The invention relates to a process for preparing a catalyst for the polymerization
of olefins, which comprises:
- a) preparation of a finely divided silica xerogel,
- b) loading of the xerogel with chromium from a solution of chromium
trioxide or a chromium compound which is converted into chromium trioxide under
the conditions of step c), and
- c) activation of the resulting product at from 400 to 1100 C.
in a water-free gas stream comprising oxygen in a concentration of above 10% by volume,
wherein a fluoride doping with a fluorinating agent is carried out in step
b) or in step c). Furthermore, the invention relates to a catalyst for the polymerization
of olefins which is obtainable by the process of the invention and to a process
for the polymerization of olefins in which an olefin or an olefin mixture is polymerized
in the presence of a catalyst according to the invention.
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