the invention relates to supports comprising inorganic oxide nanoparticles coated with magnesium chloride and a method for making them . the inorganic oxide has a mean particle diameter of less than 5 microns and is used as a seed to crystallize magnesium chloride from solution . the magnesium chloride - coated inorganic oxide is useful for supporting transition metal compounds ; the supported transition metal compounds are used as catalysts for polymerizing olefins .