Applied Catalysis B: Environmental 150–151 (2014) 402–410 Contents lists available at ScienceDirect Applied Catalysis B: Environmental jo ur nal home p ag e: www.elsevier.com/locate/apcatb Wet Air Oxidation of phenol over Pt and Ru catalysts supported on cerium-based oxides: Resistance to fouling and kinetic modelling Sylvain Keav a,b,∗ , Alejandra Espinosa de los Monteros b , Jacques Barbier Jr. b , Daniel Duprez b a Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Solid State Chemistry and Catalysis, Ueberlandstrasse 129, CH-8600 Dübendorf, Switzerland b IC2MP, UMR 7285, University of Poitiers and CNRS, 4 rue Michel Brunet, 86022 Poitiers Cedex, France a r t i c l e i n f o Article history: Received 1 October 2013 Received in revised form 13 December 2013 Accepted 16 December 2013 Available online 24 December 2013 Keywords: CWAO Phenol Noble metal OSC Deactivation a b s t r a c t Ceria and doped ceria supported Pt and Ru catalysts were tested at 160 ◦ C in the Catalytic Wet Air Oxida- tion (CWAO) of phenol. Catalysts were compared in terms of activity, selectivity and resistance towards fouling. The respective influences of metal phase and support were studied. Under the selected oper- ating conditions, 100% phenol conversion could be reached. Contrary to what was expected, improved Oxygen Storage Capacities (OSC) accelerated the accumulation of adsorbed species on the catalyst sur- face, therefore limiting the catalytic performance. By contrast, high metal dispersions enhanced both the elimination of aqueous organic compounds and the degradation of heavy molecules involved in the cat- alyst fouling. The progressive decrease in activity induced by carbonaceous deposits could be kinetically modelled using a simple reaction scheme. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Known since the early 20th century, the Wet Air Oxida- tion (WAO) process is particularly promising for the treatment of wastewaters containing highly concentrated, toxic or hardly biodegradable compounds [1]. WAO consists in oxidizing organic pollutants into nontoxic products (ultimately CO 2 and H 2 O). In the absence of a catalyst, temperatures up to 320 ◦ C and pressures up to 200 bar are necessary to attain acceptable conversions. The use of a catalyst significantly improves the efficiency of the process: Cat- alytic Wet Air Oxidation (CWAO) can be operated at temperatures and pressures below 200 ◦ C and 30 bar, respectively. Many heterogeneous catalytic systems have been considered for the reaction. Amongst them, supported Pt, Ru and Pd noble metals demonstrate high stability and activity. Due to their efficiency in processes involving redox reactions as well as their stability under acidic and oxidative conditions, cerium-based oxides are excellent candidates as supports for WAO catalysts. It was shown that ceria alone is able to convert more than 90% of aqueous phenol [2] and ∗ Corresponding author at: Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Solid State Chemistry and Catalysis, Ueberland- strasse 129, CH-8600 Dübendorf, Switzerland. Tel.: +41 587 654 726. E-mail address: sylvain.keav@empa.ch (S. Keav). that its addition to certain formulations can greatly improve the catalytic performance [3]. Additionally, some cerium-based oxides, such as MnO 2 –CeO 2 , are extremely active in the oxidation of refrac- tory compounds [4]. The efficiency of such catalytic systems comes from the oxygen transfer and storage properties of ceria, which result from the ability of Ce element to easily switch between +III and +IV oxidation states. The mobility of oxygen atoms can be improved by heat treatment, doping or the presence of noble metal species dispersed on the oxide surface [2,5]. Phenol is an intermediate in the oxidation of many aromatic compounds. Moreover, it is a toxic molecule resistant to biotreat- ment. Several authors determined the reaction pathway of the catalytic oxidation of aqueous phenol [6–8]. One of the most elabo- rated models, proposed by Rivas et al. [9], was based on elementary radical reactions (phenol oxidation is recognized to proceed via a free-radical mechanism [10]). The authors calculated unknown rate constants and verified that predicted concentration profiles were in agreement with experimental data. Eftaxias et al. [11] carried out a noteworthy kinetic study of phenol oxidation: a scheme comprising 7 reactions was considered and 31 parameters were simultane- ously optimized. However, these reaction pathways do not take into account the formation of deactivating polymeric species. A few counterexamples can be found. Alejandre et al. [12] considered the direct polymerization of phenol. Masende et al. [13] proposed a particularly interesting scheme in which they specified desired and 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.12.028