Surface sensitive catalytic mechanism of morphology and facet controlled α-MnO2 nanostructures in the decomposition of ammonium perchlorate

Abstract

The catalytic properties of nanostructured materials are significantly influenced by their specific crystallographic facets. Each facet presents unique atomic configurations and electronic structures, which play a crucial role in bond activation, reactant adsorption, and the stabilization of intermediates. This study investigated the influence of distinct α-MnO₂ nanostructures on the thermal decomposition of ammonium perchlorate (AP), an important oxidizer in solid propellants. MnO₂ nanorods (1D) and nanocubes (3D) were synthesized and their catalytic activities were assessed. Nanocubes, featuring a microporous structure and predominantly exposing the (211) crystallographic facet, demonstrated enhanced catalytic efficiency in the decomposition of AP compared to nanorods primarily exposing the (310) facet. XPS analysis confirmed the presence of Mn⁴⁺/Mn³⁺ redox couples and surface oxygen vacancies, which collectively facilitated electron transfer to the perchlorate anion (ClO₄⁻), thereby promoting its reduction and accelerating one of the kinetically competing decomposition reactions. This resulted in a significant enhancement in NO₂ evolution relative to N₂O, during the decomposition reaction, suggesting a catalyst induced alteration in the decomposition pathway.