Study on the catalytic decomposition of $N_2O$ to develop monopropellant thruster

Abstract

In the present study, catalytic decomposition of $N_2O$ for monopropellant thruster was carried out with three different catalysts (Ir, Pt and Ru). Preparation methods of the catalyst with different supports were described with measurement of the catalyst activity and comparison of characteristics. Three noble metal catalysts, Ir, Pt and Ru as active materials were used to prepare catalyst by wet-impregnation method with $γ-Al_2O_3$ as a catalyst support. Additionally, due to high temperature of $N_2O$ decomposition, thermally stable catalysts were prepared: Si-doped alumina prepared by impregnation (IMP), one-step catalyst synthesis (OS); and metal-substituted hexaaluminate prepared by using one-pot precipitation method. Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD) were used to analyze and determine catalysts’ surface morphology, structure and composition. Next, a 5N class thruster was designed to perform hot-fire tests with prepared catalysts. First, Ir, Pt and Ru on γ phase of $Al_2O_3$ were tested individually with different chamber pressures and preheating temperatures. During the tests, minimum required preheating temperature decreased as the chamber pressure increased. Thus, compared to Pt, Ir and Ru showed a lower decomposition temperature of $N_2O$ and a lower reaction observed at $230^circ C$. However, further experiments showed stable activation temperature of $300^circ C$ for Ir, while Ru showed repeatability at preheating temperature as low as $250^circ C$. In spite of the advantages over Pt, deactivation of the Ir and Ru catalyst was observed during the experiment. In case of θ and λ phase of $Al_2O_3$ supported Ru catalyst, decomposition of $N_2O$ required high preheating temperature $(>500^circ C)$. Lastly, Si-doped alumina and hexaaluminate supported Ir, Pt, Ru catalysts were investigated. The activity tests for the gas mixture containing $N_2O$ (28%, v/v) in Ar decomposition demon...