Chemical structures of coprecipitated Fe-Ce mixed oxides

Two series of Fe-Ce catalysts were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and physical mixing of pure Fe and Ce precursors. Evidence of the presence of a chemical interaction between Fe and Cc was found in the calcined state of the coprecipitated catalysts. Such evidence was obtained with different techniques. The Fe-Ce interaction occurs through the formation of hematite-like and cubic ceria-like solid solutions. In the hematite-like solid solution, Ce cations are dissolved in the hematite structure, whereas in the cubic ceria-like solid solution Fe cations are dissolved in the ceria structure. Such interactions were absent in the samples prepared by the physical mixing. It is suggested that the Fe-Ce interaction present in the calcined state results in a strong Fe-Ce interaction in the final catalyst that defines their better catalytic properties. When tested in the Fischer-Tropsch synthesis of hydrocarbons from CO + H-2 gas mixtures, the coprecipitation method series showed higher CO conversion rates, higher hydrocarbon formation rates, and a higher degree of olefinicity than the pure Fe catalyst sample and the Fe-Ce samples prepared by physical mixing.