Ball-milled, solvent-free Sn-functionalisation of wood waste biochar for sugar conversion in food waste valorisation

The use of biomass wastes for biochar production is a promising waste management option, and biochars can be potentially applied in the food waste recycling industry to produce value-added chemicals. In this study, an advanced Sn-functionalised biochar catalyst was synthesised via a novel solvent-free ball milling protocol to facilitate the isomerisation of glucose to fructose. Raw wood biomass (W) and its derived biochars pyrolysed at low (LB, 400 °C) and high (HB, 750 °C) temperatures were investigated as catalyst supports. The interactions between Sn and the carbonaceous supports were related to the surface chemistry of the catalysts. The raw W had a functional group-enriched surface, which provided more active sites for anchoring Sn, resulting in higher metal loading on the support compared to LB and HB. The annealing temperature was another critical factor determining the amount and speciation of loaded Sn. Catalytic conversion experiments indicated that SnW annealed at 750 °C exhibited the best fructose yield (12.8 mol%) and selectivity (20.2 mol%) at 160 °C for 20 min. The catalytic activity was mainly determined by the quantity and nature of active Sn sites. This study elucidated the roles of the carbon support and its surface chemistry for synthesising biochar-supported catalysts, highlighting a simple and green approach for designing effective solid catalysts for sustainable biorefineries.