| Popis: |
The behavior of Fe based catalysts supported on ZrO2, SiO2, γ‐Al2O3, CeO2 and TiO2 during calcination, reduction and FT synthesis have been studied via in situ Mossbauer spectroscopy. It was found that the type of metal support interaction i.e. surface migration or bulk diffusion during calcination was dependant on the type of support used. Surface migration of Fe3+ during calcination was dominant for ZrO2, CeO2 and γ‐Al2O3 and this resulted in the sintering of α‐Fe2O3 crystallites. Whereas bulk diffusion was observed mainly for the catalysts prepared using SiO2 and TiO2, causing a stabilization of the small crystallites of Fe3+ that interacted strongly with the support. Upon reduction, the large crystallites of α‐Fe2O3 were found to reduce readily compared to the small crystallites of Fe3+, except for the catalyst prepared using γ‐Al2O3, as a support, where the presence of Al3+ resulted in the formation of spinel like species with the formula (Fe2−x3+Alx3+Fe2+)O4 which are resistant to reduction. Upon ex... |
