Please cite this article in press as: J. Zhu, et al., Compact reactor for Fischer–Tropsch synthesis based on hierarchically structured Co catalysts: Towards better stability, Catal. Today (2013), http://dx.doi.org/10.1016/j.cattod.2013.03.010 ARTICLE IN PRESS G Model CATTOD-8379; No. of Pages 10 Catalysis Today xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Catalysis Today jou rn al h om epage: www.elsevier.com/locate/cattod Compact reactor for Fischer–Tropsch synthesis based on hierarchically structured Co catalysts: Towards better stability Jun Zhu a , Jia Yang a , Andreas Helland Lillebø a , Ye Zhu a , Yingda Yu b , Anders Holmen a , De Chen a,∗ a Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, N-7491, Norway b Department of Materials Technology, Norwegian University of Science and Technology (NTNU), Trondheim, N-7491, Norway a r t i c l e i n f o Article history: Received 2 November 2012 Received in revised form 8 January 2013 Accepted 4 March 2013 Available online xxx Keywords: Fischer–Tropsch synthesis Cobalt Nanotubes Catalyst deactivation Structured catalyst Stability a b s t r a c t A compact reactor for Fischer–Tropsch (F–T) synthesis based on hierarchically structured Co catalysts has been developed. The SiO 2 coated carbon nanofiber (CNF)/carbon felt (CF) has several advantages, such as high surface area, low pressure drop, high thermal conductivity and good mass transport properties. CNFs were grown on the microfibers of CF, which greatly increased the surface area of the composite. An in situ sol–gel method has been developed to coat one thin layer of SiO 2 to form CNF/CF@SiO 2 core shelled tubes. The efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature gradient during the F–T synthesis without adding any diluents. The prepared Co/(CNF/CF@SiO 2 ) catalysts have higher activity and C 5+ selectivity. The catalyst stability is also greatly enhanced by manipulating the Co-support interface by means of the coated SiO 2 layer on CNFs. Reduction–oxidation (Redox) cycles indicate that the SiO 2 layer decreases the oxidation potential of the Co nanoparticles, with enhanced catalytic stability as a result. © 2013 Published by Elsevier B.V. 1. Introduction Fischer–Tropsch (F–T) synthesis is one of the most promising routes for modern Gas-to-Liquids (GTL) technology [1]. It produces a complex mixture of hydrocarbons, consisting of methane, C 2+ olefins, paraffins and oxygenates. The product distribution is dependent on the type of catalyst and on the reaction conditions. Normally, high catalyst activity, high C 5+ selectivity, slow deacti- vation rates, and high mechanical strength are required for the F–T catalysts. Supported cobalt is the preferred catalyst for the F–T synthesis of long chain paraffins from natural gas due to their high activity and selectivity to C 5+ , low water-gas shift activity and relatively low price [2]. Mass transfer effects are very important for the activity and selectivity in the F–T synthesis. Even though the reactants are in the gas phase, the catalyst pores will be filled with liquid prod- ucts. Diffusion in the liquid phase is about 3 orders of magnitude slower than in the gas phase and even slow reactions may become diffusion limited. Diffusion limitations may occur through limita- tion on the arrival of CO to the active sites or through the limited removal of reactive products [2,3]. F–T synthesis is a highly exother- mic reaction and efficient removal of heat is critical for obtaining a ∗ Corresponding author. Tel.: +47 735 93149, fax: +47 735 95047. E-mail address: de.chen@ntnu.no (D. Chen). high C 5+ selectivity and low selectivity of methane. Consequently, numerous efforts have been developed to improve both the mass and heat transfer in the F–T synthesis [2,4]. We have previously used monolithic reactor/catalyst [5–7] to study the F–T synthe- sis. It offers several possible advantages compared to other F–T reactors, such as high gas–liquid mass transfer rates in two phase flow, short diffusion distance in monolith walls, plug flow char- acteristics, high liquid and gas throughputs, low pressure drop, no wax-catalyst separation necessary and accurate temperature control by direct cooling of catalyst with the liquid medium and external heat removal. The previous results have shown that the monolithic substrate gave about the similar activity and selectivity as the powdered catalyst [5–7]. However, there is a drawback of the monolith reactor that the activity per reactor volume is relatively low. In the last decade, carbon nanotube (CNT) and nanofiber (CNF), with relative high surface area, chemical resistance to acids and bases, and good thermal and electric conductivity, have been exten- sively studied as promising supports for active metals and oxides [8–13]. CNF supported cobalt catalyst has shown superior activ- ity and C 5+ selectivity compared with conventional cobalt catalysts supported on alumina for F–T synthesis [14]. Using hierarchically structured carbon nanofibers/carbon felt composites (CNF/CF) as a support material for cobalt nanoparticles in the highly exother- mic F–T synthesis offer several advantages, such as improved heat and mass transfer, relatively low pressure drop, and safe handling 0920-5861/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.cattod.2013.03.010