Kiwi twig biochar recycling promoting the reduction of NO by a MnO₂ catalyst

Kiwi twigs have abundant vessels and sieve tubes, which may provide abundant nanotube structures and active sites. In this study, kiwi twig biochar was used to modify the α-manganese dioxide (MnO₂) catalyst through facile potassium hydroxide solution (KOH) activation to improve N₂ selectivity in selective catalytic reduction (SCR). Results suggested that the C1_0.5MnO₂ catalyst exhibited higher NO conversion (approximately 90%) and N₂ selectivity (>95%) at 100 °C–250 °C. Moreover, biochar C1, which was directly mixed with KOH, increased the number of acid sites and lattice defects in the C1_0.5MnO₂ catalyst; thus, the redox and acid cycles more easily occurred on the surface of the C1_0.5MnO₂ catalyst than on that of the C2_0.5MnO₂ catalyst. Moreover, the SCR process of the modified catalysts involved both Langmuir–Hinshelwood and Eley–Rideal mechanisms. This study demonstrated the effect of biochar on reaction sites and processes, providing a new perspective for the application of biochar in the field of catalysis.