The Preparation of Solid Superacids SO_4~(2-)/Fe_2O_3 and Their Catalytic Activity in Esterification

The solid superacid SO 2- 4/Fe 2O 3 was prepared by calcining FeSO 4·7H 2O directly and the influence of calcining temperature, calcining time to its catalytic activity in esterification was investigated. The data of the catalysts (such as mole ratio of SO 2- 4 and Fe 2O 3 and surface acidity etc) were obtained. The optimal condition in preparation of solid superacid SO 2- 4/Fe 2O 3 is: calcining temperature 550 ℃, calcining time 5 h. Under this condition the mole ratio of SO 2- 4 and Fe 2O 3 in the obtained solid superacid SO 2- 4/Fe 2O 3 was 1.71 and the corresponding acid concentration on its surface was maximal (3.47 mmol/g) so that its catalytic activity in esterification was the best. When the acid concentration on the catalyst surface was higher or lower than this value, its catalytic activity in esterification was decreased. When the catalyst absorbed suitable amount of water, its acid concentration on the catalyst surface and catalytic activity in esterification was increased too. On the other hand, if the catalyst absorbed much more water, its catalytic activity in esterification would be lost.