title: 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-C4olefins, 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.
authors.affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University , Universteitsweg 99, 3584 CG Utrecht, The Netherlands.
authors.forename: Jingxiu
authors.initials: J
authors.lastname: Xie
authors.affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University , Universteitsweg 99, 3584 CG Utrecht, The Netherlands.
authors.forename: Hirsa M
authors.initials: HM
authors.lastname: Torres Galvis
authors.affiliation: Dow Benelux B.V., P.O. Box 48, 4530 AA Terneuzen, The Netherlands.
authors.forename: Ard C J
authors.initials: AC
authors.lastname: Koeken
authors.affiliation: Dow Benelux B.V., P.O. Box 48, 4530 AA Terneuzen, The Netherlands.
authors.forename: Alexey
authors.initials: A
authors.lastname: Kirilin
authors.affiliation: Fundamental Aspects of Materials and Energy Group, Delft University of Technology , Mekelweg 15, 2629 JB Delft, The Netherlands.
authors.forename: A Iulian
authors.initials: AI
authors.lastname: Dugulan
authors.affiliation: Dow Benelux B.V., P.O. Box 48, 4530 AA Terneuzen, The Netherlands.
authors.forename: Matthijs
authors.initials: M
authors.lastname: Ruitenbeek
authors.affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University , Universteitsweg 99, 3584 CG Utrecht, The Netherlands.
authors.forename: Krijn P
authors.initials: KP
authors.lastname: de Jong
keywords: FTO; Fischer−Tropsch; iron; lower olefins; sintering; stability; synthesis gas