Short Communication Synthesis of Fe 3 O 4 -nanocatalysts with different morphologies and its promotion on shifting C 5 + hydrocarbons for Fischer–Tropsch synthesis Junling Tu a,b , Mingyue Ding a , Yulan Zhang a,b , Yuping Li a , Tiejun Wang a, ⁎, Longlong Ma a , Chenguang Wang a , Xinjun Li a a CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, PR China b University of Chinese Academy of Sciences, Beijing 100049, PR China abstract article info Article history: Received 25 August 2014 Received in revised form 19 October 2014 Accepted 21 October 2014 Available online 29 October 2014 Keywords: Fe 3 O 4 nanocatalyst Morphology-defined nanoparticle Fischer–Tropsch synthesis The shape-defined Fe 3 O 4 nanocatalysts such as spheres and polyhedrons prepared by a simple solvothermal method without calcination were applied in Fischer–Tropsch synthesis (FTS), which showed excellent catalytic activity and C 5 + selectivity compared to the traditional Fe catalyst. Especially, the Fe 3 O 4 nanocatalyst with nano- spheres (FNS) displayed higher catalytic activity and C 5 + selectivity (N 64%) than the Fe 3 O 4 nanopolyhedrons (FNP). It was found that FNS was more favorable to the reduction and dispersion of iron species as well as forma- tion of surface carbonaceous species (especially for χ-Fe 5 C 2 ) compared to FNP, which provided more active sites for FTS and facilitated the product distribution shifting towards heavy hydrocarbons. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Fischer–Tropsch synthesis (FTS), as an important technology in the production of liquid fuels and chemicals from biomass, coal and natural gas, is receiving a renewed interest for both academic and industrial ap- plications [1,2]. The process became fairly popular over the years due to the concerns about the depletion of fossil-fuel reserves and increasingly stringent environmental regulations. Iron-based catalysts are used widely in the commercial FTS processes because of its high FTS activity, low cost, flexible product distribution and favorable engineering char- acteristics [3,4]. Lately, interest has grown markedly in metal nanoparticles as cata- lysts for various processes, Fischer–Tropsch synthesis in particular [5–7]. However, it is difficult to adjust directly the selectivity of FTS due to Anderson–Schulz–Flory (ASF) distribution of hydrocarbons. It is suggested that the physical and chemical properties of a catalyst particle are sensitive to both the crystal size and shape [8]. Thus, the shape- dependent catalytic behavior is attracting more and more attention for heterogeneous catalysts. The results of Zhou et al. [9] indicated that the CuO nanoplatelets were more active for CO oxidation than the nanobelts. Somorjai et al. [10] found that the catalytic selectivity of benzene hydrogenation for the Pt catalysts was affected strongly by the nanoparticle shape (cubic and cuboctahedral). In addition, in the oxygen-reduction reaction the activity of Pd nanocrystals had the strong morphological dependence [11]. Although the shape of nanocatalysts has obvious influences on the catalytic activity and selectivity, limited results have been reported for the effects of the particle morphology on the Fe-based FTS catalysts [12,13]. In this study, the Fe 3 O 4 nanocatalysts with different morphologies (spheres and polyhedrons) were prepared by an improved one-step solvothermal method [14,15]. The shape of nanoparticles optimized distinctly the FTS activity and shifted the product distribution towards C 5 + hydrocarbons compared with the traditional Fe catalysts. Further- more, the shape of Fe 3 O 4 nanospheres facilitated the dispersion of iron species and formation of active iron carbides compared to the Fe 3 O 4 nanopolyhedrons, which further improved the catalytic activity and the formation of heavy hydrocarbons. 2. Experimental 2.1. Catalyst preparation All chemicals were used as received without any further purification. Morphology-defined iron catalysts were prepared by an improved solvothermal method. Fe 3 O 4 nanospheres (FNS) synthesis: FeCl 3 ·6H 2 O (1.35 g) was dis- solved in ethylene glycol (40 ml) to form a clear solution, followed by the addition of NaAc (3.6 g), ethylenediamine (5 ml) and polyvinylpyr- rolidone (PVP, 1.0 g). The mixture was stirred vigorously for 30 min and then sealed in a Teflon lined stainless-steel autoclave (50 ml capacity). The autoclave was heated at 473 K for 10 h, and then cooled to room temperature. The black products were washed several times with etha- nol and dried at 333 K for 6 h. Catalysis Communications 59 (2015) 211–215 ⁎ Corresponding author. Tel.: +86 20 87057751; fax: +86 20 87057737. E-mail address: wangtj@ms.giec.ac.cn (T. Wang). http://dx.doi.org/10.1016/j.catcom.2014.10.019 1566-7367/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom