Mixture of α-Fe2O3 and MnO2 powders for direct conversion of syngas to light olefins

[Display omitted] •The mixture of MnO2 and α-Fe2O3 have been investigated in FTS.•The light olefins can reach up to 51.1 % on the MnO2/Fe2O3 = 1 catalyst.•The electronic state of iron atoms is affected by the existence of MnO2.•The interaction of Fe-Mn facilitates the formation of C-poor iron carbide (θ-Fe3C).•The θ-Fe3C is the effective active phase of forming light olefins from syngas. Although the direct conversion of syngas to light olefins (C2=-C4=) via Fischer-Tropsch synthesis (FTS) has made great progress, it remains a substantial challenge to elucidate the roles of iron carbides and promoters, due to the observed results are caused by numerous complexities and uncertainties. Herein, in order to better avoid the influence of diffusion rate, metal-inert support interaction, and reduce the effects of promoter on the coverage of active sites, a mixture of α-Fe2O3 and MnO2 powders catalyst was developed to understand the role of iron carbides in the formation of light olefins during the FTS. The characterization results confirmed that the interaction of Fe-Mn was formed on the surface of iron powder, and the electronic state of iron atoms was affected due to the existence of promoter MnO2 during carburization. Significantly, the results from in situ XPS and Mössbauer spectroscopy further evidence that promotion of the electron transfer from MnO2 to Fe2O3 facilitated the formation of C-poor θ-Fe3C, contributing to enrich the reactivity for the syngas to light olefins.