Investigation into the Structure and Properties of Biochar Co-Activated by ZnCl₂ and NaHCO₃ under Low Temperature...

Using sodium lignosulfonate as feedstock, ZnCl₂ and NaHCO₃ co-activated the hierarchical porous carbons (HPCs) were prepared by one-pot pyrolysis with different NaHCO₃ dosages (0-4 g) and carbonization temperatures (400-600 °C). Subsequently, phosphotungstate (HPW) was supported with the resulting biochar for the α-pinene hydration reaction to produce α-terpineol. The optimum preparation conditions were determined according to the yield of α-terpineol. The formation mechanism and physicochemical properties of HPCs were analyzed through TG, SEM, XPS, XRD, FT-IR, and N₂ adsorption-desorption isotherms. The results demonstrated that NaHCO₃ underwent a two-step reaction which liberated a substantial quantity of CO₂, thereby enhancing activated carbon's macroporous and mesoporous structures. Simultaneously, NaHCO₃ mitigated strong acid gas (HCl) emissions during ZnCl₂ activation. Compared with AC450-4:8:0 prepared by ZnCl₂ activation alone, the total pore volume of AC450-4:8:2 prepared by co-activation is increased from 0.595 mL/g to 0.754 mL/g and the mesopore rate from 47.7% to 77.8%, which is conducive to reducing the steric hindrance of the hydration reaction and improving the selectivity. Hydration experiments show that the selectivity of α-terpineol is 55.7% under HPW/AC450-4:8:2 catalysis, higher than 31.0% for HPW and 47.4% for HPW/AC450-4:8:0.