Size and Promoter Effects on Stability of Carbon-Nanofiber-Supported Iron-Based Fischer–Tropsch Catalysts

Abstract

The Fischer–Tropsch Synthesis converts synthesis gas from alternative carbon resources, including natural gas, coal, and biomass, to hydrocarbons used as fuels or chemicals. In particular, iron-based catalysts at elevated temperatures favor the selective production of C2–C4 olefins, which are important building blocks for the chemical industry. Bulk iron catalysts (with promoters) were conventionally used, but these deactivate due to either phase transformation or carbon deposition resulting in disintegration of the catalyst particles. For supported iron catalysts, iron particle growth may result in loss of catalytic activity over time. In this work, the effects of promoters and particle size on the stability of supported iron nanoparticles (initial sizes of 3–9 nm) were investigated at industrially relevant conditions (340 °C, 20 bar, H2/CO = 1). Upon addition of sodium and sulfur promoters to iron nanoparticles supported on carbon nanofibers, initial catalytic activities were high, but substantial deactivation was observed over a period of 100 h. In situ Mössbauer spectroscopy revealed that after 20 h time-on-stream, promoted catalysts attained 100% carbidization, whereas for unpromoted catalysts, this was around 25%. In situ carbon deposition studies were carried out using a tapered element oscillating microbalance (TEOM). No carbon laydown was detected for the unpromoted catalysts, whereas for promoted catalysts, carbon deposition occurred mainly over the first 4 h and thus did not play a pivotal role in deactivation over 100 h. Instead, the loss of catalytic activity coincided with the increase in Fe particle size to 20–50 nm, thereby supporting the proposal that the loss of active Fe surface area was the main cause of deactivation.

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

“…Despite novel catalysts including OX‐ZEO and cobalt carbide have been reported to obtain a high lower olefins selectivity with a relative lower CO conversion, iron‐based catalysts still arouse much more attention because of their low cost, tolerance for CO/H 2 ratio, resistance to contaminants, and feasibility in industry. Generally, particle size of Fe species, promoter, Fe precursor and support should be taken into account to design iron‐based FTO catalyst.…”

Attachment of Iron Oxide Nanoparticles to Carbon Nanotubes and the Consequences for Catalysis

“…[7,8] FTO involves iron-based catalysts and is becoming increasingly important as an alternative to the traditional cracking of crude oil fractions for the production of lower olefins (C2-C4) and aromatics from syngas (CO/H 2 ). [16][17][18][19] By promoting ironp articles with Na and Sp romoters, low selectivity to methane and high selectivity to olefins can be obtained. [14,15] To increase the activity and selectivity of an FTO catalyst, the addition of promoters is of vital importance,a su npromoted iron catalysts usually show high selectivity towards methane.…”

Bifunctional Catalysis for the Conversion of Synthesis Gas to Olefins and Aromatics

“…The addition of sodium and sulfur as promoters to an iron‐based Fischer–Tropsch synthesis catalyst led to enhancement of activity and selectivity to lower olefins . Now, we show that the combination of such a catalyst with a zeolite shows increased selectivity to chemicals of up to 73 % C , whereas the product spectrum is extended to aromatics.…”