ABSTRACT
Ammonium dinitramide (NH4N(NO3)2, ADN) is regarded as a promising oxidizer due to its low signature and high specific impulse. Generally, ADN undergoes exothermic decomposition above 140 °C accompanied by the byproduct of ammonium nitrate (AN). The inevitable endothermic decomposition of AN decreases the overall heat release, and so there is a need to develop efficient catalysts to guide ADN decomposition along desired pathways with a lower decomposition temperature and higher heat release. A suitable catalyst should be able to withstand the harsh conditions in a thruster to achieve a stable thrust force, which poses a huge obstacle for manufacturing a stable and active catalyst. This review gives a comprehensive summary of the thermal and catalytic decomposition pathways of ADN for the first time, which is expected to deepen the understanding of its reaction mechanism and provide useful guidance for designing prospective catalysts toward efficient ADN decomposition.
ABSTRACT
The poor thermodynamic stability of gold nanoparticles (NPs) makes it very challenging to stabilize them in small sizes at elevated temperatures. Herein, we report the preparation of antisintering Au nanocatalyst by rationally selecting the sublattice matched MgGa2O4 spinel as support based on theoretical predictions. Au/MgGa2O4 retains Au NPs of 2-5 nm even after aging over the melting temperature of bulk gold (1064 °C)! By identifying the stable structure, the extraordinary stability is found to arise from the formation of a new phase structure, namely Au-MgGa2O4 metal-oxide "hetero-bicrystal" that remains as crystallite without melting even at 1100 °C. More than 80% of the loaded Au can be efficiently stabilized so that the catalysts can exhibit excellent low-temperature activities for diesel exhaust (CO and C3H6) oxidation after severely thermal and hydrothermal aging. These results may pave ways for constructing antisintering gold nanocatalysts for industrial applications.
