Electrochemically enhanced metal-support interaction of highly dispersed Ru nanoparticles with a CeO 2 support H.A.E. Dole a , L.F. Safady a , S. Ntais a , M. Couillard b , E.A. Baranova a,⇑ a Department of Chemical and Biological Engineering, Center for Catalysis Research and Innovation (CCRI), University of Ottawa, 161 Louis-Pasteur St., Ottawa, ON K1N 6N5, Canada b National Research Council Canada, 1200 Montreal Road, Ottawa, ON K1A 0R6, Canada article info Article history: Received 30 January 2014 Revised 4 June 2014 Accepted 4 July 2014 Keywords: Ru nanoparticle Thermally-decomposed Ru Ceria Yttria-stabilized zirconia Electrochemical promotion Ethylene oxidation Metal-support interaction abstract Small particle size (1.1 nm) Ru nanoparticles were supported on a mixed ionic-electronic conductor, CeO 2 , with a low metal loading (1 wt%), interfaced with a YSZ electrolyte. A pronounced enhancement (up to about 2.5 times) of the catalytic rate for the complete oxidation of ethylene was observed for neg- ative polarization. The opposite effect was observed for positive polarization. Apparent Faradaic efficien- cies up to 96 were determined, indicating a non-Faradaic effect. The modification of the cerium oxidation state (i.e., reduction from Ce 4+ to Ce 3+ ) is proposed to enhance the catalytic performance of the Ru nano- particles. XPS analysis was performed to confirm this reduction of ceria. The enhancement of catalytic activity is attributed to the presence of more oxygen vacancies in the ceria interlayer causing a stronger metal-support interaction. Results demonstrate the feasibility of in-situ modification of the metal sup- port-interaction between Ru nanoparticles and CeO 2 catalytic support by a small current (2 lA) application. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Electrochemical promotion of catalysis (EPOC) is a promising method for enhancing catalytic activity through the application of a small electrical stimulus between the catalyst-working and counter electrode deposited on a solid electrolyte [1–3]. The elec- tronic properties of the catalyst can be modified resulting in a change in catalytic activity. In the case of yttria-stabilized zirconia (YSZ) as a solid electrolyte, the addition or removal of O 2 species on the catalyst surface can be controlled in situ depending on the specified reaction conditions. Fully reversible and ‘‘permanent’’ or ‘‘persistent’’ EPOC has been reported for more than 70 various cat- alytic systems [1]. In reversible EPOC experiments, the reaction rate returns to its initial value after the electrical stimulus is inter- rupted. For permanent EPOC (P-EPOC), the reaction rate remains at a higher value than the initial open circuit value [4,5]. Despite receiving much attention, this phenomenon has not yet reached commercial application. One of the main technical factors prevent- ing such development is the use of thick film catalysts with low surface areas and high material costs [6]. The first step towards an alternative cell to accommodate high surface area catalysts was pioneered by Marwood, in the 1990s, where it was proposed that EPOC could be achieved through an isolated catalyst surrounded by two gold electrodes between which current passed [7,8]. Since then, several studies have expanded on this idea of a bipolar configuration, for example, sputtering a Pt catalyst between a comb-like gold electrode configuration [9,10]. Kambolis et al. [11] also demonstrated the feasibility of electropromoting a highly dispersed (15%), Pt nanoparticle (average size: 8 nm) cat- alyst for the oxidation of propane. A 38% enhancement of the cat- alytic rate was observed with apparent Faradaic efficiency values up to 85. Ceria (CeO 2 ) is a mixed ionic-electronic conducting (MIEC) material that conducts O 2 ions due to oxygen vacancies in the crystallographic structure in addition to conducting electrons at elevated temperatures. Furthermore, due to its non-stoichiometry, CeO 2 has the ability to undergo conversion between Ce 4+ and Ce 3+ quite easily [12]. These properties make the use of ceria-containing catalysts of interest for many applications, including soot removal from diesel engine exhaust [13], catalyst additives in combustion processes [14], and as a solid oxide electrolyte for fuel cells [15]. In heterogeneous catalysis, Pt group metals deposited on CeO 2 show a metal-support interaction (MSI) effect associated with charge transfer between the two solids that are in contact [16–18]. In EPOC studies, using a MIEC can also ensure electrical connectivity between highly dispersed nanoparticle catalysts [11]. EPOC studies using CeO 2 as an interlayer include those performed by Jiménez-Borja et al. [19,20] that compared both Pd/YSZ and Pd/CeO 2 /YSZ electrocatalytic systems for the oxidation http://dx.doi.org/10.1016/j.jcat.2014.07.003 0021-9517/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Fax: +1 6135625172. E-mail address: elena.baranova@uottawa.ca (E.A. Baranova). Journal of Catalysis 318 (2014) 85–94 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat