Abstract
A systematic study was undertaken to investigate the effects of Al 2O 3/SiO 2 ratio on reduction, carburization and catalytic behavior of iron-based Fischer–Tropsch synthesis (FTS) catalysts promoted with potassium and copper. The catalysts were characterized by N 2 physical adsorption, CO 2 temperature-programmed desorption (TPD), H 2 temperature-programmed reduction (TPR) and Mössbauer effect spectroscopy (MES). CO 2-TPD indicated that Al 2O 3 binder has stronger acidity than SiO 2 binder and weakens the surface basicity of the catalysts. H 2-TPR profiles suggested that the lower Al 2O 3/SiO 2 ratio promotes the reduction of Fe 2O 3→Fe 3O 4. With further increasing Al 2O 3/SiO 2 ratio, the transformation of Fe 2O 3→Fe 3O 4 shifts to higher temperatures. The MES results showed that the increase of Al 2O 3/SiO 2 ratio leads to the relatively large crystallite size of α-Fe 2O 3 and inhibits carburization of the catalyst. During reaction tests in a fixed bed reactor it was found that a maximum in catalyst activity is noted at the Al 2O 3/SiO 2 ratio of 5/20 (weight basis). The selectivity to olefins shows a rapid decrease and the formations of methane and light hydrocarbons are promoted with increasing Al 2O 3/SiO 2 ratio. The oxygenate selectivity in total products increases with increasing Al 2O 3/SiO 2 ratio.
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