Engineered rice-straw biochar catalysts for the production of value-added chemicals from furan

In this study, biochars produced in two different atmospheres were used as catalysts for the valorization of furan, which derives from the hemicellulosic component of waste biomass. The biochars were produced from rice straw via pyrolysis in either an N2 or a CO2 environment (RSB-N2 or RSB-CO2) to modify their surface area and porosity. The biochars were then employed as a catalyst to support a bifunctional Ru–ReOx catalyst. The biochar-supported Ru–ReOx catalysts (Ru–ReOx/RSB) were compared to a conventional activated charcoal (AC)-supported Ru–ReOx catalyst (Ru–ReOx/AC). The biochar-supported catalysts exhibited differences in reducibility and contained a different form of Re species compared to the AC-supported catalyst, which was attributed to the presence of alkali metal (e.g., potassium) in the biochar catalysts. The reducibility and metal dispersion on the support were also strongly associated with the atmosphere under which the biochar was produced. In particular, the Ru–ReOx/RSB-CO2 catalyst consumed 24% more hydrogen than did the Ru–ReOx/RSB-N2 catalyst within a temperature range of 250 to 560 °C. The biochar-supported catalysts had 12 times fewer surface metal sites than did the AC-supported catalyst due to their lower surface area. The reaction rate on a per-site basis for the conversion of furan to tetrahydrofuran and 1,4-butanediol was also measured for the catalysts. The Ru–ReOx/RSB-N2 catalyst was twice as active as the Ru–ReOx/RSB-CO2 catalyst and three times more active than the Ru–ReOx/AC catalyst. This study thus proposes a straightforward strategy for modifying the catalytic properties of biochar catalysts and suggests a new application of biochar in the production of value-added chemicals from biomass and waste. The results also highlight the potential of biochar as a replacement for conventional catalysts in biorefineries.