Near ambient pressure XPS investigation of the interaction of ethanol with Co/CeO 2 (111) L. Óvári a,1 , S. Krick Calderon b,1 , Y. Lykhach b , J. Libuda b , A. Erd } ohelyi c , C. Papp b,⇑ , J. Kiss a,c , H.-P. Steinrück b a MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, H-6720 Szeged, Rerrich Béla tér 1, Hungary b Lehrstuhl für Physikalische Chemie II, University of Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany c Department of Physical Chemistry and Materials Science, University of Szeged, H-6720 Szeged, Aradi vértanúk tere 1, Hungary article info Article history: Received 20 March 2013 Revised 13 July 2013 Accepted 16 July 2013 Keywords: Ethanol steam reforming Near ambient pressure XPS Cobalt Ceria abstract Near ambient pressure X-ray photoelectron spectroscopy was applied to study the interaction of ethanol (CH 3 CH 2 OH) with a well-ordered CeO 2 (111) film on Cu(111) and with a Co/CeO 2 (1 1 1)/Cu(1 1 1) model catalyst. The oxidation state of the surface and the chemical nature of reaction intermediates were ana- lyzed. At 300 K, the oxidation state of ceria decreased gradually with increasing ethanol pressure. At a constant pressure of 0.1 mbar, the reduction of Ce 4+ to Ce 3+ increased significantly between 320 and 600 K due to a higher mobility of oxygen or Ce 3+ centers at elevated temperatures. The main intermedi- ate, ethoxide, was formed by dissociative adsorption of ethanol at room temperature. No coke formation was observed up to 600 K on CeO 2 . Upon deposition of metallic cobalt, partial reduction of ceria was observed, leading to the formation of Co 2+ sites but still leaving metallic Co in the metal particles. During the reaction of ethanol with the Co/CeO 2 (1 1 1) model catalyst, the amount of Co 2+ decreased drastically with increasing temperature, and at 600 K, the majority of Co was metallic. This process was accompa- nied by the severe reduction of ceria and the formation of significant carbon deposits. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Ethanol obtained by the fermentation of agricultural wastes can be an important carbon-neutral renewable energy source and also a renewable raw material for chemical industry. Great efforts are currently undertaken to produce hydrogen by heterogeneously catalyzed processes from these renewable sources. Hydrogen has potential applications as energy carrier to be used in fuel cells or in large-scale processes like ammonia synthesis. This demand in- spired studies of the dehydrogenation of oxygenated hydrocar- bons, especially ethanol [1–4]. The steam reforming of ethanol (SRE), the partial oxidation of ethanol (POX), and the oxidative steam reforming (OSR) are currently in the focus of catalytic re- search as potential candidates for H 2 production [4]. One advan- tage of bio-derived ethanol is its low sulfur content, reducing the poisoning of catalysts, and its low toxicity as compared to metha- nol. Furthermore, ethanol from bio sources contains water and thus is particularly well suited for steam reforming, since the dis- tillation step to produce pure ethanol can be omitted. During the steam reforming of ethanol, acidic supports like Al 2 O 3 favor dehydration and thereby increase the tendency for coke formation due to the polymerization of ethylene [5]. How- ever, on ceria (CeO 2 ), which is considered to be a basic support, dehydration is limited and its redox properties hinder coke forma- tion. Additionally, ceria promotes the water–gas-shift (WGS) reac- tion [6,7]. Noble metals, especially Rh, proved to be excellent catalysts for the reaction, but their price is prohibitively high. As an alternative to expensive transition metals, Co is considered a promising catalyst for the reaction [7–9]. Co achieves a high etha- nol conversion and selectivities of over 90% for H 2 and CO 2 on CeO 2 and also on other supports, even at relatively low temperatures (723 K) [10,11]. Supported Co catalysts break the C–C bond in ad- sorbed ethanol [12]. It was found that addition of a CeO 2 promoter to the unsupported Co powder catalyst stabilizes the more active hcp structure of Co and hinders sintering during SRE [13]. Surface science studies on adsorption of alcohols on group VIIIB and IB transition metal surfaces, performed in ultrahigh vacuum (UHV), were reviewed by Mavrikakis and Barteau [14]. Depending on the particular metal, dehydrogenation and C–C bond scission lead to the formation of alkoxide, oxametallacycle, aldehyde, acyl, and coke on the surface and mostly H 2 , CH 4 , CO, and aldehyde in the gas phase. The rupture of the C–C bond generally requires high- er activation energy than the scission of C–H and O–H bonds. C–O 0021-9517/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcat.2013.07.015 ⇑ Corresponding author. E-mail address: christian.papp@chemie.uni-erlangen.de (C. Papp). 1 Shared first authors. Journal of Catalysis 307 (2013) 132–139 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat