The Application of Moessbauer Emission Spectroscopy to Industrial Cobalt Based Fischer―Tropsch Catalysts

摘要

The application of Moessbauer emission spectroscopy to study cobalt based Fischer―Tropsch catalysts for the gas-to-liquids process was investigated. It was shown that Moessbauer emission spectroscopy could be used to study the oxidation of cobalt as a deactivation mechanism of high loading cobalt based Fischer―Tropsch catalysts. Oxidation was observed under conditions that are in contradiction with the bulk cobalt phase thermodynamics. This can be explained by oxidation of small cobalt crystallites or by surface oxidation. The formation of re-reducible Co~(3+) species was observed as well as the formation of irreducible Co~(3+) and Co~(2+) species that interact strongly with the alumina support. The formation of the different cobalt species depends on the oxidation conditions. Iron was used as a probe nuclide to investigate the cobalt catalyst preparation procedure. A high-pressure Mossbauer emission spectroscopy cell was designed and constructed, which creates the opportunity to study cobalt based Fischer-Tropsch catalysts under realistic synthesis conditions.