Fischer-Tropsch Synthesis. Reduction Behavior and Catalytic Activity of Fe-Ce Systems

摘要

Several Fe-Ce catalysts for FT synthesis were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and a physical mixture of pure Fe and Ce precursors. The iron phases present in the activated catalysts were identified by XRD and M?ssbauer spectroscopy. A good correlation between both techniques was found. The results revealed that the cerium oxide in the samples prepared by coprecipitation produces two effects: (i), stabilization of metastable species (Fe1–xO), and (ii), a decrease in the crystallite size of the iron species upon increasing Ce-contents, as inferred from an increase in superparamagnetic species. The catalysts were tested in CO hydrogenation in a flow reactor. It was found that selectivity towards light olefins increases for the coprecipitated Ce-containing catalysts, whereas CO conversion followed the opposite trend. Since the Fe1–xO phase was detected in these catalysts, it is suggested that the formation of the Fe1–xO phase would be responsible for the drop in catalytic activity.