Synthesis and evaluation of macroporous polymerized solid acid derived from Pickering HIPEs for catalyzing cellulose into 5-hydroxymethylfurfural in an ionic liquid

Stable water-in-oil (W/O) Pickering high internal phase emulsions (HIPEs) with an internal phase volume fraction of 84.8% were first stabilized by both the hydrophobic silica nanoparticles and span 80. Then, based on the obtained Pickering HIPEs, several macroporous polymerized solid acid (PDVB-SS-X-SO3H, X = 0, 0.2, 0.6) were prepared by polymerizing divinyl benzene (DVB) and sodium p-styrenesulfonate (SS), and were subsequently combined with sulfonation in H2SO4. All the as-prepared PDVB-SS-X-SO3H possessed open-cell structure, interconnecting pores and strong acidity, and were adopted as catalysts to convert cellulose into 5-hydroxymethylfurfural (HMF) in the presence of [Emim]Cl-mediated solvents. The results showed a maximum yield of 29.6% for PDVB-SS-0.2-SO3H, 12.9% for PDVB-SS-0-SO3H and 15.5% for PDVB-SS-0.6-SO3H under the same condition within 2.0 h at 120 °C, suggesting that the pore sizes and strong acidic sites played a key role in cellulose conversion. PDVB-SS-X-SO3H can be very easily recycled at least four times without a significant loss of activity. This research opens up a new method to synthesize porous solid acid catalyst materials through Pickering HIPEs templates.