Fischer–Tropsch synthesis: effect of Cu, Mn and Zn addition on activity and product selectivity of cobalt ferrite

Abstract

The effect of Cu, Mn and Zn addition on cobalt ferrite was investigated for Fischer-Tropsch synthesis (FTS).Oxalate co-precipitation followed by decomposition under inert conditions was used to obtain various metal containing cobalt ferrites (Co 0.7 M 0.3 Fe 2 O 4 ). The carburization of cobalt ferrite in flowing CO at 270 C and 175 psig yielded iron carbides (c-Fe 5 C 2 and 3 0 -Fe 2.2 C) along with a bimetallic FeCo alloy. The extent of carburization was compared among Cu, Mn, and Zn doped catalysts with undoped cobalt ferrites under similar conditions. XRD and Mössbauer spectroscopy analysis of the freshly carburized samples followed by passivation revealed that carburization of cobalt ferrite did not change appreciably with addition of Cu or Mn. On the other hand, Zn was found to retard the carburization of cobalt ferrite. Analysis of the used FT catalysts suggests that Cu is less efficient over Mn and Zn in stabilizing the iron carbides (i.e., active form of iron) during FT synthesis. The FT activity remains more or less the same for the undoped, Cu and Zn containing cobalt ferrites at higher temperatures. The CO conversion of Co 0.7 Mn 0.3 Fe 2.0 catalyst was much lower than the other catalysts tested. Addition of Zn or Mn to cobalt ferrite was found to promote alcohol formation, particularly at higher reaction temperatures. The water-gas shift activity of the catalysts was found to decrease in the following order, Co 1.0 Fe 2.0 > Co 0.7 Mn 0.3 Fe 2.0 > Co 0.7 Zn 0.3 Fe 2.0 > Co 0.7 Cu 0.3 Fe 2.0 .

Sodium‐Containing Spinel Zinc Ferrite as a Catalyst Precursor for the Selective Synthesis of Liquid Hydrocarbon Fuels

“…As mentioned above, ZnO is a structural promoter that retards the sintering of the Fe particle size and, thus, increases the exposure of the active Fe metal surface. Usually, ZnO has a strong interaction with iron particles under FT or CO hydrogenation conditions . In contrast, Na is an electronic promoter that provides electrons to form reduced iron species as the active catalytic sites.…”

“…Usually,Z nO has a strong interaction with iron particles under FT or CO hydroge- nation conditions. [26] In contrast, Na is an electronic promoter that provides electrons to form reduced iron species as the active catalytic sites. Iron metal and Fe 3 O 4 are active sites for the formation of hydrocarbons and RWGS reactions, respectively,i nF Ts ynthesis.…”

Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

“…High-surface area, nanocrystal metal carbides are finding increased application in catalysis but can be difficult to isolate as a pure phase due to carbon diffusivity. − An important industrial catalyst used in the Fischer–Tropsch synthesis (FTS) is iron carbide and its mixed transition-metal carbide variants. − FTS converts syngas to alkanes at the surface of transition-metal carbides (Fe 5 C 2 , Fe 7 C 3 , Fe 3 C, or Fe 2 C) to produce hydrocarbons and olefins. Recent studies have shown that the chain length of the alkane depends on the transition-metal carbide composition due to contributions from a side reaction known as the water–gas shift (WGS). − ,, The WGS is the reaction between H 2 O and CO allowing for the formation of H 2 and CO 2 . This reaction is catalyzed in pure iron carbide systems, resulting in the isolation of longer and less desirable hydrocarbons with increasing water content. − The incorporation of cobalt into the iron carbide inhibits the WGS side reaction, ,, enhances catalyst stability, , but unfortunately, the pure CoC 3 is unreactive and Co is more than 2 orders of magnitude more expensive. , Generating catalysts of known Co composition can allow the balance of selectivity and cost to be assessed for the FTS; however, to date, few reports have shown the successful incorporation of Co into Fe x C y nanometals. − Translation of the bulk catalysts to nanocrystal metal carbides can allow exploration of catalytic activity through control of composition, crystallographic phase purity, and faceting. ,, …”

“…Recent studies have shown that the chain length of the alkane depends on the transition-metal carbide composition due to contributions from a side reaction known as the water−gas shift (WGS). [4][5][6]9,10 The WGS is the reaction between H 2 O and CO allowing for the formation of H 2 and CO 2 . This reaction is catalyzed in pure iron carbide systems, resulting in the isolation of longer and less desirable hydrocarbons with increasing water content.…”

First-principles study on structural, electronic, magnetic and thermodynamic properties of lithium ferrite LiFe5O8

“…In addition to the Co substitution, several investigations properties of LFO with different magnetic states, gures for crystalline structure of b-phase with a space group of Fd3m, total DOS as a function of U parameter value, orbital-projected DOS for Fe and O atoms calculated by DFT + U approach, frequency-dependent dielectric constant, Helmholtz free energies as a function of temperature and reported that the material properties can be effectively tuned by substituting Cu, Mn and Zn atoms for the Fe atom in LFO. [24][25][26] Such substitutions can denitely lead to improvements in performance of the LFO-based devices, such as microwave and permanent magnets compared with the pure LFO.…”