Chemical Engineering Science 65 (2010) 214--219 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces A new preparation method of Au/ferric oxide catalyst for low temperature CO oxidation Shinji Kudo, Taisuke Maki, Masahiro Yamada, Kazuhiro Mae ∗ Department of Chemical Engineering, Graduate School of Engineering, Kyoto University, Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan ARTICLE INFO ABSTRACT Article history: Received 27 June 2008 Received in revised form 25 May 2009 Accepted 27 May 2009 Available online 6 June 2009 Keywords: Catalysis CO oxidation Fuel Gold catalyst Particle Precipitation A new preparation method of Au/-Fe 2 O 3 catalyst for CO oxidation reaction was proposed in this paper. The method includes only a simple modification of the conventional coprecipitation method, adding HAuCl 4 solution after the growth of iron hydroxide grain to a certain size, but significantly influenced the catalytic activity in the reaction. In the characterization study, XRD (X-ray diffractometer) analysis, TEM (transmission electron microscope) observation, and N 2 adsorption measurement showed similar results among the samples calcined at the same temperature, but the effect of the preparation method appeared in the CO adsorption measurement among the samples calcined at 200 ◦ C. Catalysts having high CO adsorption ability also performed well in CO oxidation tests. The CO adsorption and oxidation studies indicated that the proposed preparation method results in stable and effective loading of Au, compared to the conventional coprecipitation method. In the CO oxidation test, the catalyst prepared by the proposed mixing scheme achieved complete CO conversion for more than 3000 h at 25 ◦ C, space velocity 100,000 h -1 , and 500 ppm CO. The selectivity for the CO oxidation was confirmed using reformed gas containing excess H 2 . In addition, the NO reduction reaction was favored over CO oxidation by the catalyst. Thus, we were able to load Au on the -Fe 2 O 3 effectively and demonstrate its potential as an environmental catalyst. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Environmental pollutants produced on consumer sites are in- creasing along with the growth of civilian activities. Removal of these pollutants is required to reduce the environmental burden, but the technique is not yet sufficiently developed for non-industrial use be- cause of environmental pollutant characteristics such as low concen- tration of ppb–ppm, high concentrations of reaction inhibitors, and volatile reaction conditions (Iwamoto, 2001). Then, catalysts used in practice are often useless as an environmental catalyst. In addition, environmental catalysts used for on-site pollutant removal should have a long-term stability and catalytic activity at low temperature. Commonly used electric appliances and poor combustion of fossil fuel can accumulate CO in an enclosed space. Carbon monoxide is highly toxic; the exposure to several hundreds ppm CO can be lethal. Thus, CO can be regarded as one of the most dangerous and imminent environmental pollutants for human beings. Therefore, its removal is necessary for safe habitation. In addition, CO removal techniques are required in polymer electrolyte fuel cell (PEFC) usage, where the CO concentration in the hydrogen rich gas must be selectively ∗ Corresponding author. Tel.: +81 75 383 2668. E-mail address: Kaz@cheme.kyoto-u.ac.jp (K. Mae). 0009-2509/$ - see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2009.05.044 reduced to less than 100 ppm (Choudhary and Goodman, 2002; Wee and Lee, 2006). Low temperature CO oxidation by catalysts has been widely studied since the discovery of the active nano-sized gold attached to metal oxides by Haruta et al. (1989). A wide variety of metal oxides can act as the support, and appropriately prepared catalysts have high activity, even below 0 ◦ C(Haruta, 1997; Haruta et al., 1993; Avgouropoulos et al., 2002). However, existing catalysts have limited long-term stability, reactivity at severe reaction conditions, and reproducibility (Sakurai et al., 2004; Schubert et al., 2001; Schumacher et al., 2003; Park and Lee, 1999; Wolf and Sch ¨ uth, 2002; Li et al., 2006). Currently, it appears that CO oxidation occurs at the interface between a gold particle and the support material (Daniells et al., 2005; Haruta, 2004). Then, the control of the bonding state originating from the size of the gold particles and the physico- chemical properties of the supports is important for the genesis of catalytic activity (Kozlov et al., 1999). The limitations mentioned above seem to be largely due to the unstable bonding state. The size of the gold particles depends significantly on the dispersion and bonding state of the gold on the support when it is attached, as well as the calcination temperature. Unique preparation meth- ods reported by various authors focused on this point and tried to refine the gold catalyst prepared with the conventional coprecipita- tion method (Haruta et al., 1993; Andreeva et al., 1998; Kobayashi