Dramatically promoted toluene destruction over Mn@Na-Al₂O₃@Al monolithic catalysts by Ce incorporation: Oxygen vacancy construction and reaction mechanism

Here, a series of Mn-Ce binary oxides loaded monolith catalysts, with the support consisting of Na-Al₂O₃ grown on Al mesh obtained by steam vapor treating, were prepared to attain efficient toluene destruction. On increasing CeO₂ loading, the toluene conversion over prepared catalysts shows an exponential rise, with Mn-4Ce@Na-Al₂O₃@Al monolithic catalyst exhibiting the optimal performance, over which 90% of toluene can be decomposed at 239 °C with oxidation rate over 5.57 × 10⁻⁷ mol·g⁻¹·s⁻¹, obviously higher than those over 4Ce/Na-Al₂O₃@Al (239 °C; 0.99 × 10⁻⁷ mol·g⁻¹·s⁻¹) and Mn/Na-Al₂O₃@Al (291 °C; 4.12 × 10⁻⁷ mol·g⁻¹·s⁻¹). H₂-TPR and XPS results reveal that the superior redox ability and the formation of MnCeO_x solid solution are favorable for toluene abatement. Oxygen vacancies form easily on the surface of Ce modified samples, resulting in superior oxygen and toluene adsorption ability, as demonstrated by DFT theoretical calculation. Besides, the pathways of toluene oxidation over Mn-4Ce@Na-Al₂O₃@Al catalyst were identified by using the in situ DRIFTS, and the key intermediates of toluene oxidation reaction are determined to be benzoyl, benzaldehyde, and benzoate.