Highly active catalysts for olefin polymerization and a polymerization process using these catalysts

Highly active catalyst comprising the reaction product of:

• a) tetraneophylzirconium with
• b) metal oxides selected from the group consisting of IIa, IIIa, IVa and IVb metal oxides having a partly hydroxylated surface, or mixtures thereof,
• in a hydrocarbon as the reaction medium, the resulting catalyst optionally being hydrogenated, wherein the resulting catalyst contains the by-products formed during the reaction in an amount not exceeding 1.1% by weight, said by-products comprising tert-butylbenzene.