Unusual Effect of Support Carbonization on the Structure and Performance of Fe/Mgal₂o₄ Fischer–Tropsch Catalyst

Abstract

Carbonization of MgAl2O4 spinel via glucose treatment is applied for preparation of spinel‐supported iron Fischer–Tropsch synthesis (FTS) catalysts. The catalysts are characterized by low‐temperature adsorption of N2, transmission electron microscopy (TEM), Mössbauer spectroscopy, in situ magnitometry, and are tested in high‐temperature FTS conditions. Surface carbonization leads to magnetite formation in the course of catalyst calcining, likely due to reductive function of surface carbon. In contrast, hematite is formed if iron precursor is deposited on pristine spinel. Support carbonization facilitates iron precursor reduction into carbide during catalyst activation step in synthesis gas flow and gives rise to highly dispersed iron nanopartilcles. Comparison of sequential and co‐impregnation approaches for support carbonization reveal that the first is preferable in terms of Hägg carbide formation during catalyst activation. Specific activity of the catalysts in high‐temperature FTS is approximately doubled due to the support carbonization. The carbonization also boosts C5+ selectivity and olefin percentage in the product hydrocarbons, while methane formation is suppressed. Adding potassium to catalyst formulation suppresses iron carbide oxidation and Fe3O4 formation, and promotes conversion of χ‐Fe5C2 into θ‐Fe7C3 in FTS conditions.

Functionalized Magnetite Nanoparticles: Characterization, Bioeffects, and Role of Reactive Oxygen Species in Unicellular and Enzymatic Systems

“…The composition and morphological properties of MNPs were studied by Mössbauer spectroscopy, and related spectra, along with their description and results of simulation in different state superparamagnetic relaxation models are presented in Table 1 and Supplementary materials (Figure S1, Table S1) . Relying on the presented results, it can be argued that magnitudes of magnetic splittings, obtained even for spectra at low temperatures, are lower than expected for massive samples of magnetite and maghemite [ 81 ], which is typical for nanosized materials [ 82 ]. Indeed, the sizes of magnetic domains can be estimated in the range from 12.6 (for Fe 3 O 4 -HA) to 15.7 (for Fe 3 O 4 -APTES) nm as reported in Table 1 .…”

“…In the case of Fe 3 O 4 /HA, the absence of Fe 2+ ions within the solution can be explained by the complete oxidation of magnetite Fe 3 O 4 to maghemite Fe 2 O 3 , according to the Mössbauer spectroscopy data ( Section 2.1.1 ). However, analyzing the same data as well as results of X-ray diffraction [ 82 ], APTES-functionalized nanoparticles contain both Fe 2+ and Fe 3+ ions. The absence of Fe 2+ ions into the Fe 3 O 4 /APTES solution can be explained by the very low concentration which can fall beyond the sensitivity limits of the employed analysis technique.…”

Synthesis of liquid biofuels from biomass by hydrothermal gasification: A critical review

“…16. Hydrocarbon selectivity vs. CO conversion for (A) cobalt-based catalysts and (B) iron-based catalysts in the FT process (Data obtained from Refs [130,[163][164][165][166][171][172][173][174][175][176][177][178][179]…”