Ammonia decomposition and synthesis over multinary magnesioferrites : promotional effect of Ga on Fe catalysts for the decomposition reaction
| Autor: | Fatih Özcan, Christian Lüttmann, Denise Rein, Jan Folke, Markus Heidelmann, Kevin Kähler, Klaus Friedel Ortega, Justus Heese, Malte Behrens, Robert Schlögl |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
Chemistry
Organic Chemistry Inorganic chemistry Chemie 02 engineering and technology engineering.material 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Decomposition Catalysis 0104 chemical sciences law.invention Inorganic Chemistry Magnesioferrite Ammonia production Physisorption law engineering Calcination Physical and Theoretical Chemistry 0210 nano-technology Ternary operation Chemical decomposition |
| Popis: | MgFe2O4-derived Mesoporous spinels of the type MgFeM3+O4 with M3+=Fe,Al, and Ga obtained upon calcination of hydrotalcite-like compounds were investigated in the ammonia decomposition reaction at 1atm and the synthesis of ammonia at 90bar. The corresponding precursors were synthesized by co-precipitation at 50°C and constant pH of 10.5. N2 physisorption, PXRD, TEM, TPR, and TPD were applied in order to obtain information about the textural, (micro-)structural, solid-state kinetic, and adsorption properties. While phase-pure LDHs were obtained for Al and Ga, magnesioferrite as the desired oxide phase and a low fraction of magnetite were formed besides the targeted precursor phase during co-precipitation in the presence of Fe2+ and Fe3+ species. Reduction of the binary and ternary magnesioferrites occurs via two consecutive reactions. Only the second stage is shifted towards higher temperatures after incorporation of Al and Ga. The latter element boosts the catalytic decomposition of ammonia, yielding a 2-fold and 5-fold higher conversion at 500°C compared to the samples containing Fe3+ and Al3+ species, respectively. In situ XRD measurements showed that this unprecedented promotional effect is related to the generation of (Fe, Ga)Fe3N. This phase, however, is detrimental for the synthesis of ammonia at elevated pressures in which the binary system outperforms the ternary spinels, yielding 30% of the activity obtained with a highly promoted Fe-based industrial catalyst. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|