Plasma-Catalytic Oxidation of Toluene on MnxOy at Atmospheric Pressure and Room Temperature

Mn_xO_y/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N₂ adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, and O₂ temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn²⁺, Mn³⁺, and Mn⁴⁺), with Mn³⁺ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N₂ and 80 % N₂ + 20 % O₂ plasma, showing that the toluene removal efficiency and CO₂ selectivity were noticeably increased by Mn_xO_y/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO₂ in the N₂ plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the Mn_xO_y/SBA-15 surface; gas-phase O₂ subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn₂O₃ was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn₃O₄ mediated transfer of oxygen between the catalyst and toluene.