Quantitative Relationship Between Activity and Acid Site Distribution in the Oligomerization of Ethylene Over MCM-41 Catalyst

Abstract

Nickel ion exchanged MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41 were prepared and used to catalyze ethylene oligomerization which was performed in a fixed bed model (T = 523 K, P = 2 MPa). A temperature programmed desorption of ammonia (NH3-TPD) method was employed to quantitatively determine the acid strength distribution of Ni-MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41. The TPD spectrum was analyzed by an interrupted-TPD method with desorption-control (dc-method) to obtain the desorption activation energy of ammonia, which can be used as acid strength scale for the purpose of correlation with catalytic activity. A quantitative relationship between catalyst acidity and catalytic activity was established by a Bronsted type equation. The site with desorption activation energy of ammonia E = 124 kJ mol−1 was found as the most suitable site for ethylene oligomerization. An approximate linear relationship is obtained between the activity of the ethylene oligomerization reaction and the acid amount corresponding to the acid site with E = 124 kJ mol−1.