Performance evaluation of Ru–Pt alloy nanoparticle catalysts for hydroxylammonium nitrate (HAN)-based propellants†

Hydroxylammonium nitrate (HAN)-based propellants represent next-generation monopropellants for thrusters. Ruthenium is a promising catalytic material for HAN-based propellants, with the merits of high activity and relatively low price. However, ruthenium catalyst is unstable and prone to aggregation and oxidation. Herein, we prepared a Ru–Pt alloy nanoparticle (NP) catalyst via an impregnation method. The addition of Pt effectively delayed the deactivation of Ru. In order to understand the active components of the catalyst, both fresh and aged catalyst samples were characterized. The active species was identified as Ru⁰ species, which was gradually oxidized to Ru/RuO_x. In droplet and thruster tests, the Ru–Pt alloy NP catalyst exhibited a higher activity and stability than the Ru NP catalyst and successfully passed through the pulse and 100-second-long steady-state thruster tests, with good pulse consistency and low steady-state roughness. This work provides a promising pathway to explore low-cost catalysts for HAN decomposition.