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 (∼32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Brønsted 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 (Brønsted 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 °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 (∼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.

This work studied the influence of highly dispersive WOx species (observed by Raman spectroscopy) on USY zeolite structure, acidity and activity towards an esterification reaction.Figure optionsDownload as PowerPoint slideHighlights
► This work studied USY zeolite modified by WO3 impregnation for biodiesel production.
► WO3 incorporation decreases the amount and strength of the zeolite acidic sites.
► The material acidity was correlated with the oleic acid esterification activity.
► The catalytic cycles revealed that 11.4% WO3/USY was the most promising material.
► 11.4% WO3/USY showed better resistance to water and the highest turnover number.