Reduction behaviour of Fe/ZrO2 and Fe/K/ZrO2 Fischer–Tropsch catalysts

Abstract

The reduction behaviour (the activation process) of two iron-based Fischer-Tropsch catalysts viz. an unpromoted and a potassium-promoted zirconia-supported iron catalyst is investigated. The initial dispersion of both catalysts is very high. To establish the nature of the iron species under hydrogen atmosphere, experiments were performed at ambient pressure. It is demonstrated for both catalysts that during reduction the carbon originating from the citrate complex used in the preparation procedure is not completely removed, whereby the largest amount of the carbon species is encountered on the potassium-promoted catalyst. During reduction at ambient pressure this residual carbon reacts with metallic iron and forms cementite (θ-Fe 3 C). The iron oxide of the potassium-promoted catalyst turns out to reduce more easily than the oxide of the unpromoted catalyst. Upon formation of divalent iron, this divalent species readily reacts with the support to give a stable mixed oxide. This mixed oxide is suggested to be a prerequisite in maintaining a high dispersion of the metallic iron particles. Based on the analyses presented here, a reduction model is proposed.

On the structural, textural and morphological features of Fe-based catalysts supported on polystyrene mesoporous carbon for Fischer–Tropsch synthesis

“…Silica, alumina, molecular sieves, titania, zirconia, carbon and zeolites have been the most studied supports for FTS catalysts [1][2][3][4][5][6][7][8][9][10][11]. Iron forms mixed oxides when supported on silica or alumina due to the influence of strong metal−support interactions, which are difficult to reduce and to allow the formation of the active Fe carbide [12][13][14][15].…”

“…A c c e p t e d M a n u s c r i p t 5 The purpose of the present work is to study the use of polystyrene mesoporous carbon as a support for Fe monometallic catalysts for the Fischer-Tropsch reaction. A detailed description of two Fe-based catalysts supported on polystyrene mesoporous carbon is presented along with their influence on the selectivity of FTS products.…”

“…Many reviews on FTS have discussed the conventional process and the advantages and disadvantages of using Fe-based or Co-based catalysts to produce paraffins and olefins [5][6][7][8][9]. Slurry or tubular reactors are usually employed, which operate at temperatures and pressures ranging from 513 to 543 K and 1 to 4 MPa [9].…”

High Loading Fe-supported Fischer–Tropsch Catalysts: Optimization of the Catalyst Performance

“…On the contrary, for promoted catalysts, the selectivity seems to be less dependent on the activating gas. The carburization of iron, which is essential for the formation of catalytic activated species for FT [11,17], is most the reason of the beneficial activation effect using H 2 /CO mixture.…”

“…Many attempts have been made to prepare supported iron-based catalysts using a wide range of metal amount: 2.5% [17], 5% [16,18], 10% [11], 15.7% [15], 23% [14]. Activity and selectivity towards heavy hydrocarbons, using these catalysts, are generally lower and methane selectivity is unacceptably higher than those obtained from the use of unsupported precipitated iron catalysts [11].…”