Monodisperse Nano‐Fe₃O₄ on α‐Al₂O₃ Catalysts for Fischer–Tropsch Synthesis to Lower Olefins: Promoter and Size Effects

Abstract

The Fischer–Tropsch synthesis to lower olefins (FTO) is a desirable nonpetroleum‐based route to produce basic chemicals. A novel two‐step method was applied to synthesize iron‐based supported catalysts, which is to prepare nano‐Fe3O4 first by thermal decomposition method and sequentially load them on α‐Al2O3 by impregnation. TEM and XRD results manifested that the controllable, uniform Fe3O4 nanoparticles are monodispersed on the surface of α‐Al2O3. H2‐TPR demonstrated that the reduction of Fe species was facilitated because of the weak interaction between Fe species and the support. These superior properties contribute to an enhanced catalytic activity and stability compared with the catalyst prepared by directly impregnating ammonium iron citrate on α‐Al2O3. Then, the effect of promoters was investigated at the same Fe loading and nanoparticle size. The appropriate addition of K could enhance the catalytic activity and suppress the secondary hydrogenation. On the contrary, S has a negative impact on CO conversion and strongly decreases C5+ selectivity. Particularly, the combination of K and S could obtain more pronounced CO conversion and higher lower olefins selectivity (≈40 %). Furthermore, size effects were explored by precisely tailoring the iron oxide particle size with the Fe loading kept constant. It was found that 12.0 nm nano‐Fe3O4 on α‐Al2O3 with or without K plus S promoters showed the best catalytic activity among the catalysts with different particle size.

Hydrogenation of CO to olefins over a supported iron catalyst on MgAl2O4 spinel: effects of the spinel synthesis method

“…As is well accepted, the FTO catalyst must be activated by reduction and carburization before the reactions, and the reduction and carburization of iron oxides have a signicant inuence on the performance of the catalyst. 57 The hydrogen temperatureprogrammed reduction (H 2 -TPR) can verify the reduction ability, and to conrm the interaction between iron and the support. Fig.…”

“…5 Besides, the acidity of the support exerts its inuence on its interaction with the active phase, and on the catalytic performance. [6][7][8][9] The Hägg iron carbide (c-Fe 5 C 2 ) has been generally accepted as the active phase for the FT reactions. [10][11][12] Many previous works found that the c-Fe 5 C 2 crystal facet greatly affects the catalytic performance and the formation of the Hägg iron carbide strongly depends on the interaction between the iron species and the support.…”

Beyond Cars: Fischer‐Tropsch Synthesis for Non‐Automotive Applications

“…Olefin, especially lower olefin (C 2 ‐C 4 ), is a series of crucial basic building‐block chemicals for production of a wide range of plastics, solvents, drugs, and cosmetics. Lower olefins are generally produced by steam cracking of crude oil–derived naphtha, the methanol‐to‐olefins (MTO) process, or by the direct F‐T route (FTO) from a coal‐based feedstock syngas . A large amount of studies has been devoted to syngas conversion to lower olefins by F‐T synthesis over Fe catalysts as they are more selective towards olefins than Co or Ru F‐T catalysts.…”

Carbon–Silica Composite as an Effective Support for Iron Fischer–Tropsch Synthesis Catalysts

“…The performance of iron catalysts can be greatly improved by adding “electronic” or chemical promoters to the catalyst formula . Among such promoters, potassium, sodium, copper, and manganese have been proposed. Recently, the TPR‐EXAFS technique confirmed that doping FTS catalysts with copper and alkali metals remarkably promotes the carburization rate relative to the undoped catalyst.…”