Oxidative degradation properties of Co-based catalysts in the presence of ozone M. Gruttadauria a, * , L.F. Liotta b, ** , G. Di Carlo c , G. Pantaleo c , G. Deganello b,c , P. Lo Meo a , C. Aprile d , R. Noto a a Dipartimento di Chimica Organica ‘‘E. Paterno `’’, Universita ` di Palermo, Viale delle Scienze, Parco d’Orleans II, 90128 Palermo, Italy b Istituto per Lo Studio dei Materiali Nanostrutturati (ISMN)-CNR via Ugo La Malfa, 153, 90146 Palermo, Italy c Dipartimento di Chimica Inorganica e Analitica ‘‘Stanislao Cannizzaro’’, Universita ` di Palermo, Viale delle Scienze, Parco d’Orleans II, 90128 Palermo, Italy d Departamento de Quimica, Universidad Politecnica de Valencia, Camino de Vera s/n, E-46022 Valencia, Spain Received 9 January 2007; received in revised form 20 April 2007; accepted 21 April 2007 Available online 29 April 2007 Abstract Four series of cobalt-based catalysts, such as bare Co 3 O 4 and CoO, CoO x –CeO 2 mixed oxides, CoO x supported over alumina and alumina–baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV–visible diffuse reflectance spectroscopy and TG/DT were performed. The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al 2 O 3 –BaO and CoMgAl. The samples Co(1 wt%)/Al 2 O 3 –BaO and Co(1 and 3 wt%)/Al 2 O 3 show a comparable medium activity, while the oxidation properties of bare oxides Co 3 O 4 , CoO and CoO x –CeO 2 are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina–baria look much more stable. The recycle of CoO x /Al 2 O 3 and CoO x /Al 2 O 3 –BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated. On the basis of TPR and UV–visible results it appears that highly dispersed Co 2+ ions especially present over Co(3 wt%)/Al 2 O 3 –BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone. # 2007 Elsevier B.V. All rights reserved. Keywords: Oxidative degradation by ozone; Phenol; Naphtol blue black; CoO x /Al 2 O 3 –BaO; Hydrotalcites 1. Introduction Removing pollutants from industrial process waters and wastewaters is becoming an important area of research as the amount and quality of freshwater available in certain regions of the world continues to decrease due to growing water demands and/or long periods of drought. Moreover, increasingly stricter wastewater discharge standards continue to be introduced worldwide in an effort to reduce the environmental impacts of industrial processes. Nowadays several technologies are available for reclamation of industrial process waters and wastewaters. In the last years, many efforts have been devoted to the heterogeneous wet oxidation [1–4]. Oxidative degradation is a powerful methodology, in this context the oxidizing agent may be H 2 O 2 ,O 2 or O 3 . Ozone, a powerful oxidizing agent (under acidic conditions E(O 3 /O 2 ) = 2.07 V), is effective for the mineraliza- tion of refractory organic compounds. However, it reacts slowly with aromatic organic compounds and, in many cases, it does not cause the complete oxidation. Catalysis combined with the ozonation (oxidation by ozone) process improves the degrada- tion of organic compounds and nowadays finds wide application www.elsevier.com/locate/apcatb Applied Catalysis B: Environmental 75 (2007) 281–289 * Corresponding author. ** Corresponding author. Tel.: +39 091 68 09 371; fax: +39 091 68 09 399. E-mail addresses: mgrutt@unipa.it (M. Gruttadauria), liotta@pa.ismn.cnr.it (L.F. Liotta). 0926-3373/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2007.04.024