Hierarchically Macro-/Mesoporous Polymer Foam as an Enhanced and Recyclable Catalyst System for the Sustainable Synthesis of 5-Hydroxymethylfurfural from Renewable Carbohydrates

Renewable and abundant carbohydrates are being strongly focused upon as a green and sustainable alternative for the production of valuable chemicals and biofuels. In this study, we chemically integrated acid-base bifunctionalized mesoporous silica nanoparticles (MSNs-SO3H-NH2) and a macroporous polymer foam poly(HIPE) (PH) matrix that is derived from water-in-oil (W/O) high internal phase emulsion (HIPE) templating. After the subsequent sulfonation process, a SPHs@MSNs-SO3H-NH2 catalyst with a hierarchical porous structure and bifunctional sites was prepared and used for the highly efficient synthesis of top value-added 5-hydroxymethylfurfural (HMF) from renewable cellulose in an ionic liquid (i.e., 1-ethyl-3-methylimidazolium chloride, [EMIM]Cl) based system. Evaluation of the catalytic activity revealed that the designed macropores were favorable for ready mass transfer, whereas the high surface area for active-site anchoring provided by the mesoporous structure was beneficial in enhancing the catalyst performance. A theoretical study also suggested that acidic and basic active sites synergistically work for the transformation reaction. Under the optimized conditions, a remarkably high HMF yield (44.5%) was obtained efficiently. Furthermore, the as-prepared catalyst was recycled in four consecutive cycles with a total loss of only 4.9% activity.