Catalytic performances of heteropoly compounds supported on dealuminated ultra-stable Y zeolite for liquid-phase esterification

A series of catalysts of 12-Phosphotungstic acid (PW) and its cesium salts immobilized on dealuminated ultra-stable Y zeolite (DUSY) were prepared. Their specific surface area and acid strength were characterized, and their catalytic activity, selectivity and stability were evaluated in the liquid-phase esterification of acetic acid with n-butanol. It was found that the catalytic activity could be improved remarkably by introducing PW onto dealuminated USY (from 49.5% to 86.4%). However, this obvious promotion effect of PW could not be observed on USY supported PW catalyst, which showed rather low conversion of less than 25.0%. The supported cesium salt of PW on DUSY catalyst gave a very high conversion of n-butanol of 94.6% and the 100% selectivity for n-butyl acetate. The catalytic stability test revealed that after 5 reaction cycles, the catalytic activity over PW/DUSY drastically dropped to 47.6%, by contrast, the PW cesium salt/DUSY still showed a high conversion of 81.6%. The leaching test for catalysts in water showed that the decrease of activity was closely associated with the solubility of the active heteropoly components on supports into the polar solvent, which indicates that the catalytic deactivation was mainly due to the lose of the heteropoly species in the reaction medium. The high catalytic stability of the supported cesium salts of PW is suggested to be derived from the water-tolerance of cesium salts of PW in the polar reaction system.