Characterization of SO₄^2-/TiO₂ - Al₂O₃ solid acid catalyst and its catalytic activity in tetraoctyl pyromelliate (terra-2-ethylhexyl pyromellitate) synthesis

A series of sulphated Al₂O₃-TiO₂ mixed oxides were prepared and used as catalysts in synthesis of tetraoctyl pyro-mellitate. The catalysts were characterized by means of XRD, NH₃ - TPD, TG, IR, BET and EDS methods. From XRD pattern it was found that crystallization of TiO₂ was inhibited with addition of Al and kept smaller sizes crystals. As a result, the specific surface area of SO₄^2-/TiO₂-AlO₂ catalyst was larger than SO₄^2-/TiO₂. The sample containing Al contained more sulphur than samples without Al which indicated Al could stabilize S on catalyst surface and reduced its loss at high calcinations temperature. Both the strength and acid amount increased with the addition of 23.1% (mole fraction) Al. The catalyst containing 23.1% Al (mole fraction) and being calcined at 400°C showed best catalytic activity. The conversion of the pyromellitic dianhydride was up to 98.2% after 2 h reaction.