Abstract: This invention relates to a process for the manufacture of olefin polymers by polymerization of monoolefins with the aid of a silicic xerogel/chromium trioxide catalyst obtained by (1) synthesizing a particulate silicic xerogel, (2) doping this xerogel with chromium trioxide or a chromium compound which converts to chromium trioxide under conditions of stage (3) and (3) maintaining the resulting product at an elevated temperature in a water-free oxygen-containing stream of gas. The characteristic feature of the process of the invention is that the silicic xerogel/chromium trioxide catalyst used is one obtained by (1) synthesizing the silicic xerogel in the first stage as follows: (1.1) taking an aqueous solution of a sodium silicate, (1.2) substituting substantially all of the sodium ions contained in said solution by hydrogen ions by means of an ion exchanger, (1.3) introducing a water-soluble aluminum salt into the resulting aqueous silicic acid solution, (1.

Abstract: A process for the manufacture of olefin polymers by polymerization of .alpha.-monoolefins by means of a silicic acid xerogel/chromium trioxide catalyst, which is obtained by a method wherein (1) a finely divided silicic acid xerogel is first manufactured by (1.1) employing a silicic acid hydrogel of relatively high solids content, (1.2) extracting at least 60% of the water contained in the hydrogel from the latter by means of a particular organic liquid, (1.3) drying the gel thus obtained until there is no further loss in weight (xerogel formation) and (1.4) reducing the xerogel thus obtained to particles of diameter from 20 to 2,000 .mu.m,2. this xerogel is then charged with the desired amount of chromium from a solution of chromium trioxide or a solution of a chromium compound which under the conditions of stage (3) is converted to chromium trioxide, with evaporation of the solvent, and3. finally the product thus obtained is heated in an anhydrous stream of gas containing oxygen.