Disclosed are catalyst systems and methods of making the catalyst systems for the polymerization of an olefin containing a solid titanium catalyst component containing an inorganic titanium compound, a magnesium alcohol adduct made from an inorganic magnesium compound and an alcohol, and a porous support having at least one of a certain specific surface area, a certain pore volume, and a certain median particle size. The catalyst system may further contain an organoaluminum compound and optionally an organosilicon compound. Also disclosed are methods of making polyolefins.