Insights into the Electronic Effects of the Zn Promoter\non Co<sub>2</sub>C Nanoprisms for Fischer-Trospch to Olefin Reaction

Co<sub>2</sub>C nanoprisms were developed for the Fischer–Tropsch\nto olefins (FTO) reaction a few years ago, while to the best of our\nknowledge, the study of the electronic promoters were hardly reported\ndue to the instability of the Co<sub>2</sub>C nanostructures with\npromoters. The absence of the promoters limited the performance modulation\nand industrial application of the Co<sub>2</sub>C-based FTO catalysts.\nThe work reported here was aimed at developing a new strategy to synthesize\nthe Zn-promoted Co<sub>2</sub>C nanoprisms and understanding the electronic\neffects of the Zn promoters on the Co<sub>2</sub>C facets without\nconfusion over the geometric effects. Detailed characterizations of\nthe carbonized and spent samples suggested that the Zn promoters lowered\nthe stability of the Co<sub>2</sub>C nanostructures and led to the\nformation of the surface Co<sup>0</sup> species in the spent samples\nwith high Zn contents, which was responsible for the decrease of the\nO/P ratios and the increase of the CH<sub>4</sub> selectivity. The\nXPS results showed that the electrons transferring from the Zn promoters\nto the Co<sub>2</sub>C facets enriched the density of the electron\nclouds of the Co species on the Co<sub>2</sub>C facets. Further evidence\nfor the enhanced CO adsorption and dissociation routes were obtained\nfrom the measurements of the CO temperature-programmed desorption.\nThe Zn promoters increased the strong adsorption sites, which were\nnot active for the Boudouard reaction and the increase of the CO<sub>2</sub> selectivity originated from the Water–Gas Shift reaction.\nThe activation route of the adsorbed CO species on the strong adsorption\nsites was H-assisted dissociation rather than direct dissociation,\nresulting in the inhibition of the carbene-mediated routes and the\nshifting of product selectivity toward light hydrocarbons.