Abstract
The alkali metal potassium has the functions of structure promotion and electronic modulation in metal oxides. Herein, diverse potassium precursors (KOH, KNO3, K2SO4, and KCl) were introduced to alpha-MnO2 nanorods through a facile post-processing strategy. The presence of potassium species has a remarkable promotion effect on the catalytic performance of alpha-MnO2. Amongst them, the KOH/MnO2 sample has the highest activity and can destroy 90% toluene (1000 ppm) at just 226 degrees C with a reaction rate of 3.39 x 10(-4) mol g(cat)(-1) s(-1), which is over 20 times higher than that of pure alpha-MnO2. Different anions in the potassium precursors bring a distinct mutation in the alpha-MnO2 structure, promote the formation of MnO6-K-MnO6 bridging bonds in alpha-MnO2, and exhibit obvious diverse abilities for balancing charge transfer. KOH is identified as the most promising precursor for alkali metal modification, which significantly improves the distribution of K species over the alpha-MnO2 surface and strengthens the content and activity of lattice oxygen. It is confirmed that the lattice oxygen plays a key role in the catalytic oxidation of toluene over alpha-MnO2, which follows the Mars-van Krevelen mechanism. Positive hole defects (Mn3+) caused by KOH treatment play an important role in the diffusion of O and enhance the reducibility of manganese oxide. In addition, the enhanced specific surface area, pore volume, and surface acidity are also conducive for the catalytic oxidation of toluene.