Study of Nickel Oxide-Silica-Alumina Catalysts for Ethylene Polymerization. III. The Performance of the Catalysts in Ethylene Polymerization and Butene Isomer Formation and Its Dependence on the Nickel Oxide Content

Abstract

Abstract The activity of nickel oxide-silica-alumina catalysts in ethylene , polymerization and the selectivity in the formation of three n-butene isomers as the primary products have been studied by employing a series of catalysts with identical aluminum contents but different nickel contents. Also studied have been the changes brought about by nickel removal in the catalyst acidity and in the specific surface area. In the series of catalysts studied, the specific activity, i. e., the activity per unit surface area of the catalyst, increases with the increasing nickel content of the catalyst, attaining a maximum at 3 atm.% nickel. When the specific activity is plotted against the difference between the specific acidity values observed before and after the removal of nickel, the plot falls approximately on the straight line obtained with a series of catalysts which are the same in nickel content but different in aluminum content. On the other hand, for all the catalysts used in the present and previous studies, the selectivity is more closely related to the Al/Ni ratio than to either aluminum content or nickel content. Two kinds of active sites have been presented in order to explain the present observations. One kind of active site is the nickel acid site, which contributes to the polymerization of ethylene while facilitating the isomerization to some extent. The other site is the aluminum acid site in contact with the former; it contributes to the initial-bond shift.