Applied Catalysis A: General 464–465 (2013) 269–280 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General j ourna l h om epage: www.elsevier.com/locate/apcata Palladium-promoted cobalt catalysts supported on silica prepared by impregnation and reverse micelle for Fischer–Tropsch synthesis Nattawut Osakoo a,b , Robert Henkel b , Sirinuch Loiha c , Frank Roessner b,∗∗ , Jatuporn Wittayakun a,∗ a School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand b Technische Chemie II, Carl von Ossietzky Universität Oldenburg, Oldenburg D-26111, Germany c Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand a r t i c l e i n f o Article history: Received 5 March 2013 Received in revised form 30 May 2013 Accepted 7 June 2013 Available online xxx Keywords: Fischer–Tropsch synthesis Cobalt Palladium Silica Impregnation Reverse micelle a b s t r a c t The objectives of this work were to compare physicochemical properties of silica-supported cobalt cat- alysts (with 10 wt% Co) prepared by impregnation (10Co-IP) and precipitation using a reverse micelle technique (10Co-RM) and to investigate influence of palladium as a promoter (0.2 wt% and 1.0 wt%) on properties of 10Co-IP and 10Co-RM. The catalysts were characterized by XRD, H 2 -TPR, DR-UV–vis, XANES, EXAFS and the reactivity during Fischer–Tropsch synthesis (FTS) was tested at 230 ◦ C, 5 bar with H 2 /CO = 2. The particle size of Co 3 O 4 in 10Co-IP was larger than that of 10Co-RM which could contribute to lower selectivity to methane and C 2 –C 4 paraffin products. The addition of 0.2 wt% Pd to 10Co-IP and 10Co-RM enhanced the cobalt reducibility, FTS activity and paraffin selectivity. On the other hand, the addition of 1.0 wt% Pd resulted in increased methane formation and lower CO conversion. The most suitable cata- lyst from this work was 0.2Pd-10Co-IP that gave high CO conversion (34.8%) and high mole fraction of paraffins (0.38) in the gasoline range (C 5 –C 9 ). © 2013 Elsevier B.V. All rights reserved. 1. Introduction The Fischer–Tropsch synthesis (FTS) is a reaction of syngas, which is a mixture of carbon monoxide (CO) and hydrogen (H 2 ) to produce hydrocarbon and oxygenated compounds [1]. The FTS process is interesting in both industrial and academic fields due to the limited petroleum resources and increasing oil price [2,3]. Among several catalysts for the FTS process, cobalt in metal- lic form (Co 0 ) is widely used because it can be employed at low temperature and gives high selectivities for C 5+ products. The cat- alytic activity and product selectivity are a function of reducibility of cobalt, which depends on the dispersion [4,5]. In order to improve dispersion of metallic particles, cobalt precursors are dispersed on porous materials such as SiO 2 , Al 2 O 3 , and TiO 2 . However, the reduc- tion of Co species depended on the metal–support interactions which decreased in the order Al 2 O 3 > TiO 2 > SiO 2 [6]. Although weak metal–support interactions between Co and SiO 2 support could attribute to a poor metal dispersion resulting in low CO conver- sion, the Co/SiO 2 gave the highest C 5+ selectivity [6]. Consequently, ∗ Corresponding author. Tel.: +66 44 224 256; fax: +66 44 224 185. ∗∗ Co-corresponding author. E-mail addresses: frank.roessner@uni-oldenburg.de (F. Roessner), jatuporn@sut.ac.th (J. Wittayakun). SiO 2 is still one of the most widely used catalyst supports for FTS reaction because it can stabilize the active phase against loss of surface area during the reaction and to facilitate the mass or heat transfer in the reactions [7]. The cobalt dispersion on SiO 2 depends on the preparation method [7]. Zhang et al. [8] studied silica-supported cobalt cat- alysts (Co/SiO 2 ) prepared by incipient wetness impregnation (IP) with cobalt nitrate in various solvents and found that the catalyst prepared from dehydrated ethanol had the highest dispersion and gave the best catalytic performance. Another method to produce cobalt catalyst with high dispersion is the precipitation using the reverse micelle method (RM). Fischer et al. [9] used the RM method to synthesize Co 3 O 4 crystallites in the nanometer size range (aver- age sizes: 3–10 nm) supported on Al 2 O 3 (Co/Al 2 O 3 ). The cobalt in Co/Al 2 O 3 from RM method contained metal with mainly a face- centered cubic (fcc) phase whereas that prepared by conventional method consisted of the mixed fcc and hexagonal close packed (hcp) [10,11]. The catalytic activity of supported cobalt catalyst also depends on cobalt reducibility. To enhance the reducibility of cobalt, which is well dispersed on a support, a small amount of noble metal such as Ru, Pt, Pd, Ir or Re can be added [1,3,7,12–15]. There are several reports about the use of Ru as a promoter for cobalt catalysts in the FTS process to enhance cobalt reducibility and CO conver- sion [1,13,14]. Other promoters including Pd are not extensively 0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2013.06.008