Synthesis, characterization and catalytic activity of quadruple perovskite: CaCu3-xMnxTi4-xMnxO12 (x=0, 0.5 and 1.0)

Abstract

We report the low temperature synthesis of nanosized CaCu3-xMnxTi4-xMnxO12 (x= 0, 0.5 and 1.0) quadruple perovskites and their magnetic, dielectric and catalytic performance towards CO oxidation and methanol steam reforming (MSR). Our investigations reveal the pronounced effects of particle size and chemical substitution on all the physical properties reported here. The manganese doped samples exhibit remarkable change in magnetic properties, where antiferromagnetic pristine phase converted to ferrimagnetic phase for x=1. The dielectric constant values of the cold-pressed nanosized perovskites are ~103 and follows Maxwell-Wagner type relaxation. This value is about 100 fold lower than that of the bulk samples that has been ascribed to the effect of particle size and the absence of nano-twinning in the material as revealed from HRTEM studies. The doping of manganese further reduces the magnitude of dielectric value, which is the chemical effect. Mndoped samples show greater catalytic activity compared to the pristine sample towards CO oxidation due to a synergistic Cu-Mn interaction. The catalytic performance of these oxides for MSR reaction is intriguing. Although the catalyst undergoes decomposition in the MSR atmosphere causing a decrease in methanol conversion during time-on-stream (TOS) tests, the activity can be regenerated by in-situ or ex-situ annealing in air. The notable catalytic activity and reversibility between pristine and decomposed form are very interesting. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.