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

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

Xie, Jingxiu (Universiteit Utrecht)
Torres Galvis, Hirsa M. (Universiteit Utrecht)
Koeken, Ard C J (Dow)
Kirilin, Alexey (Dow)
Dugulan, A.I. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Ruitenbeek, Matthijs (Dow)
de Jong, Krijn P. (Universiteit Utrecht)

2016

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.

Fischer−Tropsch
FTO
iron
lower olefins
synthesis gas
stability
sintering

http://resolver.tudelft.nl/uuid:dd9ec35f-99b5-4238-ab79-5cb3db00ef49

https://doi.org/10.1021/acscatal.6b00321

2155-5435

ACS Catalysis, 6 (6), 4017-4024

Institutional Repository

journal article

© 2016 Jingxiu Xie, Hirsa M. Torres Galvis, Ard C J Koeken, Alexey Kirilin, A.I. Dugulan, Matthijs Ruitenbeek, Krijn P. de Jong