Facile synthesis of microcellular foam catalysts with adjustable hierarchical porous structure, acid–base strength and wettability for biomass energy conversion†
Herein we report a novel synthetic strategy for fabrication of microcellular foam catalysts (MFCs) with hydrophobic, acid–base, and hierarchical porous properties for conversion of one-pot cellulose to a key chemical platform (i.e. 5-hydroxymethylfurfural, HMF) for biofuels. The water-in-oil (W/O) Pickering high internal phase emulsions (HIPEs), stabilized by both amino-functionalized nanoparticles (namely, S-NH2) and Span 80, were used as the template for simultaneous polymerization of oil phase containing 1-octene, divinylbenzene (DVB), and trihydroxymethylpropyl trimethylacrylate (TMPTMA). After subsequent sulfonation process, acid and base sites resulting from grafted –SO3H group of polydivinylbenzene (PDVB) and S-NH2 were both located on the surface of the MFCs. The resultant MFCs composite had a typical hierarchical porous structure, and the macropores with a well-defined open-cell and interconnecting pore throat structure could be controlled via the composition of the oil phase of emulsion, with the mesopore structure closely related to the degree of cross-linking of oil-soluble functional monomer. The representative catalyst MFCs-3 had a hierarchical porous structure (macropores ranging from 1.0 µm to 30 µm and uniform mesopores in 32.1 nm), hydrophobic surface (water contact angle of 125°), 0.735 mmol g−1 of base, and 1.305 mmol g−1 of acid. The HMF yield of 41% for cellulose conversion showed its excellent catalytic performance. This work opens up a route for simple and controlled fabrication of multifunctional polymeric catalysts for biomass energy conversion.