The Chromium catalysts supported on silica for ethylene polymerization were prepared by mixing, impregnation, and coprecipitation methods and their caralytic activities were examined. As a consequence, it was found that both of co-precipitated and impregnated catalysts were very active, but mixed catalyst exhibited little catalytic activity. Co-precipitated and impregnated catalysts showed maximum polymerization activity under evacuation at 600 ℃ for 1 hr.
The active site responsible for ethylene polymerization was proved to be Cr³⁺ ion, as evidenced by the relationship between variation of catalytic activity and CO reduction time, the color change in reduced catalyst, and the infrared spectra of adsorbed nitric oxide. The catalyst was poisoned with sodium ion and its activity decreased with increase in the amount of sodium ion until 20 ppm.