One-step synthesis of chromium and aluminium containing SBA-15 materials: New phillips catalysts for ethylene polymerization

New CrAlSBA-15 mesoporous materials have been prepared by direct synthesis and characterized by ICP-AES, XRD, N2 adsorption, 27Al NMR, TEM, UV–vis and H2-TPR. CrAlSBA-15 materials exhibited high mesostructural order starting from chromium(III) nitrate (Si/Cr = 66; Si/Al = 35 at pH 3) and from chromium(III) acetate hydroxide (Si/Cr = 39; Si/Al = 51 at pH 1.5). The incorporation of chromium and aluminium into SBA-15 mesoporous structure is enhanced by increasing the pH and produces an increase in pore size and pore volume. After calcination, samples prepared by one-step synthesis showed Cr(VI) centres well dispersed with a proportion of chromate species higher than Cr/AlSBA-15 catalysts prepared by impregnation and grafting. H2-TPR measurements showed that only the 80% of Cr(VI) ions incorporated into the SBA-15 structure were reduced, so part of chromium ions may be located in non-accessible positions inside the solid walls.CrAlSBA-15 materials obtained by direct synthesis exhibited higher ethylene polymerization activity (381.1 kg PE/g Cr h) than Cr/AlSBA-15 and conventional Cr/SiO2 Phillips catalyst prepared by impregnation (260.5 and 216 kg PE/g Cr h, respectively).