Catalytic Oxidation Mechanism of Toluene over Ce<i><sub>x</sub></i>Mn<sub>1–<i>x</i></sub>O<sub>2</sub>: The Role of Oxygen Vacancies in Adsorption and Activation of Toluene
Wenshuo Zhou, Heping Li, Boying Song, Wei Ma, Zhikun Liu, Zongcheng Wang, Zhongjun Xu, Liwei Meng, Yafei Wang, Xiaoxiao Qin, Changbin Zhang, Qiong Tang, Xiaolei Bao, Kuo Liu, Hui Li, Yongchun Liu
Abstract
Catalytic oxidation has been extensively studied as a promising technology for the removal of toluene from industrial waste gases and indoor air. However, the debate regarding the oxidation mechanism is far from resolved. Ce x Mn 1– x O 2 catalysts with different mixing ratios are prepared by the sol–gel method and found to exhibit better catalytic activities for toluene oxidation than a single oxide. Characterizations and theoretical calculations reveal that the doped Mn increases the number of oxygen vacancies and the ability of oxygen vacancies to activate aromatic rings, which promotes the rate-determining step of toluene oxidation, i.e., ring-opening reactions. The oxidation products detected by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Vocus proton transfer reaction mass spectrometry (Vocus-PTR-MS) show that the doped Mn significantly improves the ring-opening efficiency and subsequently yields more short-chain products, such as pyruvic acid and acetic acid. A comprehensive oxidation pathway of toluene is refined in this work.