Pd-doped or Pd impregnated 30% La0.7Sr0.3CoO3/Al2O3 catalysts for NOx storage and reduction

Here we report the effects of the incorporation of palladium into 30% La0.7Sr0.3CoO3/Al2O catalyst by different methods on the NOx storage and reduction behaviour. Several catalysts were prepared incorporating four palladium nominal loadings (0.75, 1.5, 2.25 and 3.0%) by doping the perovskite formulation (30% La0.7Sr0.3CoO3/Al2O) or by wetness impregnation over alumina-supported perovskite (y% Pd-30% La0.7Sr0.3CoO3/Al2O). The results of X-Ray diffraction, N-2 adsorption-desorption at -196 degrees C, electron microscopy, temperature programmed techniques, Raman and X-ray photoelectron spectroscopies demonstrated that the wetness impregnation method induces the formation of small PdO particles homogenously distributed over the surface in strong interaction with the perovskite. Meanwhile, doping method leads to the formation of a mix between intraframework palladium species and surface agglomerated PdOx particles with weaker interaction with the perovskite phase. Therefore, palladium accessibility and the synergetic effects with the perovskite are lower for Pd-doped samples. The NO-to-NO2 conversion is similar irrespective of the palladium content and the incorporation method. This confirms the perovskite phase as the main active site for NO oxidation. However, NOx adsorption during lean conditions and NOx reduction to N-2 during rich periods are significantly promoted after the incorporation of palladium, especially by impregnation method. This enhancement is assigned to better NOx adsorption sites regeneration and to a promotion of NOx reduction rate, respectively. Thus, the best De-NOx performance of Pd-impregnated catalysts is derived from the higher efficient use of the palladium active sites. Among the developed formulations, the 1.5% Pd-30% LSCO/Al2O3 sample shows the best balance between NO. removal efficiency and minimum palladium content. This sample shows a NO removal efficiency and nitrogen yield as high as 86.2% and 69.5%, respectively. Based on these results, the developed formulation is revealed as a promising alternative to the NSR model catalyst (1.5% Pt-15% BaO/Al2O3) for NOx removal in the automotive application.