2.4. CharacterizationElemental analysis of the catalysts was carried out by first treat-ing them with H2SO4(7.2 M) solution. Ti contents were determinedby a spectrophotometric method with H2O2at 410 nm, while Zrcontents were obtained by the same method with arsenzo III at666 nm.Al contents were determined by titration with EDTA. Inter-nal electron donor contents were acquired by gas chromatographyafter the organic compounds had been extracted into heptane.The X-Ray diffraction (XRD) patterns of catalysts were recordedin the X-ray diffractometer DMAX-2400 using Cu K radiation( = 1.5406˚A) at a generator voltage of 40 kV and generator currentof 40 mA. Scanning range was 2 = 3–80oat a rate of 2◦min−1.Catalysts textural properties were determined by nitrogenadsorption–desorption isotherms at 77 K with an ASAP2020Quantachrome equipment. Surface areas were calculated with BETequation whereas pore size distributions and average pore sizewere determined by BJH method applied to the adsorption branch