Two-step preparation of Keggin-PW@UIO-66 composite showing high-activity and long-life conversion of soybean oil into biodiesel

A polyoxometalate acid can be encapsulated into a metal-organic framework to construct a novel kind of solid-acid catalyst. In this work, the two-step method -high-temperature preparation of Zr 6 O 4 (OH) 4 (CH 3 COO) 12 and low-temperature self-assembly-has been adopted to synthesize the PW 12 @UIO-66 composite (PW 12 = H 3 PW 12 O 40 ; UIO-66 = Zr 6 O 4 (OH) 4 (OOC-C 6 H 4 -COO) 12 ). The as-synthesized PW 12 @UIO-66 composite exhibits highly crystalline, good octahedron morphology, large specific surface area (1960 m 2 g −1 ) and high thermal stability (>500 °C), which clearly demonstrates the potential as a solid-acid catalyst. Additionally, the PW 12 @UIO-66 composite may be accomplished with 85% utilization of H 3 PW 12 O 40 and 95% yield through this synthetic procedure. The performances of the PW 12 @UIO-66 composite are investigated by catalyzing the simultaneous transesterification and esterification of soybean oil into biodiesel. Under the optimal conditions, the conversion of the soybean oil into biodiesel would exceed 90% over the as-synthesized PW 12 @UIO-66 composite. As the crucial indexes for industrial prospects, the recycling and life experiments were surveyed. After 10 times recycling and 4 weeks, the structure and performance of the PW 12 @UIO-66 composite remained unchanged and in the meantime the PW 12 @UIO-66 composite still maintained a high activity to convert soybean oil into biodiesel. A Keggin-PW 12 @UIO-66 composite has been synthesized solvothermally through a two-step process and employed as a solid acid catalyst to convert soybean oil into biodiesel.