Li-decorated Fe-Mn nanocatalyst for high-temperature Fischer-Tropsch synthesis of light olefins

Fe-Mn-Li nanocomposite particles were prepared using the combined urea hydrolysis and incipient wetness impregnation method. No surfactant or capping agents were involved in the preparation process, which ensured that this was low-cost and environmentally friendly method. In this study, the effects of urea hydrolysis temperature and Li amount on the catalyst structure, morphology, and particle size were analyzed combining various characterization techniques, including N-2 adsorption-desorption, X-ray diffraction (XRD), H-2 temperature-programmed reduction, CO2 temperature programmed desorption, CO temperature programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and Mossbauer spectroscopy. The nanocatalyst synthesized at 140 degrees C (Fe-Mn-140) presented the largest specific surface area and highest selectivity for light olefins and the lowest selectivity for CO2 and CH4 of all Fe-Mn-x samples in this study. These findings were consistent with the results of the Mossbauer spectroscopy and XRD testing, where Fe-Mn-140 was determined to contain the maximum amount of chi-Fe5C2 and minimum amount of Fe3O4 after reaction of all Fe-Mnx samples in this study. It was also determined that Li slightly restrained the reduction of iron oxides. In addition, Li increased the surface basicity of the catalysts, which reduced their selectivity for CH4 and light alkanes while increases those for light olefins and heavier hydrocarbons. Therefore, this study could lead to developing a facile and environmentally-friendly method for synthesizing iron-based nanocatalysts that present high activity and selectivity for light olefins for high-temperature Fischer-Tropsch synthesis processes.