Fe:Co/TiO2 bimetallic catalysts for the Fischer–Tropsch reaction: Part 3: The effect of Fe:Co ratio, mixing and loading on FT product selectivity Original Research Article

A series of catalysts, Fe:Co/TiO2, were made with different total metal loadings (Fe:Co wt.% loading; 1:1–5:5), with different Fe:Co ratios (at 10% metal loading) and using different synthetic procedures (impregnation versus physical mixing). The catalysts were characterised by BET, CO-chemisorption and Mössbauer spectroscopy. Their Fischer–Tropsch (FT) activity/selectivity properties were also measured. The co-impregnated catalysts revealed that the 5:5 Fe:Co catalyst showed higher activity than catalysts prepared with either 2.5:7:5 or 7.5:2.5 Fe:Co ratios. Physically mixed samples of Fe/TiO2 and Co/TiO2 showed different selectivities and also gave better FT activity than equivalent co-impregnated Fe:Co samples. The reducibility behaviour and Mössbauer spectra of the Fe:Co samples suggested that the catalyst activity and selectivity changes related to the Co phase, Fe–Co alloy formation and the ability of the Co to enhance the reducibility of the Fe. A relationship between reduction level and activity was observed. The bimetallic systems also showed good stability and only modest changes in selectivity with time on line.