Tin-Functionalized Wood Biochar as a Sustainable Solid Catalyst for Glucose Isomerization in Biorefinery

This study tailored a novel engineered biochar as a solid catalyst for glucose isomerization by pyrolyzing Sn-functionalized wood waste under varying hypothesis-driven selected conditions (i.e., 650, 750, and 850 °C in N2 and CO2 atmosphere). The results showed that properties of biochar support (e.g., porosity and acid/base property) and chemical speciation of Sn were highly related to their catalytic performance. Variations in pyrolysis temperature and feed gas modified the porous structure and surface functionality of biochar as well as the valence state of doped Sn on the biochar. For the N2 biochars, higher pyrolysis temperature enhanced the fructose yield yet had trivial effect on the selectivity, where 12.1 mol % fructose can be obtained at 150 °C and 20 min using biochar produced at 850 °C. This was plausibly attributed to the increased fraction of amorphous Sn structures and metallic Sn that were more reactive than its oxide form. At the pyrolysis temperature of 750 °C, the use of CO2 increased the surface area by 40%, enlarged the pore volume from 0.062 to 0.107 cm3 g–1, and enriched the amorphous Sn structures compared to those for N2 biochar. This probably accounted for the better catalytic performance of CO2 biochar than that of N2 biochar (∼50% and 100% enhancement in fructose yield and selectivity, respectively). The Sn-biochar catalysts may have promoted glucose isomerization via both the Lewis acid and Brønsted base pathways. This study paves a new way to design biochar as a sustainable and low-cost solid catalyst for biorefinery applications.