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A polymerization catalyst is prepared by a process which includes the step of treating silica-supported chromium oxide with a permanganate compound such as potassium permanganate. The catalyst is then activated such as by sequential heating in a reducing atmosphere and an oxidizing atmosphere. The c

A polymerization catalyst is prepared by a process which includes the step of treating silica-supported chromium oxide with a permanganate compound such as potassium permanganate. The catalyst is then activated such as by sequential heating in a reducing atmosphere and an oxidizing atmosphere. The catalyst can be used in particle-form polymerization to produce ethylene polymers having lowered shear response for a given melt index.

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1. A method for preparing a polymerization catalyst comprising the steps of (a) contacting a material comprising silica-supported chromium oxide or a compound oxidizable to chromium oxide with a solution of a permanganate compound; (b) heating the thus-contacted material in a reducing atmosphere

1. A method for preparing a polymerization catalyst comprising the steps of (a) contacting a material comprising silica-supported chromium oxide or a compound oxidizable to chromium oxide with a solution of a permanganate compound; (b) heating the thus-contacted material in a reducing atmosphere at a temperature in the range of about 600° C. to about 1100° C.; and then (c) heating the material in an oxygen-containing atmosphere at a temperature in the range of about 450° C. to about 1000° C. for at least about one-half hour. 2. The method of claim 1 in which the permanganate is potassium permanganate. 3. The method of claim 2 in which the catalyst contains chromium in an amount of about 0.001 to about 10 weight percent based on the weight of the catalyst. 4. The method of claim 3 in which the catalyst contains titanium in an amount within the range of about 0.5 to about 10 weight percent based on the weight of the catalyst. 5. The method of claim 4 in which the temperature of step (b) is in the range of about 760° C. to about 925° C. 6. The method of claim 5 in which the temperature of step (c) is in the range of about 650° C. to about 870° C. 7. The method of claim 6 in which the potassium permanganate is employed in the form of a solution of potassium permanganate in acetonitrile. 8. The method of claim 6 in which the chromium is present in an amount of from about 0.1 to 5 weight percent. 9. The method of claim 8 in which the reducing atmosphere comprises carbon monoxide. 10. The method of claim 9 in which the reducing atmosphere comprises a mixture of carbon monoxide and nitrogen. 11. The method of claim 9 in which step (c) is carried out in an atmosphere comprising air. 12. The method of claim 11 in which the contacted material is chromium oxide supported on a silica-titania cogel which has been calcined in air. 13. The method of claim 12 in which steps (b) and (c) are carried out under fluidized bed conditions. 14. The method of claim 1 in which the contacted material is prepared by admixing sodium silicate and sulfuric acid containing titanyl sulfate to form a gel, impregnating the gel with aqueous chromium oxide, azeotrope drying the gel, and calcining the gel in air. 15. A polymerization catalyst prepared by the process of claim 1, 2, 3, 4, or 12. 16. The method of claim 1 in which the chromium oxide or compound oxidizable to chromium oxide is supported on a silica-titania support and the permanganate compound is in a non-aqueous solution. 17. The method of claim 16 in which steps (b) and (c) take place under fluidized bed conditions. 18. The method of claim 17 in which the reducing atmosphere comprises carbon monoxide.