NOx Storage and Reduction (NSR) Performance of Sr-Doped LaCoO3 Perovskite Prepared by Glycine-Assisted Solution Combustion

Abstract

Here, we successfully synthesized Sr-doped perovskite-type oxides of La1−xSrxCo1−λO3−δ, “LSX” (x = 0, 0.1, 0.3, 0.5, 0.7), using the glycine-assisted solution combustion method. The effect of strontium doping on the catalyst structure, NO to NO2 conversion, NOx adsorption and storage, and NOx reduction performance were investigated. The physicochemical properties of the catalysts were studied by XRD, SEM-EDS, N2 adsorption–desorption, FTIR, H2-TPR, O2-TPD, and XPS techniques. The NSR performance of LaCoO3 perovskite was improved after Sr doping. Specifically, the perovskite with 50% of Sr doping (LS5 sample) exhibited excellent NOx storage capacity within a wide temperature range (200–400 °C), and excellent stability after hydrothermal and sulfur poisoning. It also displayed the highest NOx adsorption–storage capacity (NAC: 1889 μmol/g; NSC: 1048 μmol/g) at 300 °C. This superior performance of the LS5 catalyst can be attributed to its superior reducibility, better NO oxidation capacity, increased surface Co2+ concentration, and, in particular, its generation of more oxygen vacancies. FTIR results further revealed that the LSX catalysts primarily store NOx through the “nitrate route”. During the lean–rich cycle tests, we observed an average NOx conversion rate of over 50% in the temperature range of 200–300 °C, with a maximum conversion rate of 61% achieved at 250 °C.