Lignocellulosic biomass is a promising renewable resource for the production of numerous key commodity chemicals, including 5-hydroxymethylfurfural (5-HMF), that can be sourced from its cellulose component via a three-step reaction promoted by both Brønsted and Lewis acid sites 1. Given the highly oxygenated nature of biomass, carbon-based catalysts are one of the best possible systems for favouring this transformation, thanks to their superior mechanical and chemical resistance in this specific media, along with controlled and tuneable textural and surface features. In the present work, bifunctional carbon-based acid catalysts were successfully synthesized by co-locating mesoporous aluminosilicate patches 2-3 and benzyl sulfonic moieties 4 on the substrate’s surface (activated carbon powder (AC), fraction < 50μm), conferring both Brønsted and Lewis acidity to the same solid. These bifunctional catalysts and their monofunctional equivalents (sulfonated carbon and aluminosilicate patched carbons) were then fully characterized and compared in terms of catalytic activity. SEM/EDX, TEM, and XPS analyses were carried out to investigate the achieved composition and morphology, whereas nitrogen physisorption and Boehm titration were performed to study the attained textural features and acidity, respectively. Finally, the catalytic performance of all the synthesized systems was investigated for the upgrading of cellobiose to 5-HMF. A proximity effect was found when the two acidic sites were combined onto the same substrate, facilitating the overall conversion of the sugars involved in comparison to the designed mixtures of monofunctional solids tested. A maximal yield of 37% of 5-HMF was attained after 23 h with catalyst AC–aluminosilicate/SO3H in a THF:mQ water system at 423 K. No significant traces of side products were observed after 23 hours, indicating the satisfactory selectivity of the catalyst for the targeted sugars.
Tonelli et al. (Wed,) studied this question.