Preparation and optimization of mixed iron cobalt oxide catalysts for conversion of synthesis gas to light olefins Ali Akbar Mirzaei a, * , Razeieh Habibpour a , Eslam Kashi b a Department of Chemistry, Faculty of Sciences, Sistan and Baluchestan University, P.O. Box 98135-674, Zahedan, Iran b Department of Chemical engineering, Faculty of Engineering, Sistan and Baluchestan University, P.O. Box 98164, Zahedan, Iran Received 26 June 2005; received in revised form 3 August 2005; accepted 17 August 2005 Available online 13 October 2005 Abstract Iron cobalt oxides were prepared using co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables such as the precipitate ageing time and [Fe]/[Co] molar ratio of the precipitation solution were investigated in detail. The preparation procedure and also the optimum preparation conditions were identified with respect to the catalyst activity for the hydrogenation of carbon monoxide. The results are interpreted in terms of the structure of the active catalyst and it has been generally concluded that the catalyst containing 40% Fe/60% Co – on molar basis – and aged for 2 h, is the most active catalyst for the conversion of synthesis gas to ethylene and propylene. The effect of different promoters and supports along with loadings of optimum support and promoter on the activity and selectivity of this catalyst are studied. It was found that the catalyst containing 40% Fe/60% Co/15 wt.% SiO 2 /1.5 wt.% K is an optimum modified catalyst and gave the best activity and selectivity. The activity and selectivity of all prepared catalysts have been studied in a fixed bed micro reactor in a range of reactor temperatures using synthesis gas with different H 2 /CO molar feed ratios. The lifetime of optimum catalyst for 72 h has been tested under the optimum reaction conditions and the catalyst was found to be highly stable. Characterization of both precursors and calcined catalysts by X-ray diffraction and scanning electron microscopy showed that the precipitate ageing time and also the [Fe]/[Co] ratio of the precipitation solution influenced the catalyst precursor structure and morphology. # 2005 Elsevier B.V. All rights reserved. Keywords: Catalyst preparation; Co-precipitation; Effect of ageing; Iron-cobalt oxide; Fischer–Tropsch synthesis; Light olefins 1. Introduction Mixed oxide catalysts are important commercially in conversion of synthesis gas to desired products [1–4]. The Fe-Mn and Co-Mn catalysts, with or without alkaline promoters, are the most studied [5–7]. The high selectivity of Fe-Mn catalysts in C 2 –C 4 has been correlated to the presence of a Fe-Mn spinel oxide. Unfortunately, since carbide phases are formed during the catalytic tests, catalysts have short lifetimes. Cobalt does not carburize as readily as iron under CO/ H 2 atmosphere and numerous studies have confirmed its efficiency for obtaining light olefins [8]. The protection of the spinel phase under the reaction conditions and the presence of a metallic phase, which does not carburize under test, seem to be essential to produce C 2 –C 4 olefins from CO/H 2 . Reports in the patent literature on the synthesis and study of a series of slurry phase unsupported Fe/Co Fischer–Tropsch catalysts have indicated that the addition of small amounts of Co to Fe could influence the Fe catalyst quite dramatically [9]. Indeed, this mixture could have an enhanced activity in comparison to the individual metal oxides [10]. Previous studies have shown that Co-Fe composite catalysts are efficient to produce light olefins from CO/H 2 when the cobalt ferrite is preserved under test [11]. Modification of the traditional F-T catalysts (Fe, Co, Ni, Ru) by promoters and supports has provided one means of manipulating the F-T products spectrum [12]. Due to the thermodynamic and kinetic limitations of the reaction, few catalysts are able to amplify the C 2 –C 4 hydrocarbons fraction. However, some examples are reported in the literature and these are Fe and/or Co based catalysts on partially reducible oxide supports such as MnO 2 , V 2 O 5 and TiO 2 instead of the conventional inert supports like SiO 2 and Al 2 O 3 [12–15]. It is well known that the stronger bases of the group IA metals, especially potassium, are essential promoters in iron catalysts www.elsevier.com/locate/apcata Applied Catalysis A: General 296 (2005) 222–231 * Corresponding author. Tel.: +98 541 2428247; fax: +98 541 2446565. E-mail address: mirzaei@hamoon.usb.ac.ir (A.A. Mirzaei). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.08.033