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

• Main Author: Mattos,Flávia C. G. de
• Publication Date: 2017
• Other Authors: Carvalho,Eduardo N. C. B. de, Freitas,Elon F. de, Paiva,Mateus F., Ghesti,Grace F., Macedo,Julio L. de, Dias,Sílvia C. L., Dias,José A.
• Format: Article
• Language: eng
• Source: Journal of the Brazilian Chemical Society (Online)
• Download full: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000200336
• topic: supported heteropolyacid; 12-tungstophosphoric acid; silica-alumina; ethanol; esterification of acetic acid with ethanol

This work deals with preparation and characterization of H3PW12O40 (H3PW) supported on silica-alumina. Impregnation of H3PW (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.% H3PW/SiO2-Al2O3 had the highest activity under the conditions: catalyst calcination at 300 ºC, temperature of 100 ºC, 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 ºC).