In situ investigation of iron-based ammonia decomposition catalysts derived from crystalline precursors

• Applicants: Professor Dr. Malte Behrens, since 10/2021; Professorin Dr. Claudia Weidenthaler
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Technical Chemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 442614184

Ammonia as a carbon-free hydrogen storage molecule has received considerably low attention as a potential energy carrier in the future. Although many findings for the ammonia decomposition could be obtained from the well-studied ammonia synthesis reaction, dedicated research is still necessary due to significant differences in process conditions. The most active catalysts for the decomposition reaction are based on ruthenium. Highly available non-noble metals are an attractive alternative that has not been studied at the same level of detail. In this project, supported iron catalysts are synthesized in the presence of nickel and cobalt as promotors. Together with magnesium or aluminum as constituent elements of the support materials, crystalline hydroxide or hydroxy carbonate precursors with a layered structure are obtained by means of pH-controlled co-precipitation. In addition to conventional aqueous synthesis, a microemulsion-based approach is implemented to modify the meso- and nanostructure of the precursors. After calcination, activation takes place in ammonia, either with or without a reduction step beforehand. By modifying the precursor properties, both the chemical composition and the structure of the resulting catalyst can be explicitly influenced, allowing a systematic investigation of the structural sensitivity of this reaction. For this purpose, catalytic tests are carried out in pure ammonia and to some extent in dilute gas to address the influence of the chemical potential on the activity and stability. For structure-activity correlations, changes in microstructure, local structure, and phase composition are monitored by X-ray diffraction, pair distribution functions, and X-ray absorption spectroscopy under in situ conditions to gain a deeper understanding of the catalytically active state.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Klaus Friedel Ortega, until 9/2021