Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

This work deals with preparation and characterization of H 3 PW 12 O 40 (H 3 PW) supported on silica-alumina.Impregnation of H 3 PW (15, 20, 30 and 40 wt.%) on commercial silica-alumina support in acidic aqueous solution is effective for preparing this catalyst keeping its Keggin structure, according to different methods of characterization.The catalysts were tested in a model reaction of acetic acid with ethanol and 30 wt.% H 3 PW/SiO 2 -Al 2 O 3 had the highest activity under the conditions: catalyst calcination at 300 °C, temperature of 100 °C, acetic acid:ethanol molar ratio of 2:1 and catalyst:acetic acid mass ratio of 10 wt.%.The reaction yield was 79 and 100% selectivity for ethyl acetate over three reutilizations, for reaction time of 2 h.The calculated total acid site distribution was 0.299 mmol g -1 (97% of the theoretical probed by pyridine), and most of these (0.236 mmol g -1 ) were Brønsted weak-medium strength (pyridine desorption between 300 and 500 °C).