Abstract: Olefin polymerisation catalyst on a porous inorganic support comprising (i) 99.5 to 83.3 parts by weight of SiO.sub.2, (ii) 0.5 to 10 parts by weight of Titanium and 0.85 to 1.15 parts by weight of chromium, this catalyst having a pore volume of 0.9 to 1.15 cc/g, a surface area of 440 to 540 m.sup.2 /g and a mean pore diameter of between 70 and 100 Angstroms.

Abstract: Microspherical cogel particles comprising silica and at least one other metal oxide are prepared by forming a slurry of porous particulate material comprising silica and a liquid medium comprising at least 90%, by weight of the liquid medium, of an organic liquid and subjecting the slurry to spray drying. The method enables agglomeration of particulate material of especially small particle size to obtain microspherical particles of a size especially suitable for us as a catalyst support. The particles have a pore size of at least 2 cc/g and, especially when the particles contain titanium atoms, are especially suitable for use in the preparation of a catalyst for the polymerization of olefins.