Indium as a chemical promoter in Fe-based Fischer-Tropsch synthesis Original Research Article

The ability of indium to act as a chemical promoter in Fe-based FTS reaction was evaluated and compared to that of copper. Indium was chosen for study due its relationship to Cu through the ‘Knightʹs Move’ relationship. N2 physisorption, temperature programmed reduction (TPR), X-ray diffraction (XRD) and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) were employed to characterise the catalysts. “In situ” Fischer-Tropsch synthesis (FTS) reactions were also performed in a DRIFTS reactor. It was found via TPR studies that indium exhibited a similar ability to reduce Fe as found for copper. Results obtained from XRD and N2 physisorption experiments showed indium promoted catalysts give comparable results to those of copper promoted catalysts. However, indium decreased the % reducibility and CO adsorption ability of the Fe catalyst. Indium also lowered the FTS activity of the Fe-based catalyst, an effect ascribed to be associated with the low melting point of In. The effect of adding indium to a multi-promoted Fe-based FTS catalyst was also investigated. The addition of indium suppressed the reduction properties of the catalyst when H2 was employed as a reductant. When CO was employed as a reductant, the reduction/carburization properties were improved and resulted in a selectivity shift to heavy weight hydrocarbons during the FTS reaction. Adding indium to the multi-promoted catalyst also lowered the catalyst surface area which resulted in a decrease to the FTS activity. It appears that while the ‘Knightʹs Move’ relationship is consistent with Cu and In both acting to enhance Fe reduction, the low In melting point determines the poor activity of the FT catalysts.