Three different types of perovskite-based nanocomposites were synthesized by calcination of the same gel mixtures (molar ratio of 0.4 La : 0.6 Sr : 1.0 Co) at different reaction conditions (unconventional method: calcination at 1000 o C and 800 o C under vacuum and conventional method:calcination in air at 1000 o C). The obtained products were studied by multi-analytic techniques including Powder X-ray Diffraction (PXRD), High-Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive X-ray spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS). NO x reduction using propene (C 3 H 6 ) as a reductant in the presence of oxygen was studied by Temperature Programmed Surface Reaction (TPSR). The analyzed results showed that multi-phase products are found by the unconventional method (in the absence of oxygen) while the conventional method (in the presence of oxygen) yields single-phase perovskites. The multi-phase nanocomposite products prepared under vacuum at 1000 o C exhibit higher catalytic activity and higher N 2 yield compared to the samples obtained under vacuum at lower temperature (800 o C) and the single-phase perovskites.