeolites as multinuclear hydroxylated species which interacts weakly with Ni²⁺ species compared to mononuclear species and then reduces the nickel tolerance.