Applied Catalysis A: General 386 (2010) 94–100 Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata Small gold particles supported on MgFe 2 O 4 nanocrystals as novel catalyst for CO oxidation Chun-Jiang Jia, Yong Liu, Manfred Schwickardi, Claudia Weidenthaler, Bernd Spliethoff, Wolfgang Schmidt, Ferdi Schüth ∗ Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany article info Article history: Received 4 May 2010 Received in revised form 2 July 2010 Accepted 20 July 2010 Available online 27 July 2010 Keywords: Supported gold catalyst MgFe2O4 CO oxidation Pretreatment atmosphere Active oxygen abstract We present the study on the catalytic performance of gold particles supported on spinel type MgFe 2 O 4 nanocrystals (Au/MgFe 2 O 4 ) which exhibit high activity for low temperature CO oxidation. Using XRD, TEM, XPS and CO titration techniques, we investigated the effect of the pretreatment atmosphere on the structure and catalytic properties of the Au/MgFe 2 O 4 catalyst in CO oxidation. TEM, XPS and XRD showed that the pretreatment atmosphere had a negligible effect on the particle size distribution, chemical states of the gold, and the structure of the support. Among the various pretreated catalysts, O 2 -Au/MgFe 2 O 4 exhibits superior activity, indicating that pretreatment in oxidative atmosphere induced the high capa- bility of the catalyst to activate CO and supply active oxygen for CO oxidation as confirmed by CO titration experiments. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Gold had been considered as a far less active catalyst than plat- inum group metals because of its inert chemical nature and its low dispersion on common support materials [1]. However, when small gold particles or clusters are supported on metal oxide in a highly dispersed state, it exhibits a surprisingly high activity for various redox reactions, in particular CO oxidation [2–4]. It is known that catalysts of gold supported on reducible transi- tion metal oxides, such as TiO 2 [5], Fe 2 O 3 [5,6], CeO 2 [7], Mn 2 O 3 [8], and Co 3 O 4 [5], exhibit significantly enhanced activities for CO oxi- dation compared to those supported on inert oxides, including SiO 2 , Al 2 O 3 , and MgO [9]. However, the relationship between activity and oxide reducibility is not straightforward. Support reducibility does not guarantee high activity, and if properly prepared and activated, gold can be very active also supported on non-reducible supports such as Al 2 O 3 [10–12] or SiO 2 [11,12]. Besides the support effect, the particle size, along with the chemical state of gold and specific metal–support interactions are also suggested to play crucial roles with respect to activity of supported gold catalysts [13–15]. The factors mentioned above are largely determined by the way the gold catalysts are prepared and activated [15]. Among various synthesis routes to prepare highly dispersed supported gold catalysts, the colloidal deposition method is an ∗ Corresponding author. Fax: +49 2083062995. E-mail address: schueth@mpi-muelheim.mpg.de (F. Schüth). interesting option [10,16,17]. Using this method, it is possible to obtain small gold particles with sizes of 1–5 nm that are highly active for CO oxidation. The high reproducibility for both the prepa- ration and the catalytic activities of the resulting catalysts has been proven [10,17–19]. An especially appealing feature of the colloidal deposition method is that the colloidal gold metal particles are gen- erated before they are deposited on the support. Thus, any influence of the support on the formation process of the gold particles is eliminated. Therefore, this route allows an unbiased evaluation of support effects on the catalyst activity. Up to now, the majority of the studies of gold catalysts for low temperature CO oxidation is focused on gold catalysts deposited on rather simple oxidic supports; there are fewer investigations on gold supported on complex oxides or salts. Recently, several groups have used metal carbonates (BaCO 3 ) [20], hydroxyap- atite (Ca 10 (PO 4 ) 6 (OH) 2 ) [21–23], orthovanadates (LaVO 4 ) [24], and spinel type oxides (MgAl 2 O 4 ) [19,25,26] as supports for Au cata- lysts. It is mentioned that high activity for low temperature CO oxidation was achieved for gold supported on inert MgAl 2 O 4 [19] that is regarded as an inactive support. The application of complex oxides or salts as supports opens a new route in the search for highly active gold catalyst for CO oxidation and other catalytic reactions. In this work, we present the first investigations on the catalytic performance of gold supported on spinel type MgFe 2 O 4 nanocrys- tals (Au/MgFe 2 O 4 ) exhibiting high activity for low temperature CO oxidation. We studied the effect of different pretreatment condi- tions, i.e., oxidative, inert, and reductive atmospheres, on particle size, chemical state of the gold, the structure of the MgFe 2 O 4 sup- 0926-860X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.07.036