Effect of manganese on a potassium-promoted iron-based Fischer-Tropsch synthesis catalyst

Abstract

The effects of manganese promoter on the reduction-carburization behavior, surface basicity, bulk phase structure and their correlation with Fischer-Tropsch synthesis (FTS) performances have been emphatically studied over a series of spray-dried Fe-Mn-K catalysts with a wide range of Mn incorporation amount. The catalysts were characterized by means of H 2 and CO temperature-programmed reduction (TPR), CO 2 temperature-programmed desorption (TPD), Mo¨ssbauer spectroscopy etc.. The results indicated that small amount of Mn promoter can promote the reduction of the catalyst in H 2 . However, FeO phase formed during reduction is stabilized by MnO phase with the further increase of Mn content, making FeO phase difficult to be reduced in H 2 . The addition of Mn promoter can stabilize the Fe 2+ and Fe 3+ ions, and suppresses the reduction and carburization of the catalyst in syngas and CO. Mn promoter can also enhance the amount of the basic sites and weaken the strength of the basic sites, which possibly come from the reason that the Mn-K interaction is strengthened with the addition of Mn promoter. The change of surface basicity can modify the selectivity of hydrocarbons and olefins, and the change of bulk structure phase derived from the addition of Mn promoter will affect the catalyst activity and run stability. The synergetic effects of the two main factors result in an optimized amount of Mn promoter for the highest catalyst activity and heavy hydrocarbon selectivity in slurry FTS reaction of Fe-Mn-K catalysts.

Comparison of FeMn, FeMnNa and FeMnK Catalysts for the Preparation of Light Olefins from Syngas

“…But compared with FeMnNa and FeMnK, it can also be observed that the presence of potassium and sodium promoters cause the reduction peaks to shift to higher temperatures. The former does not strongly affect the reduction behavior of the catalyst, but the latter strongly suppresses the reduction of catalyst, implying that there are some interactions between Na and K promoters with manganese oxides and iron oxides, 17 promoting the aggregation of α-Fe2O3 crystallite, which is consistent with the observed decrease of the specific BET surface area. Beyond this, as shown by the results of XPS, the high enrichments of Mn, Na, and K promoters on the catalyst surface reduce the surface concentration of active Fe and result in a decrease in H2 adsorption, which suppresses the reducibility of iron oxide around the Na and K promoters.…”

“…Similar results have also been found by other investigators. 16,17 The results of XPS show the surface compositions of the catalyst calculated from the analysis of these spectra. As shown in Table 2, it is found that the Mn/Fe, Na/K, and K/Fe atomic ratios on the surface are much larger than that in the bulk of the samples due to the enrichment of promoters on the surface of the catalysts.…”

“…The disappearance of diffraction peaks for the manganese phase is probably due to the dissolving of Mn atoms in the hematite phase. 17,22…”

Rapidly Quenched Skeletal Fe-Based Catalysts for Fischer−Tropsch Synthesis

“…The changes in peak positions are consistent with the consensus that K and Mn can influence the interaction of CO on Fe as electronic promoters. [28][29][30][31] Moreover, Figure 3 implies that Mn and K tend to occupy the more open Fe(111) surface on R-Fe crystallites, which weakens the high-temperature desorption peak.…”

Synthesis of Hydrocarbons from H2‐Deficient Syngas in Fischer‐Tropsch Synthesis over Co‐Based Catalyst Coupled with Fe‐Based Catalyst as Water‐Gas Shift Reaction

“…By contrast, Qing et al have reported that in the H 2 -TPR profiles a first peak of a calcined composite of Fe and Zr without SiO 2 appeared at higher temperature than that of hematite due to the cover of Fe sites with enriched Zr [34]. The addition of Mn or Ce species to Fe-based catalysts causes the interaction between the Fe species and the metal species, leading to the delay of the reduction of the Fe species [20,[35][36][37]. According to the findings reported above, it is suggested that in the metaladded Fe-based catalysts the reduction of the Fe species was suppressed to shift the first peak to higher temperature in the H 2 -TPR profile due to the interaction of the Fe species and the metal species resulting from the addition of the large amount of the metal species although the Fe species were highly dispersed.…”