Ziegler catalysts

Claim 1

In a Ziegler catalytic system formed by the combination of an organo-metallic compound of a metal of Group I, II or III of the Periodic System of the Elements according to Mendeleef and a compound of a heavy metal of Group IV, V or Vi of said Periodic System supported on an alumina carrier, the improvement wherein the carrier is essentially an activated amorphous alumina containing from 0.3 to 30% by weight of one or more salts of aluminum with at least one oxygenated inorganic anion selected from the group consisting of sulphate, phosphate, chlorate, perchlorate and halogen-sulphonate anions or of a mixture of the latter with one or more salts of aluminum with halogen anions, said activated amorphous alumina being prepared by precipitating aluminum hydroxide gel from a solution of aluminum salt at a pH value of from 7 to 10, introducing said inorganic anions into said gel by co-precipitation with and/or further addition to the latter, in such conditions as to ensure in the alumina content of inorganic anions of from 0.2 to 25% by weight and a content of cations other than aluminum of less than 0.25% by weight, the permanence time of the gel under moist conditions being less than 12 hours, drying the gel and activating the resulting amorphous alumina by calcination at a temperature of from 250° to 700° C.