Reheat treatment under vacuum induces pre-calcined α-MnO2 with oxygen vacancy as efficient catalysts for toluene oxidation

Abstract

Engineering α-MnO2 with abundant oxygen vacancies is efficient to enhance its catalytic activity towards toluene oxidation. A simple and facile method was introduced to fabricate oxygen vacancies on α-MnO2 surface by reheating the pre-calcined samples under vacuum condition. The reheat treatment especially at 180 °C is beneficial for the formation of oxygen vacancies on α-MnO2 surface, enhancing the oxidation of toluene. The toluene conversion is up to 100% at 270 °C, which is 30 °C lower than that of α-MnO2 without reheat treatment. The apparent activation energy (16.8 kJ mol−1) of MnO2-180 catalyst is lowest among these catalysts, which is essential for accelerating the oxidation of toluene. In-situ DRIFTS results indicate that the MnO2-180 sample promotes the formation of benzaldehyde and the occurrence of ring-opening reaction, thus effectively improving the catalytic performance for toluene oxidation. A possible catalytic oxidation mechanism of toluene over α-MnO2 catalysts after reheat treatment was proposed.