This work addresses the microstructure of perovskites LaBO₃ (B = Fe, Co, Ni) and the application of the perovskites ABO₃ (A = La, Ca, Sr, and B = Fe, Co, Ni) in ammonia (NH₃) decomposition.

Bulk analysis by diffraction experiments and local structure analysis by total scattering methods with subsequent pair distribution function analysis was performed. Conducting these experiments with neutron and synchrotron radiation resulted in gaining highly detailed insights into the microstructure. While LaFeO₃ did not show any deviation from its ideal crystal structure, there were noticeable deviations from the ideal crystal structure for LaCoO₃. Despite the complementary effect of all methods applied, these could not be identified. In LaNiO₃, Ruddlesden-Popper-type faults could be observed. A crystallographic model containing these stacking faults was set up and applied in Rietveld refinements to estimate the amount of stacking faults in LaNiO₃. The gradual increase of the distortion of the ideal crystal structure from Fe via Co to Ni can be accounted for by the individual electronic properties of these transition metals.

The in situ formation of NH₃ decomposition catalysts derived from perovskites ABO₃ (A = La, Ca, Sr, and B = Fe, Co, Ni) via operando X-ray diffraction experiments was studied in a gas flow cell setup at synchrotron beamlines. This way, the reduction behavior and the formation of intermediate phases during the activation depending on the composition of the perovskite precatalyst was studied. Complementary NH₃ conversion measurements in a plug flow cell with a gas flow of 100 % NH₃ were conducted to determine the catalytic performances. Moreover, temperature programmed reduction experiments of the perovskites were performed to evaluate their reducibility. Furthermore, electron microscopy images of the activated samples after catalysis were collected in order to analyze their crystallite size and particle morphology. The analyses have consistently shown that LaFeO₃ does not decompose under NH₃ and is inactive as a catalyst. In contrast, Co-Ni-based perovskites completely reduce to metallic Co/Ni on a La₂O₃ support. The higher the reducibility of a perovskite, the less distinctive intermediate phases form during that process. Partially substituting La³⁺ by Sr²⁺ in the LaCoO₃ perovskite structure has resulted in the highest measured NH₃ decomposition conversion rate in this study.