Exsolution of Fe–Ni alloy nanoparticles from (La,Sr)(Cr,Fe,Ni)O3 perovskites as potential oxygen transport membrane catalysts for methane reforming

Abstract

(La_0.75Sr_0.25)(Cr_0.5Fe_0.5−xNi_x)O₃ perovskites were investigated as potential catalysts for oxygen transport membranes for methane reforming applications. XRD was performed to study the structural changes that took place when Fe was partially substituted by Ni, in both oxidising and reducing environments. TGA measurements demonstrated that the oxygen deficiency of these perovskites under reducing conditions was enhanced by increasing the level of Ni doping, due to the reduction of the Fe³⁺/Fe⁴⁺ and Ni²⁺ species to lower cation valences. SEM and TEM-EDX analyses showed that upon reduction exsolution of bimetallic Fe–Ni alloy nanoparticles took place on the surface of the perovskite, which was beneficial for the catalyst's activity. The optimum stoichiometry was the (La_0.75Sr_0.25)(Cr_0.5Fe_0.35Ni_0.15)O₃ perovskite, which during catalytic testing, demonstrated 72% CH₄ conversion, which was 20 times higher than that of the initial perovskite.