Modified surface and bulk properties of Fe-substituted lanthanum titanates enhances catalytic activity for CO + N 2O reaction

Abstract

Iron substituted lanthanum titanates with nominal composition La 2Ti 2(1− x) Fe 2 x O 7− δ (0.0 ≤ x ≤ 1.0) samples, were synthesized by gel combustion and conventional solid state reaction. The samples have been characterized by XRD, N 2-BET, SEM, FTIR, Mössbauer spectroscopy and TPR. Catalytic activity of these samples was evaluated for a decomposition reaction of N 2O using CO. Transition from La 2Ti 2O 7 (layered perovskite, A 2B 2O 7) to single phase, LaFeO 3 (perovskite, ABO 3) 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 (ABO 3) 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 N 2O 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 T max observed in their TPR profiles and enhanced activity for CO + N 2O reaction as compared to pristine samples.