Modified surface and bulk properties of Fe-substituted lanthanum titanates enhances catalytic activity for CO + N2O reaction

Iron substituted lanthanum titanates with nominal composition La2Ti2(1−x)Fe2xO7−δ (0.0 ≤ x ≤ 1.0) samples, were synthesized by gel combustion and conventional solid state reaction. The samples have been characterized by XRD, N2-BET, SEM, FTIR, Mössbauer spectroscopy and TPR. Catalytic activity of these samples was evaluated for a decomposition reaction of N2O using CO. Transition from La2Ti2O7 (layered perovskite, A2B2O7) to single phase, LaFeO3 (perovskite, ABO3) was observed for the samples having ≥40–60% Fe content. The microstructural analysis by SEM revealed homogeneous elongated shaped rods on single phased LTOGC surface, attributed to the layered perovskite whereas spherical grains are due to single perovskite (ABO3) phase present in LF(0.4)GC samples. Mixed phased samples showed both elongated and spherical shape particles as observed in the SEM images. Among all samples, LF(0.6)GC have shown maximum activity of 100% conversion at 395 °C for decomposition of N2O using CO and at 325 °C for CO oxidation. The substitution-induced anionic vacancies and asymmetric environment around Fe as suggested by Mössbauer results in partially substituted, LF(0.4)GC/SS and LF(0.6)GC/SS are responsible for considerable lowering in Tmax observed in their TPR profiles and enhanced activity for CO + N2O reaction as compared to pristine samples.

Figure optionsDownload high-quality image (148 K)Download as PowerPoint slideResearch highlights▶ Nominal compositions La2Ti2(1−x)Fe2xO7−δ by gel combustion, solid state route. ▶ Transition from La2Ti2O7 to LaFeO3 single phase beyond 40–60% Fe content. ▶ Maximum activity over LF(0.6)GC for decomposition of N2O using CO. ▶ Substitution-induced anionic vacancies, asymmetric environment around Fe. ▶ Surface–bulk-activity correlations.