Engineering oxygen vacancies in metal-doped MnO2 nanospheres for boosting the low-temperature toluene oxidation

Abstract

Promoting the catalytic activity by engineering oxygen vacancies is a fascinating strategy in heterogeneous catalysis. Herein, a series of metal oxide catalysts with different metal doping were prepared through a redox precipitation method to regulate oxygen vacancies in MnO2 and tested in toluene catalytic oxidation at low temperature. To accurately elaborate the structure–activity relationship of different catalysts, the prepared catalysts were systematically characterized by various techniques. Results showed that the doped metals entered the MnO2 skeleton as expected and resulted in the lattice distortion, as well as oxygen vacancies. The catalyst Cu-MnO2, which was obtained by doping Cu into MnO2, had the most oxygen vacancy contents and increased oxygen migration mobility, thus showing the best catalytic toluene oxidation activity at low temperature (T90 = 219 °C). Meanwhile, in-situ DRIFTs demonstrated the intermediates like benzene methanol, benzaldehyde, benzoic acid, maleic acid generated at different environments and revealed that the rate-controlling step probably be the deep oxidation of benzoate species. In addition, the supplement of gas phase oxygen played an important role in the complete transformation of the intermediate benzoic acid. This work open up an attractive method for acquiring metal-doped MnO2 nanospheres catalysts for toluene oxidation.