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, PW₁₂@GF, has been fabricated by immobilizing H₃PW₁₂O₄₀ (PW₁₂) 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 PW₁₂@GF, and the delocalized protons connect POM and GF into a stable composite. Importantly, biodiesel production is effectively promoted by PW₁₂@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 PW₁₂@GF (conversion: 97 %) in the heterogeneous system is even comparable to that of homogeneous PW₁₂ and strong Brønsted acidity and the lipophilic surface of the catalyst account for the excellent performance.