A shaped catalyst body for the oxidation of SO2 to SO3, which comprises vanadium, at least one alkali metal and sulfate on a silicon dioxide support material, wherein the shaped body has the shape of a cylinder having 4 hollow-cylindrical convexities, obtainable by extrusion of a catalyst precursor composition comprising vanadium, at least one alkali metal and sulfate on a silicon dioxide support material through the opening of an extrusion tool, wherein the opening of the extrusion tool has a cross section formed by 4 partly overlapping rings whose midpoints lie essentially on a circular line having a diameter of y, wherein the rings are bounded by an outer circle having an external diameter x1 and an inner circle having an internal diameter x2.