Development of cobalt–copper nanoparticles as catalysts for higher alcohol synthesis from syngas Nachal Devi Subramanian a , G. Balaji b , Challa S.S.R. Kumar b , James J. Spivey a, * a Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70802, USA b Center for Advanced Microstructures & Devices, Louisiana State University, Baton Rouge, LA 70806, USA 1. Introduction With today’s increasing oil prices and declining fossil fuel resources, there is a need to look for alternative commercially viable energy sources. Bio-based fuel resources, particularly ethanol, have been studied extensively in the recent years as clean, sustainable and transportable fuel alternatives [1]. One promising process for bio-fuel production involves the conversion of bio-derived synthesis gas (syngas) to fuels and oxygenates. Syngas derived from biomass or coal is particularly interesting since both sources are abundant, and biomass is a renewable feedstock [2]. It is well known that syngas conversion to C 2+ oxygenates is often limited by the formation of methane and methanol. However, C 2+ alcohols are more desirable products, both as neat fuels [3–5], fuel additives or as a carrier for hydrogen to supply fuel cells. In addition to its potential application as a transportation fuel, ethanol has been considered as a feedstock for the synthesis of variety of chemicals, fuels and polymers [6,7]. It is estimated that ethanol could replace as much as one-third of the domestic petroleum use in the near future [8]. Hence, the development of a suitable and efficient catalyst to produce higher alcohols from syngas, coupled with an understanding of the underlying reaction mechanism, is clearly important. The general mechanism of C 2 oxygenate formation from syngas has been extensively studied and the main steps are believed to be: (a) dissociative adsorption of CO and H 2 , (b) formation of surface hydrocarbon (CH x ) ads and hydroxyl (OH) ads species and (c) CO insertion to form the C–C bond [9]. Ethanol formation is favored by a catalyst that selectively promotes the CO insertion reaction instead of the hydrogenation of the (CH x ) ads surface species, since hydrogenation of (CH x ) ads species leads to hydrocarbon formation [10]. The catalysts that have been studied for this reaction include Rh-based catalysts and alkali-promoted Cu-based catalysts [10]. Rh-based catalysts have been found, so far, to be the most selective catalysts for the synthesis of higher alcohols from CO hydrogena- tion [10]. The activity and selectivity of C 2 + oxygenate synthesis on Rh catalysts has been attributed to their ability to catalyze both CO dissociation and CO insertion [11]. However, CO dissociation on surfaces such as fcc Rh(1 1 1) is almost impossible or very slow and the presence of steps/kinks are necessary to enhance the CO dissociation rate [12]. This is in agreement with the catalytic behavior of Rh in CO hydrogenation since it has been suggested that metals which adsorb CO strong enough to activate the molecule but do not dissociate it readily are active catalysts for the formation of oxygenates [13]. However, the high cost and limited availability of the precious Rh metal catalysts [14] have led to the Catalysis Today 147 (2009) 100–106 ARTICLE INFO Article history: Available online 2 April 2009 Keywords: Co Cu Core–shell nanoparticles Syngas CO hydrogenation Higher alcohols ABSTRACT The synthesis of higher alcohols from syngas has been studied over different types of Cu-based catalysts. In order to provide control over the catalyst composition at the scale of a few nanometers, we have synthesized two sets of Co–Cu nanoparticles with novel structures by wet chemical methods, namely, (a) cobalt core–copper shell (Co@Cu) and (b) cobalt–copper mixed (synthesized by simultaneous reduction of metal precursors) nanoparticles. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalysts were tested for CO hydrogenation at temperatures ranging from 230 8C to 300 8C, 20 bar and 18,000 scc/(hr.gcat). It was observed that the Co–Cu mixed nanoparticles with higher Cu concentration exhibit a greater selectivity towards ethanol and C 2+ oxygenates. The highest ethanol selectivity achieved was 11.4% with corresponding methane selectivity of 17.2% at 270 8C and 20 bar. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 225 578 3690; fax: +1 225 578 1476. E-mail address: jjspivey@lsu.edu (J.J. Spivey). Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod 0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2009.02.027