The stability of 10 wt% platinum supported on Si-doped alumina (Pt/Si-Al2O3) during the catalytic decomposition of energetic ionic liquid (or propellant) at 40 ° C was studied. The reaction was performed by successive injections of 79 wt% HAN (hydroxylammonium nitrate NH3OHNO3) aqueous solution onto the catalysts in a constant volume batch reactor. The four studied catalysts remain active with a fast reaction rate (up to 450 mbar s(-1)), even in the presence of an excess of residual aqueous solution. For all catalysts, the structural studies reveal the presence of theta alumina associated with silica and platinum particles. After the propellant decomposition, alteration in metallic particle size is observed as is the formation of nanosized platinum agglomerates in the reaction medium, which are probably responsible for the excellent catalytic activity. A model is suggested, explaining the part played by platinum and silica particles at the surface of the materials during the propellant decomposition reaction. © 2005 Elsevier Inc. All rights reserved.