铈含量对CeUSY分子筛抗镍性能的影响及机理研究

采用液相离子交换法制备了不同Ce含量的CeUSY分子筛，并通过Mitchell等体积浸渍法对其进行Ni污染，运用ICP-AES、XRD和N₂吸附等温线等方法对其织构性质进行表征，并利用微反应活性评价装置考察了其抗镍性能。结果表明，不同Ce含量改性的USY样品其抗镍效果存在差异，CeUSY分子筛的抗镍效果与Ce含量的关系呈现火山型变化。结合Ni污染前后CeUSY分子筛的H₂-TPR和Py-FTIR表征结果探讨了Ce物种的抗镍机制，证实了Ce物种形态的变化是不同Ce含量的CeUSY分子筛具有不同抗镍效果的重要成因，其中，SOD笼中的Ce（OH）²⁺在高温条件下可与Ni（OH）⁺相互作用，脱去一分子H₂O形成Ce³⁺-O-Ni²⁺的稳定结构，阻碍了Ni物种与骨架铝的结合导致CeUSY分子筛中B酸中心的破坏，同时有效抑制了易还原NiO物种的生成。而Ce含量过高使得SOD笼内的Ce物种变成二聚以及三聚物，与Ni（OH）⁺作用减弱，使其抗镍性能减弱。

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.