Nanostructured Mn-Substituted Lanthanum Hexaaluminate with Enhanced Thermal Stability and Catalytic Activity for Decomposition of Hydroxylamine Nitrate Propellant

Developing highly efficient and stable catalysts for hydroxylamine nitrate (HAN) decomposition is challenged by their tendency to sinter and suffer a sharp loss in specific surface area at high temperatures. Herein, a series of manganese-substituted lanthanum hexaaluminate (LMxA, x = 0, 0.5, 1, 2, 3) nanomaterials were prepared by coprecipitation-decarbonization templating method, and the effect of manganese doping on structure and the catalytic activity for HAN decomposition were systematically investigated. XRD and BET characterization revealed that the manganese substitution significantly regulated the structural properties of hexaaluminate nanomaterials, among which pure-phase LaMnAl11O19 (denoted as LM1A) exhibited excellent high-temperature structural stability. After calcination at 1400 °C for 12 h, the grain size increased only slightly from 24.1 to 28.7 nm, and the specific surface area retained at 15.8 m2·g–1, indicating outstanding resistance to nanoparticle sintering. Notably, LM1A served dual roles as both a catalytic support and an active component, exhibiting a stable catalytic efficiency for HAN decomposition, which could significantly reduce the initial decomposition temperature from 162.0 °C (thermal decomposition) to 120.4 °C. Manganese doping lowers the reaction energy barrier, as confirmed by critical kinetic parameters. Rational nanoscale regulation of manganese doping in hexaaluminate significantly enhances the high-temperature stability, providing an important reference for the development of highly efficient and long-life HAN decomposition catalysts.