Metal oxide nanoparticles have been used as burning rate catalysts for ammonium perchlorate (AP) decomposition in composite solid propellants. Though most papers point to the efficiency of different sizes, shapes and compositions, the texture of the agglomerated particles plays an important role in the catalytic efficiency, but this aspect is not always discussed. In this paper, iron oxide and composite iron oxide/silica powders were synthesized in microemulsion systems and their effect on the decomposition of AP was investigated. X-ray diffraction (XRD) analysis and Fourier transformed infrared spectroscopy (FT-IR) showed that the synthesized powders have an amorphous to nanocrystalline pattern, with Fe2O3 composition. The use of different FT-IR spectroscopic techniques - transmission, diffuse reflectance (DRIFT) and universal attenuated total reflectance (UATR) - allied to electron microscopy analysis allowed the characterization of the samples' surface, indicating that silicon oxide forms a thick matrix that covers the iron oxide nanoparticles. Adsorption of N-2, light scattering and electron microscopy pointed that all samples are formed by mesoporous agglomerated nanoparticles containing micropores indicating that silicon oxide forms a thick matrix that covers the iron oxide nanoparticles. Adsorption of N-2, pointed that all samples show different microstructures and light scattering indicated results refer to agglomerated particles. Finally, the catalytic effect of the samples on the decomposition of AP was evaluated by thermogravimetric analysis coupled to differential thermal analysis (TG/DTA), showing that only the high temperature decomposition step of AP was affected by the catalyst, shifting to lower temperatures the higher the surface area of the synthesized iron oxide sample, regardless of the presence of the silica matrix.