Preparation and activity of the catalysts for the synthesis of carboxylic ester with high boiling point

A series of rare earth sulfates catalysts were prepared by hot- impregnation method from rare earth oxides and sulfuric acid, followed by calcination and activation at 470-500°C. Using the synthesis of dibutyl phthalate as test reaction, the catalytic activities of samples were examined in detail, especially about the activities of ceric sulfate containing hydrate water and its composite with transition metal sulfates. The results indicated that Ce(SO₄)₂ · xH₂O (x = 4) exhibited considerably high activity. Catalyzed by ceric sulfates prepared and at the optimal reaction conditions, the conversion of carboxylic acid with high boiling point (b.p.) were 77.1%, which was remarkably higher than that catalyzed by sulfuric acid. Moreover, the reaction could be carried out at relatively lower temperature. Meanwhile, taking into account the orbital structure of sufficient energy- level of rare earth ions and based on Bronsted's acid-base theory, the catalytic activity results of Ce(SO₄)₂ · 4H₂O were analyzed in detail. Also, the surface acidity properties of various samples were characterized by the adsorption of pyridine as probe molecule studied by IR spectroscopy.