Interplay effect on simultaneous catalytic oxidation of NOx and toluene over different crystal types of MnO2 catalysts

This paper firstly investigated the interplay effect on simultaneous catalytic oxidation of NO and toluene. Four tunnel-structure polymorphs, i.e., α-MnO₂, β-MnO₂, γ-MnO₂ and δ-MnO₂, were synthesized to compare individual and simultaneous oxidation of NO and toluene. Results demonstrated that toluene significantly inhibited NO conversion that near zero efficiencies were observed at low temperature over the four catalysts. Subsequently, NO oxidation efficiency climbed rapidly to the equivalent value as absence of toluene. In addition, presence of NO also elevated toluene conversion into higher temperature of 10–20 °C than that without NO. The reaction between toluene and oxygen took the superiority during simultaneous oxidation with NO. NO oxidation efficiency started to increase until toluene degradation approaching to the equilibrium. However, this competition seemed to be negligible at high temperature that both toluene and NO attained high conversion efficiencies. These findings provide a feasible way for simultaneous removal of NO_x and VOCs using catalytic oxidation as well as selecting an optimal temperature window.