Reivindicaciones

1. Process for the polymerization of ethylene wherein ethylene and an ∀-olefin are polymerized in the presence of a catalyst system comprising a chromium-containing catalyst supported on silica, a titanium-containing catalyst supported on silica and a cocatalyst for the activation of the titanium-containing catalyst. 2. Process according to claim 1 wherein the chromium containing catalyst and the titanium containing catalyst are introduced into the olefin polymerisation reactor through individual dosing 3. Process according to claim 1 wherein the chromium containing catalyst and the titanium containing catalyst are pre-mixed for joint addition into the olefin polymerisation reactor. 4. Process according to claims 1-3 wherein the concentration of chromium in the chromium containing catalyst is from 0.1 to 5% by weight. 5. Process according to claims 1-4 wherein the comonomer is selected from: propene, 1-butene, 1-pentene, 1-hexene, 1-methyl-4-pentene, 1-octene, 1-decene. 6. Process according to claims 1-5 wherein the cocatalyst is selected from triethylaluminum and isobutylaluminum. 7. Process according to claims 1-6 wherein the chromium-containing catalyst and the titanium-containing catalyst are used in a weight ratio from 95:5 to 5:95. 8. Polyethylene obtainable by the process of claims 1-7.