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

• Published in: Applied catalysis. B, Environmental Environmental, 2019-12, Vol.259, p.118052, Article 118052
• Main Authors: Onrubia-Calvo, Jon A., Pereda-Ayo, Beñat, Bermejo-López, Alejandro, Caravaca, Angel, Vernoux, Philippe, González-Velasco, Juan R.
• Format: Article
• Language: English
• Subjects: Adsorption; Air pollution control; Alumina-supported; Aluminum oxide; Barium oxides; Catalysts; Chemical Sciences; Doping; Electron microscopy; Formulations; Impregnation; Incorporation; Moisture content; Nitrogen dioxide; Nitrogen oxides; NOx storage and reduction; Oxidation; Palladium; Pd-doped; Pd-impregnated; Perovskite; Perovskites; Photoelectrons; Reduction; Regeneration; Storage; Strong interactions (field theory); Surface chemistry; X-ray diffraction
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.118052

Evolution of NOx storage capacity (NSC), NOx global conversion and nitrogen yield (YN2) values with palladium content at 350 °C; where Pd was incorporated by impregnation over supported perovskite (Pd-impregnated) or by doping perovskite structure (Pd-doped). [Display omitted] •Pd incorporation by impregnation or doping 30% La0.7Sr0.3CoO3/Al2O3 is analysed.•Wetness impregnation is the optimum Pd incorporation method.•Maximum NOx removal efficiency is related to Pd-perovskite interactions.•1.5% Pd-30% La0.7Sr0.3CoO3/Al2O3 shows maximum N2 yield of 69.5%.•NSR performance is even above the shown by 1.5% Pt-15% BaO/Al2O3 model catalyst. Here we report the effects of the incorporation of palladium into 30% La0.7Sr0.3CoO3/Al2O3 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% La0.7Sr0.3Co1-yPdyO3/Al2O3) or by wetness impregnation over alumina-supported perovskite (y% Pd-30% La0.7Sr0.3CoO3/Al2O3). The results of X-Ray diffraction, N2 adsorption-desorption at −196 °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 N2 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 NOx removal efficiency and minimum