*2.1. Characterization*

Figure 1 shows X-ray diffraction (XRD) patterns of the materials after impregnation of La0.3Sr0.55 TiO3±<sup>δ</sup> (LST) and La0.3Sr0.55Ti0.95Ni0.05O3±<sup>δ</sup> (LSTN) with the metal precursors and subsequent calcination. XRD patterns are also given for LST (Figure 1a) and LSTN (Figure 1b). The reflections of the corresponding single metal oxides were observed in the XRD patterns of impregnated LST (LST-5Me, Me = Cr, Mn, Fe and Ni; Figure 1c), as well as impregnated LSTN (LSTN-5Me, Me = Cr, Mn and Fe; Figure 1d). Impregnation with the Mo precursor (LST-5Mo and LSTN-5Mo) resulted in the presence of reflections of a SrMoO4 phase, which is indicative of the segregation of small quantities of Sr from both LST and LSTN lattices during impregnation and calcination.

TPR experiments revealed the reduction of MnO, Cr2O3, Fe2O3 and NiO on LST up to 800 ◦C (Figure 2a). SrMoO4 was only partially reduced at these temperatures as is evident from the fact that H2 was still consumed at 800 ◦C. Similar behavior was also observed on impregnated LSTN materials (Figure 2c), on which also contributions of the LSTN support can be observed between ca. 450 ◦C and 650 ◦C. XRD measurements of the reduced materials confirmed the reduction of NiO, Fe2O3 and partial reduction of SrMoO4 on LST-5Ni, LST-5Fe and LST-5Mo, respectively (Figure 2b). No reflections of Cr and Mn metals were observed on reduced LST-5Cr and LST-5Mn, respectively. Instead, reflections of the single oxides were observed, similar to the calcined materials. This was likely due to the ex

situ nature of the XRD experiments and the strong tendency of dispersed Cr and Mn particles to form oxides.

**Figure 1.** Powder XRD patterns of (**a**) La0.3Sr0.55TiO3±<sup>δ</sup> (LST), (**b**) La0.3Sr0.55Ti0.95Ni0.05O3±<sup>δ</sup> (LSTN), (**c**) LST-5Me (Me = Mo, Mn, Cr, Fe, Ni) and (**d**) LSTN-5Me (Me = Mo, Mn, Cr and Fe). Markers indicate the presence of metal oxide phases after impregnation. Note that the intensity of the diffractograms in (**c**) and (**d**) is magnified (5×) with respect to (**a**) and (**b**).

All reflections were also encountered on the reduced LSTN-type materials. However, reduced LSTN-5Fe exhibited reflections that indicated the presence of two Fe allotropes (α-Fe and γ-Fe, Figure 2d), which is likely a consequence of Fe/Ni alloy formation during reduction at 800 ◦C as it was not observed on LST-5Fe. Subsequent rapid cooling to room temperature after reduction resulted in phase separation. This is supported by phase diagrams of the Fe-Ni system, which predict partial phase decomposition of the homogeneous γ-Fe/Ni alloy phase and various phase transformations during cooling [20]. Since cooling rates were high in these experiments (ca. 20 ◦C·min<sup>−</sup>1) the presence of metallic phases, which are not at equilibrium is highly probable [21]. Ni (111) reflections could be observed in LSTN, LSTN-5Cr and LSTN-5Mn, whereas the absence of the same in LSTN-5Fe and LSTN-5Mo can be regarded as an indication of Ni/Me alloy formation in the latter cases.

**Figure 2.** TPR profiles of (**a**) LST-5Me (Me = Mo, Mn, Cr, Fe, Ni) and (**c**) LSTN-5Me (Me = Mo, Mn, Cr, Fe). (**b**) Powder XRD patterns of reduced LST-type materials and (**d**) LSTN-type materials (10 vol.% H2/Ar, 800 ◦C, 1 h). The additional panel in (**d**) displays the magnified angular range 40◦ ≤ 2θ ≤ 48◦ (3×) with respect to intensity.
