| 摘要 |
<p>High melt flow olefin polymers suitable for such applications as injection molding, and the like requiring a narrow molecular weight distribution are produced using a catalyst made by reducing and reoxidizing a chromium catalyst on either a titaniumsilica cogel or a self-reduced silica-containing composition. In the first embodiment, a cogel formed by coprecipitating silica and titania, and containing a chromium compound, is treated in a non-oxidizing atmosphere, such as CO, hydrogen, N2 or a material decomposable to these materials, and thereafter reoxidized. In the second embodiment, a titanium-free chromium-containing catalyst is first heated in air or the like to dry the catalyst and oxidize the chromium after which it is heated in an inert atmosphere wherein the composition is self-reduced to give chromium in a lower valence state. The resulting selfreduced composition is then heated in a reducing ambient and then reoxidized as in the first embodiment.</p> |
