Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis

The effects of Manganese(Mn)incorporation on a precipitated iron-based Fischer-Tropsch synthesis(FTS)catalyst were investigated using N_2 physical adsorption,air differential thermal analysis (DTA),H_2 temperature-programmed reduction(TPR),and M(?)ssbauer spectroscopy.The FTS perfor- mances of the catalysts were tested in a slurry phase reactor.The characterization results indicated that Mn increased the surface area of the catalyst,and improved the dispersion ofα-Fe_2O_3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction.The Fe-Mn inter- action also suppressed the reduction ofα-Fe_2O_3 to Fe_3O_4,stabilized the FeO phase,and(or)decreased the carburization degree of the catalysts in the H_2 and syngas reduction processes.In addition,incorporated Mn decreased the initial catalyst activity,but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe_3O_4,and improved further carburization of the catalysts.Manganese suppressed the formation of CH_4 and increased the selectivity to light olefins(C_(2-4)~=),but it had little effect on the selectivities to heavy(C_(5 )) hydrocarbons.All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter,to some extent,in the precipitated iron-manganese catalyst system.

Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis

The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N₂ physical adsorption, air differential thermal analysis (DTA), H₂ temperature-programmed reduction (TPR), and Mössbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of α-Fe₂O₃ and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of α-Fe₂O₃ to Fe₃O₄, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H₂ and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe₃O₄, and improved further carburization of the catalysts. Manganese suppressed the formation of CH₄ and increased the selectivity to light olefins (C⁼_2–4), but it had little effect on the selectivities to heavy (C₅₊) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.