**Appendix A**

Figure A1 shows the XPS spectra obtained for (a) BTCuO\_2, (b) BTCoO\_2, (c) BTFeO\_2, and (d) BTMnO\_2. Each figure contains the XPS spectra for the substituted metal (Cu2p3/2, Co2s, Fe2p3/2, Mn2p3/<sup>2</sup> transitions), oxygen (O1s transition), and barium (Ba3d5/<sup>2</sup> transition). In the spectra, the red lines represent the normalized peak and the blue lines represent the deconvolution of the normalized peaks.

**Figure A1.** XPS spectra obtained for (**a**) BTCuO\_2, (**b**) BTCoO\_2, (**c**) BTFeO\_2, and (**d**) BTMnO\_2.

The XPS spectra of the O1s transition show three contributions for all the catalysts that, according to literature [22,23], can be ascribed to: (i) lattice oxygen of metal oxides at ca. 529 eV; (ii) surface oxygen species such as oxygen peroxides (O2 <sup>2</sup><sup>−</sup>), surface carbonates (CO3 <sup>2</sup>−), and/or hydroxyl groups (OH−), at ca. 531 eV; and (iii) adsorbed water at ca. 533 eV.

The XPS spectra of the Ba3d5/<sup>2</sup> transition for all the catalysts show two contributions at approximately 778 eV and 780 eV binding energies. According to literature [24], they can be ascribed to: (i) Ba(II) oxide species (BaCuO2, BaTiO3-tet., Ba2TiO4), and (ii) BaCO3 respectively.

The assignment of the different contributions found in the XPS spectra of the substituted metal (Cu2p3/2, Co2s, Fe2p3/2, Mn2p3/2) transitions is shown in Table A1.



#### **References**


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