Study Of Lower Olefins Synthesis Directly From Syngas On Fe-MnO_x Catalysts

The development of green processes through effective coal-transformation has a great significance on clean coal economics. Previous studies have demonstrated that the production of light olefins directly from coal-based syngas via the Fischer-Tropsch reaction (FTO) is a feasible route. This process can directly convert coal-based syngas to C2-C4 olefins straightforward, potentially reducing the cost of coal-to-olefins.In the present work, a series of Fe-MnO_x/SiO2 catalysts with different Fe/Mn ratios were prepared by incipient wetness impregnation. The performance of catalysts and the kinetics of the FTO reaction were measured using a fixed-bed micro-reactor. The texture property of catalysts was characterized by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The structure-modification during activation and the adsorption property of catalysts were studied with the Temperature-Programmed-Reduction (TPR) and Temperature-Programmed-Desorption (TPD). In combination with kinetics and characterization, the effect of MnO_x promoter on the FTO Fe-based catalysts was rationalized.The kinetic study showed that the activation energies with respect to paraffins and CO reaction orders with respect to all products were decreased simultaneously with the addition of MnO_x. Obviously, MnO_x could enhance the dispersion of FeOx and the surface basicity of Fe-based catalysts, thus facilitate the dissociative adsorption of CO and increasing CO conversion. MnO_x could also depress the re-adsorption and secondary reaction of light olefins, and enhance the formation rates of short chain olefins. Therefore, MnO_x plays an important role in promoting the reaction activity of Fe-based FTO catalysts and selectivity toward lower olefins.