Hydrothermal preparation of Fe-Zr catalysts for the direct conversion of syngas to light olefins

Fe/Zr precursors were prepared by a one-step and two-step hydrothermal process respectively, following K promotion by incipient wetness impregnation, which then were used for the selective production of C-2-C-4 olefins via Fischer-Tropsch synthesis from syngas. The textural properties, phase structure, reduction behavior and the catalytic performance of the obtained catalyst samples were greatly affected by different preparation procedures. The T-Fe/Zr samples prepared by the two-step hydrothermal process caused a decrease in the surface area and easier reduction of iron species compared with that of the O-Fe/Zr samples prepared by the one-step hydrothermal process. The T-Fe/Zr samples before and after K promotion showed preferred orientation along the (-111) and (111) lattice planes of ZrO2 in contrast to the ZrO2 (101) lattice plane on O-Fe/Zr samples. For CO hydrogenation, all the catalysts exhibited high activity and good stability. The T-Fe/Zr-K catalysts with highly dispersed zirconia on the iron surface could prevent Fe-Zr mixed oxide formation by decreasing the interaction between iron and zirconia, leading to a slight increase in C-2-C-4 olefin selectivity and improvement on the product distribution.