Study on the Interaction Between Ni2+ and SO42− on the Surface of ZSM-5 Catalyst and the Effect on n-Butene Oligomerization

The identification of key active sites that determine oligomerization degree is a key focus of research in olefin oligomerization. The Ni/S-HZSM-5 catalyst has attracted widespread attention due to its excellent performance in this reaction. However, the interaction between SO42− and Ni2+ on the ZSM-5 support, especially quantitatively regulating their ratio, has been rarely investigated. In this study, we prepared a series of Ni/S-HZSM-5-x catalysts by fixing the Ni loading and varying the Ni/S molar ratio in the initial feedstock. Then, the obtained catalysts were characterized to systematically investigate how the Ni/S ratio affects their structure, properties, and n-butene oligomerization performance. The results indicate that tuning the Ni/S ratio enables the targeted regulation of surface acidity and electronic properties of the catalysts. The Ni/S ratio influenced the interaction between the Ni cation and SO42−-SO32− complex, which in turn altered the Lewis acidity of the catalysts. Further evaluation results reveal that n-butene conversion is positively correlated with the catalyst’s acidity, and the Ni2+/Ni+ ratio is positively correlated with the carbon chain length of the products. The surface form of NiSO4 is the primary factor determining Lewis acidity, which is directly associated with the chain-growth ability of the catalyst.