Engineering of sulfate ions migration in Fe2O3-doped NiSO4/Al2O3 catalysts to enhance the selective trimerization of propylene

Abstract

Propylene, a readily accessible and economically viable light olefin, has garnered substantial interest for its potential conversion into valuable higher olefins through oligomerization processes. The distribution of products is profoundly influenced by the catalyst structure. In this study, Fe₂O₃-doped NiSO₄/Al₂O₃ catalysts have been meticulously developed to facilitate the selective trimerization of propylene under mild conditions. Significantly, the 0.25Fe₂O₃-NiSO₄/Al₂O₃ catalyst demonstrates an enhanced reaction rate (48.5 mmol_C3/(g_cat.·h)), alongside a high yield of C9 (~ 32.2%), significantly surpassing the performance of the NiSO₄/Al₂O₃ catalyst (C9: ~24.1%). The incorporation of Fe₂O₃ modifies the migration process of sulfate ions, altering the Lewis acidity of the electron-deficient Ni and Fe sites on the catalyst and resulting a shift in product distribution from a Schulz-Flory distribution to a Poisson distribution. This shift is primarily ascribed to the heightened energy barrier for the β-H elimination reaction in the C6 alkyl intermediates on the doped catalyst, further promoting polymerization to yield a greater quantity of Type II C9. Furthermore, the validation of the Cossee-Arlman mechanism within the reaction pathway has been confirmed. It is noteworthy that the 0.25Fe₂O₃-NiSO₄/Al₂O₃ catalyst exhibits remarkable stability exceeding 80 h in the selective trimerization of propylene. These research findings significantly enhance our understanding of the mechanisms underlying olefin oligomerization reactions and provide invaluable insights for the development of more effective catalysts.