High-Surface-Area Synthesis of Iron-Doped CaTiO3 at Low Temperatures: New Insights into Oxygen Activation, Iron States, and the Impact on Methane Oxidation

In the present work, a series of CaTi1-xFexO3-delta (0 < x < 0.5) materials are prepared using a modified Pechini method based on citric acid and a polyol as chelating agents. The synthesis conditions are optimized with respect to the specific surface area and phase purity by varying polyols (ethylene glycol, glycerol, and 1.6-hexanediol) and the ratio between citric acid, polyols, and cations. The impact of the polyols and the iron content (up to 40 mol % on the B site) is studied with respect to the oxygen exchange rate, reducibility using H2- TPR, and catalytic performance for methane total oxidation. A correlation between the oxygen exchange rate studied using 18O exchange in powdered samples of CaTi1-xFexO3-delta (0 < x < 0.5) and ferric sites determined using Mo''ssbauer spectroscopy and H2-TPR is established. The oxygen activation and diffusion in CaTi1-xFexO3-delta (0 < x < 0.5) continuously increase in the studied range of Ti substitution. The methane oxidation performance does not increase above x = 0.3, showing that methane oxidation is not limited by surface oxygen activation and CH4 is activated by specific iron sites in Fe-doped perovskites.

Automated summary

In this study, a series of CaTi1-xFexO3-delta (0 < x < 0.5) materials were prepared using a modified Pechini method. The synthesis conditions were optimized to improve specific surface area and phase purity. The impact of polyols and iron content on the oxygen exchange rate, reducibility, and catalytic performance for methane total oxidation was investigated. The results showed that oxygen activation and diffusion in the materials increased with increasing Ti substitution. Additionally, the methane oxidation performance remained stable within a certain range and was activated by specific iron sites.