Effect of Phosphate Stabilizers in Hydrogen Peroxide Decomposition on Manganese-Based Catalysts

Adverse effects of phosphate ions used as a stabilizing agent in rocket-grade hydrogen peroxide on the decomposition catalyst were investigated. For a comparative study, MnO2/Al2O3 and MnO2+PbO/Al2O3 were selected as the catalyst to decompose 90 wt% hydrogen peroxide containing 1.24 mg/liter of phosphate ions. The reactivity of the catalysts measured by reactivity tests decreased by half in the hydrogen peroxide, including phosphate ions. Endurance of the catalyst was evaluated on a 50 N monopropellant thruster by measuring the chamber pressure. The degradation of the decomposition efficiency of the catalyst was evident after the initial 5 s, during which the lead-doped catalyst revealed better performance than the pure MnO2 catalyst. After 30 s of thruster operation, performance degradation was particularly severe with the lead-doped catalyst. The catalysts sampled after thruster operation were characterized by mass analysis, the Brunauer Emmet Teller model, and energy dispersive spectroscopy. A large quantity of phosphorus was detected on both catalysts tested with a high concentration of phosphate ions. The amount of phosphorus detected on the lead-doped catalyst was four times as large as the amount of phosphorus on the pure MnO2 catalyst, indicating the affinity of lead and phosphate. The accumulation of phosphate on the catalyst surface inhibited the contact of hydrogen peroxide and the active material, preventing efficient decomposition.