Effects of impure ions in precursors on the formation of active oxygen in MnO₂ for promoting VOCs oxidation

Impure ions in the precursor can cause the structural transition of prepared MnO2 catalysts and influence their activity in toluene catalytic oxidation. Here, the effects of K+ and SO42- on the catalytic activity of MnO2 are examined. Removing absorbed SO42- by repeating water washing facilitates the exposure of active sites on the surface of MnO2. The temperature for toluene conversion reaches 90% (T90) of catalysts decreases from 247 degrees C to 238 degrees C. While the loss of K+ during the water washing leads to the inferior performance of MnO2. Reimpregnating of K+ can stimulate the generation of active oxygen species on the surface of catalysts (K/ MnO2), which showed elevated catalytic activity in toluene conversion (T90, 229 degrees C). In addition, K/MnO2 performs good stability for toluene combustion in long-term operation. Density Function Theory calculations reveal that the formation energy of oxygen vacancy and the adsorption energy of toluene on the surface of catalyst decrease from 6.996 eV and - 0.079 to 5.482 eV and - 0.468 eV as the introduction of K+, respectively. Our results provide a complete understanding of the effects of impurity ions on the performance of manganese oxide for catalytic oxidation of toluene.