Included H3PW12O40 in cyclodextrin as catalyst for oleic acid esterification

Abstract

This study focuses on the use of cyclodextrins (β-CD and HP-β-CD) as host materials to immobilize 20 wt% tungstophosphoric acid, H₃PW₁₂O₄₀ (HPW), and their application as catalysts for the esterification of oleic acid, a fatty acid commonly found in many vegetable oils and frequently used as a biodiesel feedstock, into methyl oleate using methanol, the most commonly preferred alcohol for this reaction. The catalytic performances of these hybrid materials were compared with those of incorporated HPW into polyacrylamide hydrogel (20 wt% HPW/PAAm) and supported HPW on silica (20 wt% HPW/SiO₂), a conventional inorganic support. All materials were characterized by various techniques. For all supports, the Keggin structure of H₃PW₁₂O₄₀ was retained after immobilization, as confirmed by FT-IR and Raman spectroscopies. XRD and SEM analyses suggested the formation of inclusion complexes in the HPW/β-CD and HPW/HP-β-CD systems, as well as the successful incorporation of HPW into the PAAm matrix. In the esterification reaction carried out at 60 °C for 3h, bulk HPW, HPW/PAAm and HPW/β-CD exhibited high catalytic activity, achieving methyl oleate yields of 97, 94 and 69%, respectively, significantly higher than that obtained with the silica-supported catalyst (41%).