Identification of carbon species on iron-based catalysts during Fischer-Tropsch synthesis

Abstract

This paper focuses on the use of in situ and ex situ characterisation techniques to provide evidences of carbon species on a commercial iron-based Fischer-Tropsch synthesis catalyst as well as other indices of potential deactivation mechanisms. In situ XANES measurements demonstrate that re-oxidation or transformation of the active iron phase, i.e. the Hägg carbide phase, was not a significant deactivation mechanism at the studied conditions. Sintering of Hägg carbide nanoparticles is significant with increasing temperatures and time on stream. The sintering mechanism is proposed to be a hydrothermally-assisted process. In situ DRIFTS indicates the presence of different carbon species on the catalyst surface such as aliphatic hydrocarbons from wax products and oxygenate compounds such as alcohols, aldehydes/ketones and carboxylate species. Carboxylate species are resistant towards hydrogenation at 280°C. The presence of different carbon species on the surface after wax product extraction is evident from TPH-MS measurements. GC-MS analysis shows that the strongly adsorbed carbon species remaining on the catalyst surface from wax products are mainly α-olefins and branched carboxylic species. The interaction of oxygenate compounds, especially carboxylate species with iron oxide, may form stable complexes limiting further iron catalyst carburization. STEM-EDX analysis shows that carbon is preferentially located on iron particles.

Comparative Studies of Fischer-Tropsch Synthesis on Iron Catalysts Supported on Al2O3-Cr2O3 (2:1), Multi-Walled Carbon Nanotubes or BEA Zeolite Systems

“…Fischer-Tropsch synthesis is a promising catalytic route for the environmentally friendly production of fuels from biomass, coal and natural gas [1][2][3][4][5]. However, on an industrial scale, a very efficient and stable catalyst is desirable.…”

“…Both of these features can be achieved using bifunctional catalysts. One of the main reasons for the deactivation of Fischer-Tropsch catalysts is the deposition of carbon [5,21,22]. The formations on the catalyst surface carbon deposit blocks the active sites of the catalyst, leading to its deactivation [23].…”

“…Based on the above-presented suggestions, the main aim of the work was to carry out comparative investigations of iron systems for the Fischer-Tropsch process and reveal the link between their physicochemical and catalytic properties. It is well known that the catalytic activity of heterogeneous catalysts in the chemical process depends on the nature, dispersion and reactivity of the active centres in relation to the substrates; on the steric effects and diffusion of the reagents; and on the created products in the catalytic material pores [5]. That is why, in our studies, we used various support materials whose structure can affect the transport of reagents and products from and to the catalyst bed with different specific surface areas and various reducing and acidic properties.…”

Preparation of Iron Carbides Formed by Iron Oxalate Carburization for Fischer–Tropsch Synthesis

“…Three peaks were observed in the used IO-350 • C and IO-450 • C catalysts based on their reactivity towards H 2 , indicating three types of carbonaceous species [29,32]. For the used IO-450 • C catalyst, the first species at 320 • C corresponded to atomic carbon or surface carbide, the middle region between 500 and 600 • C was considered to be Fe 3 C carbide [32], and, finally, the one at the temperature above 600 • C was classified as graphitic carbons. The used IO-350 • C catalyst had amorphous carbon at 400 • C and only a small amount of graphitic carbons at 620 • C. The second species (~450 • C) belonged to the Fe 5 C 2 carbide.…”

Improving Fe/Al2O3 Catalysts for the Reverse Water-Gas Shift Reaction: On the Effect of Cs as Activity/Selectivity Promoter

“…In recent years, numerous studies have been dedicated to improving the catalytic performance of the RWGS reaction, with considerable attention on monometallic catalysts such as Pt [10] and Cu [11], bimetallic catalysts such as Cu-Ni [12], and transition metal carbide catalysts, such as Mo 2 C [13]. Among the wide variety of catalysts reviewed in literature, iron-based catalysts have shown the greatest potential, due to their thermal stability and high oxygen mobility [14,15], while remaining a credible option in terms of costs of manufacture [16]. Transition metal oxides, such as TiO 2 [17], CeO 2 [18], and Al 2 O 3 [19], have been investigated as supports for catalysts used in the RWGS reaction.…”