Cracking of n-Butane Over Alkaline Earth-Containing HZSM-5 Catalysts

A series of catalysts, NiSO₄/SiO₂–Al₂O₃, for ethylene dimerization were prepared by the impregnation method using aqueous solution of nickel sulfate. Although SiO₂–Al₂O₃ without NiSO₄ was inactive as catalyst for ethylene dimerization, the SiO₂–Al₂O₃ with NiSO₄ exhibited high catalytic activity even at room temperature. The high catalytic activity of NiSO₄/SiO₂–Al₂O₃ was closely correlated with the increase of acidity and acid strength due to the addition of NiSO₄. The sample having 15 wt% of NiSO₄ and calcined at 500 °C for 1.5 h exhibited maxima for catalytic activity and acidity. In view of IR results of CO adsorbed on NiSO₄/SiO₂–Al₂O₃, it is concluded that the active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni⁺, and an acid.