Elucidating the structure-activity relationship of Bi-doped MnO2 catalysts towards CH3OH oxidation

MnO₂-based catalysts have been extensively utilized in the catalytic oxidation of volatile organic compounds due to their cost-effectiveness. In this study, a series of Bi-doped MnO₂ catalysts with various contents were systematically investigated to reveal the structure-activity relationship during the CH₃OH oxidation reaction, which was achieved using a series of characterizations. Bi could enter the MnO₂ lattice and lead to the facile formation of oxygen vacancies, facilitating the generation of surface reactive oxygen species by O₂ dissociation. With the increase of Bi, the activity showed a volcanic trend, and the Mn_7.5Bi₁O_x (T₉₀ = 160 °C) exhibited the lowest apparent activation energy and optimal performance. CH₃OH oxidation mechanism (CH₃OH → methoxy species → formate species → CO₂ and H₂O) was revealed by in situ DRIFTS, and the last two oxidation processes were significantly sped up. Bi-doped MnO₂ exhibited high H₂O tolerance due to hydroxyl-assisted CH₃OH chemisorption via hydrogen bonding and hydroxyl-assisted C-H activation of methoxy species with surface reactive oxygen species. These findings are beneficial for the rational design of metal-doped catalysts with rich oxygen vacancy defects for catalytic oxidation.