Taming the Activation Routes Achieves Highly Efficient Toluene Degradation by H₂-Induced Hydrodealkylation

Catalytic oxidation of industrial aromatic hydrocarbons at low temperatures is still a challenge. In this work, we found that H₂ can significantly promote toluene oxidation over Pt/TiO₂ catalyst by intrinsically altering the reaction route, with the temperature at conversion of 90% (T₉₀) decreasing from 199 to 146 °C and apparent activation energy reducing from 109.2 to 38.6 kJ·mol⁻¹. Moreover, CO₂ selectivity increases to 100% at 180 °C, which is much higher than that without H₂ (just 30.2%). H₂ also benefits maintenance of Pt⁰ in the reaction and thus promotes catalyst stability. Based on the results of temperature-programmed surface reaction, in situ DRIFTS, in situ Raman, and theoretical calculations, the toluene oxidation mechanism over Pt/TiO₂ changes greatly after the addition of H₂. Without H₂, −CH₃ of toluene is oxidized first, and the reaction pathway follows a traditional way of toluene → benzyl alcohol → benzaldehyde → benzoic acid → maleic acid → CO₂ and H₂O. However, the C−C bond of toluene is broken first in the presence of H₂, and benzene is formed by the hydrodealkylation process. The reaction mainly follows the pathway of toluene → benzene → phenol → benzoquinone → maleic acid → CO₂ and H₂O. In addition, H₂ also significantly promotes the oxidation of p-, m-, o-xylene, and ethylbenzene. This work sheds a new viewpoint to realize the low-temperature and eco-friendly purification of toluene and benefits the development of efficacious catalytic systems toward volatile organic compound degradation.