Supported Chromium Oxide Catalysts for Olefin Polymerization. VI. Activation Process and Catalytic Activity Versus Ethylene Polymerization

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Abstract
The influence of the temperature, time, and heating rate of the activation process of a chromium oxide catalyst, supported on silica-alumina, on the activity vs. ethylene polymerization has been studied. The function of the activation process is to develop the potential active sites through a rapid interaction between the chromium oxide and the support which depends only on the temperature, and also to cause a minimum time- and temperature-dependent dehydration of the solid. Pretreatments by limited amounts of hydrogen, ethylene, or other hydrocarbons lead to an increase of the activity through optimal conditions; the optimal activity results from a compromise between a proper reduction of the chromium and the desorption of the oxidized products. The better pretreat-ment agent is the monomer itself in limited amount at high temperature.