Study on Nickel Oxide-Silica-Alumina Catalyst for Ethylene Polymerization. I. Catalyst Activity for Ethylene Polymerization and Selectivity in the Formation of Butene-Isomers

The activity for the ethylene polymerization per unit mass of the catalyst has been found highest for the catalyst with the Al/(Al+Si) ratio of 0.05. The high activity is ascribed to the high specific activity per unit surface area as well as to the large specific surface area of the catalyst. The pore sizes scarcely produce any effect on the catalyst activity. Even at a very short reaction time, the three isomers of n-butene are produced simultaneously. The ratios both of cis- and of trans-2-butene to 1-butene increase with the reaction time more or less according to the aluminum content, whereas for all the catalysts the ratio between the two 2-butene isomers is kept at values approximate to 1. At the zero extent of reaction, the former ratios, given as a function of the aluminum content, show an increase with the progressively increasing content up to the highest value at the Al/(Al+Si) ratio of 0.1, while the latter remains nearly constant throughout all the catalysts. For the sake of a convenient explanation of the change in the selectivity as well as in the activity related to the aluminum content of the present catalysts, two kinds of acid sites are suggested as possibly present.