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 ZrO(OH)(CHCOO) and low-temperature self-assembly-has been adopted to synthesize the PW@UIO-66 composite (PW = HPWO; UIO-66 = ZrO(OH)(OOC-CH-COO)). The as-synthesized PW@UIO-66 composite exhibits highly crystalline, good octahedron morphology, large specific surface area (1960 m g) and high thermal stability (>500 °C), which clearly demonstrates the potential as a solid-acid catalyst. Additionally, the PW@UIO-66 composite may be accomplished with 85% utilization of HPWO and 95% yield through this synthetic procedure. The performances of the PW@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@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@UIO-66 composite remained unchanged and in the meantime the PW@UIO-66 composite still maintained a high activity to convert soybean oil into biodiesel.