Preparation of mesoporous polyoxometalate-tantalum pentoxide composite catalyst and its application for biodiesel production by esterification and transesterification

Abstract

Mesoporous polyoxometalate-tantalum pentoxide composite catalyst, H₃PW₁₂O₄₀/Ta₂O₅, with H₃PW₁₂O₄₀ loading from 3.6 to 20.1% was prepared by a one-step sol–gel-hydrothermal route in the presence of a triblock copolymer surfactant. Bulk and surface sensitive probe testing results indicated that the primary Keggin structure remained intact after formation of the composite, and strong interaction between the Keggin unit and Ta₂O₅ framework existed in the composite. Additionally, the composite exhibited larger and well-distributed three-dimensionally interconnected pores (3.9–5.0 nm), larger BET surface area (106.0–126.9 m² g⁻¹), high porosity (0.44–1.37 cm³ g⁻¹), and homogeneous dispersion of the Keggin unit throughout the composite. As an environmentally friendly solid acid catalyst, the catalytic performance of the H₃PW₁₂O₄₀/Ta₂O₅ was evaluated in the esterification of lauric acid and myristic acid, the transesterification of tripalmitin as well as the direct use of soybean oil for biodiesel production. Regardless of the presence of free fatty acids, the H₃PW₁₂O₄₀/Ta₂O₅ composite showed high reactivity and selectivity towards simultaneous esterification and transesterification under mild conditions. The catalyst can be recovered, reactivated and reused several times.