Assembly of polyoxometalate with graphene foam as a compressible monolithic catalyst for biodiesel production

Compressible monolithic catalysts exhibit remarkable advantages over traditional powder ones, but the fabrication of polyoxometalate (POM)-containing compressible catalyst is rarely explored. Herein, a compressible monolith, PW 12 @GF, has been fabricated by immobilizing H 3 PW 12 O 40 (PW 12 ) catalyst on elastic graphene foam (GF). Moreover, FT-IR and XPS spectra analysis and leaching test reveal that the delocalization of protons on POM occurs during the assembly of PW 12 @GF, and the delocalized protons connect POM and GF into a stable composite. Importantly, biodiesel production is effectively promoted by PW 12 @GF under mild conditions (60 °C) without stirring, and the product can be easily separated from the catalyst by compression. Moreover, its catalytic activity is basically maintained after five cycles. Notably, the catalytic activity of PW 12 @GF (conversion: 97 %) in the heterogeneous system is even comparable to that of homogeneous PW 12 and strong Brønsted acidity and the lipophilic surface of the catalyst account for the excellent performance.