Effect of microwaves in the dealumination of mordenite on its surface and acidic properties

Commercial mordenite was partially dealuminated in HCl medium by conventional heating or under microwaves by refluxing or autoclaving at 373 K at different times. Samples were characterized by AAS, XRD, N2 physisorption, FT-IR, 27Al NMR, NH3–TPD, and SEM techniques. The acidity of the dealuminated samples was also determined by testing them as catalysts in two acid catalysed reactions: the isomerization of styrene oxide to obtain β-phenylacetaldehyde, and the styrene oxide ring-opening reaction to give 2-ethoxy-2-phenylethanol. The use of microwaves, under autoclave or refluxing conditions, enhances dealumination, favours the later elimination of the Al extracted during washing, and affects the surface and acidic characteristics of the resulting samples. All catalysts showed similar low amounts of Brønsted acid sites. However, the catalyst treated under microwaves by autoclaving at shorter time (15 min) presented active acid centres with medium strength, and interestingly, lower amounts of strong Lewis acid sites (responsible for deactivation) than the rest of catalysts. These characteristics explain the total conversion obtained for this catalyst for the styrene oxide ring-opening reaction.