Applied Catalysis B: Environmental 138–139 (2013) 51–61 Contents lists available at SciVerse ScienceDirect Applied Catalysis B: Environmental jo ur nal ho me p age: www.elsevier.com/locate/apcatb Synthesis of nanosized Ce 0.85 M 0.1 Ru 0.05 O 2-ı (M = Si, Fe) solid solution exhibiting high CO oxidation and water gas shift activity Vijay M. Shinde, Giridhar Madras ∗ Department of Chemical Engineering, Indian Institute of Science, Bangalore-560 012, India a r t i c l e i n f o Article history: Received 7 December 2012 Received in revised form 12 February 2013 Accepted 15 February 2013 Available online 21 February 2013 Keywords: Solid solution Ceria supported catalyst Oxygen storage capacity CO oxidation Redox mechanism Water gas shift a b s t r a c t Nanosized Ce 0.85 M 0.1 Ru 0.05 O 2-ı (M = Si, Fe) has been synthesized using a low temperature sonication method and characterized using XRD, TEM, XPS and H 2 -TPR. The potential application of both the solid solutions has been explored as exhaust catalysts by performing CO oxidation. The addition of Si- and Fe- in Ce 0.95 Ru 0.05 O 2-ı greatly enhanced the reducibility of Ce 0.85 M 0.1 Ru 0.05 O 2-ı (M = Si, Fe), as indicated by the H 2 -TPR study. The oxygen storage capacity has been used to correlate surface oxygen reactivity to the CO oxidation activity. Both the compounds reversibly release lattice oxygen and exhibit excellent CO oxidation activity with 99% conversion below 200 ◦ C. A bifunctional reaction mechanism involving CO oxidation by the extraction of lattice oxygen and rejuvenation of oxide vacancy with gas feed O 2 has been used to correlate experimental data. The performance of both the solid solutions has also been investigated for energy application by performing the water gas shift reaction. The present catalysts are highly active and selective towards the hydrogen production and a lack of methanation activity is an important finding of present study. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Materials with high oxygen storage capacity (OSC) have attracted considerable attention due to their wide applications in auto exhaust catalysis, fuel cells and solar cells [1,2]. Ceria and ceria containing materials are promising candidates because of their excellent electrical, catalytic, and mechanical properties [3,4]. Ceria is also a major component of a three way catalyst in automo- tive exhaust emissions [5,6]. The facile Ce 4+ ↔ Ce 3+ redox couple allows these materials to store and release oxygen under oxidizing and reducing conditions, respectively. The performance of these materials as catalyst depends on the OSC and the enhancement in the catalytic activity is directly correlated with increase in the OSC [7–9]. This phenomenon is well established for the reactions such as CO oxidation and water gas shift (WGS) [10–13]. Therefore, it is highly desirable to increase the active oxygen content of ceria based materials for the low temperature CO oxidation, hydrocarbon oxidation, and water gas shift (WGS) reaction. The high OSC and oxygen mobility of ceria can be improved by modifying its structure through the doping of various cations such as Zr, Zn, Co, Cu, and Fe [14–17]. The substitution of Ti and Sn in CeO 2 forming solid solutions also increases the OSC [17–19]. How- ever, the catalytic performance of these materials is poor at low ∗ Corresponding author. Tel.: +91 80 22932321; fax: +91 80 23601310. E-mail addresses: giridhar@chemeng.iisc.ernet.in, giridharmadras@gmail.com (G. Madras). temperatures [2]. In contrast, the Pt group (Pt, Pd, Ru and Rh) metal substituted ceria has showed high CO oxidation activity at low tem- peratures despite their low OSC [20]. The substitution of transition metal such as Cu, Mn, and Fe in CeO 2 results in materials that also exhibit high OSC and these catalysts have the potential to lower the cost [21–23]. The effects of the transition metal substitution on the catalytic performance of ceria have been extensively studied and very high CO oxidation activity was reported in case of Cu modified ceria [24,25]. Due to the stringent environmental regulations, there is an imperative need for more efficient and cost effective catalysts. Therefore, significant efforts has been made to explore materials with high OSC for exhaust gas purification [26]. The substitution of another metal in ceria has attracted considerable interest as a cat- alyst or as a promoter in many catalyst formulations [27]. The size of substituent is one of the key concepts to increase the reducibil- ity and OSC of ceria. The substitution of cation with the smaller (ionic radius) than the Ce cation can create both short and long metal oxygen bonds. The oxygen atoms bonded to the metal with long bonds is weaker and this can increase the reducibility of ceria. This fact is well demonstrated for Ti and Zr-substituted CeO 2 solid solutions [19,28]. Previously, we have observed excellent activ- ity of noble metal modified ceria as three way catalysts [20]. It is widely acknowledged that the aliovalent substitution of metal like Pt, Pd, Cu in CeO 2 lattice induce redox couples in both the substi- tuted metal CeO 2 matrix renders strong metal support interactions [29–31]. Recently, the application of the periodic density func- tional theory (DFT) was used to demonstrate the effect of doping of 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.02.021