Insight into the Mechanism of α-, β-, γ-, and δ-MnO₂ in Catalyzing Ammonium Perchlorate Decomposition: Superoxide...

To date, the catalytic mechanism of metal oxides in the thermal decomposition of ammonium perchlorate (AP) remains unclear and hinders the design and manufacture of efficient AP catalysts. Herein, a catalytic mechanism of the superoxide promotion (SOP) effect is reported, and the more oxygen vacancies and the lower band gaps of the catalysts allow deep decomposition of AP by •O₂^-. With the addition of 2 wt % δ-MnO₂, the HTD temperature of AP decreases from 419.4 to 298.8 °C, and the ΔH increases from 585.5 to 1446.0 J g^-1. The SOP effect accelerates the thermal decomposition of AP at low temperatures. Moreover, density functional theory (DFT) calculations confirm that the elongation of the O-O bond (1.34 Å) facilitates the activation of the O₂ adsorbed on these vacancies. δ-MnO₂ shows the most powerful SOP effect; thus, it is one of the best catalysts for AP thermal decomposition. In addition, ΔT and the ratio of NO₂/N₂O are highly correlated with •O₂^-; these results indicate that the diverse catalytic activity exhibited by the different crystal phases of MnO₂ on AP is caused by the differences in the SOP effect.