Structural effects of WO3 incorporation on USY zeolite and application to free fatty acids esterification

Zeolites have occupied a distinguished position due to their unique properties as solid acids and catalytic results achieved in several industrial reactions. This work studied the influence of supported WO3 on USY zeolite structure, acidity and activity towards an esterification reaction. High dispersion of WO3 species on USY was achieved, but at higher loading (>= 11.4%), microcrystalites of WO3 were detected below the theoretical monolayer coverage (similar to 32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Bronsted sites of USY as well as on silanol surface groups with the formation of small aggregates. In addition, dealumination took place, especially in the samples with high WO3 loading. USY had the most and the strongest acidic sites (Bronsted type), but the incorporation of WO3 decreased the amount and the strength of the new sites. However, all WO3/USY catalysts were more active than USY in the esterification of oleic acid with ethanol (conversion above 74%, 2 h at 200 degrees C). The calculation of the TOF for a 1 h reaction demonstrated that 11.4% WO3/USY was the most active catalyst. Furthermore, it had the lowest rate of deactivation of acid sites after the reaction (similar to 13% after four cycles). The better performance of the 11.4% WO3/USY sample was also attributed to a better distribution of strength of the acidic sites and a more hydrophobic character of the synthesized material. (C) 2011 Elsevier Inc. All rights reserved.