Catalytic Oxidation Mechanism of Toluene over Ce (x) Mn1-x O2: The Role of Oxygen Vacancies in Adsorption and Activation of Toluene

Catalytic oxidation has been extensively studied as apromisingtechnology for the removal of toluene from industrial waste gasesand indoor air. However, the debate regarding the oxidation mechanismis far from resolved. Ce (x) Mn1-x O2 catalysts with different mixing ratiosare prepared by the sol-gel method and found to exhibit bettercatalytic activities for toluene oxidation than a single oxide. Characterizationsand theoretical calculations reveal that the doped Mn increases thenumber of oxygen vacancies and the ability of oxygen vacancies toactivate aromatic rings, which promotes the rate-determining stepof toluene oxidation, i.e., ring-opening reactions.The oxidation products detected by in situ diffusereflectance infrared Fourier transform spectroscopy (DRIFTS) and Vocusproton transfer reaction mass spectrometry (Vocus-PTR-MS) show thatthe doped Mn significantly improves the ring-opening efficiency andsubsequently yields more short-chain products, such as pyruvic acidand acetic acid. A comprehensive oxidation pathway of toluene is refinedin this work.