Mn- or Cu- substituted LaFeO3-based three-way catalysts: Highlighting different catalytically operating modes of La0.67Fe0.8M0.2O3 (M=Cu, Mn)

[Display omitted] •The structure and surface composition of Cu- and Mn-doped La0.7FeO3 was refined using both bulk and surface characterization techniques•The CuO segregated phase plays the role of redox-active center in Cu-LaFeO3 material.•Mn3+ cations embedded at B-site of the perovskite lattice are the major redox-active centers in Mn-doped La0.7FeO3. The present work aims at presenting our investigations on the redox behaviour of Cu- or Mn-doped LaFeO3-based perovskite powders under three-way catalysis (TWC) relevant conditions. Two distinct La-deficient catalysts of generic formula La0.67Fe0.8Mn0.2O3 and La0.67Fe0.8Cu0.2O3 denoted as Mn-dLFO and Cu-dLFO, respectively, were prepared based on the conventional citrate complexation route and systematically investigated using complementary characterisation techniques. This study has made it possible to highlight fundamentally different structures. In Cu-dLFO, most Cu2+ cations are expelled from the LaFeO3 perovskite lattice in the form of a segregated CuO phase. On the other hand, in the case of Mn-dLFO, majority of Mn3+ cations are stabilised within the perovskite solid solution, while substantial iron exsolution in the form of an additional α-Fe2O3 phase was evidenced. The evolution of both catalysts during CO-TPR using operando Raman revealed the formation of polycyclic aromatic hydrocarbons (PAHs) besides the relative structural stability of the LaFeO3 lattice. The reduction of Mn3+ to Mn2+, indirectly suggested by Raman analysis, is further supported by a quasi-in situ XPS study. The latter also evidenced the reduction of CuO to metal copper to a large extent in Cu-dLFO. In addition, a share of the α-Fe2O3 phase present in Mn-dLFO is reduced to metal Fe0 during CO oxidation, and is fully re-oxidised upon NO reduction. Our investigation thus evidences that both copper and manganese sites in Cu-dLFO and Mn-dLFO, respectively, are redox-active centres upon CO oxidation/NO reduction with, however, varying operating modes underpinned by their fundamentally different structures.