Acid catalyzed organic transformations by heteropoly tungstophosphoric acid supported on MCM-41

In this work, solid acid catalysts of the Keggin-type 12-tungstophosphoric acid (H3PW12O40, HPW) incorporated within the mesochannels of MCM-41 are prepared through a simple and effective impregnation method. The catalysts are characterized by various techniques such as XRD. FTIR, TEM, N-2 adsorption and thermal analysis. The surface acidities are measured by non-aqueous titration of n-butyl amine in acetonitrile and FTIR spectra of chemisorbed pyridine. The acidity and the textural parameters of the nanocomposites can be controlled simply by changing the loading of HPW on the MCM-41. The results indicate that the surface saturation coverage of MCM-41 is reached with 60 wt% HPW. The high saturation coverage is indicative of the well-dispersion of HPW within the mesochannels of MCM-41. The catalytic activities of the HPW/MCM-41 catalysts for the Pechmann, esterification reaction and Friedel-Crafts acylation reactions are studied in detail. Both the surface acidity and the catalytic activity sharply increase with the modification of MCM-41 by HPW. The sample with 60 wt% HPW shows the highest acidity and catalytic activity. The reusability tests of the catalysts show that the catalysts can be used several times without significant loss in activity. The HPW/MCM-41 catalysts have great potential for applications as commercial catalysts in promoting acid-catalyzed organic transformations under environmental friendly conditions and processes. (C) 2011 Elsevier B.V. All rights reserved.