Catalytic wet oxidations of aromatic compounds over supported copper oxides Ayumu Onda Æ Yotaro Suzuki Æ Shinji Takemasa Æ Koji Kajiyoshi Æ Kazumichi Yanagisawa Received: 26 October 2006 / Accepted: 25 March 2008 / Published online: 9 April 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Catalytic wet oxidations of naphthalene as a model compound of persistent aromatic compounds were carried out with hydrogen peroxide in a closed autoclave lined with Teflon. CuO/Al 2 O 3 and CuO/AC catalyst showed the high activity for the naphthalene oxidation with hydrogen peroxide of 1.0 mol L -1 at 100 °C. Naphthalene, whose initial concentration was 1.0 g L -1 , was converted completely and the concentration of water-soluble organic compounds in the resultant aqueous solution was less than 25 ppm-C. In contrast, platinum, and manganese oxide, silver oxide, and ruthenium oxide catalysts consumed hydrogen peroxide preferentially. Iron and nickel oxides catalysts showed lower activity than the copper oxide catalyst. During the reaction, the intermediate organic acids were formed and then were oxidized. Simultaneously, copper species of CuO catalysts were dissolved and then were precipitated. The precipitated copper species on the catalyst support showed the catalytic activity. CuO/Al 2 O 3 catalysts showed high activity for the six successive batch reactions with the treatment of sodium carbonate after the reaction to precipitate copper ions. Introduction Wet oxidation with oxygen or hydrogen peroxide as a oxidizing agent has attracted great attention because of its potential applications to decompose and dechlorinate persistent chlorinated organic compounds [1–3], and to purify wastewater containing organic pollutant [4–10]. Phenol is a represented model compound of persistent organic pollutants for wet oxidation studies. Many studies for the catalytic wet oxidation of phenol were reported [4– 8, 11–15]. Among many heterogenous catalysts, catalysts based on copper oxides show high activities in the oxida- tion and are commonly used to study the catalytic wet oxidation of wastewater containing persistent organic pol- lutant [11]. The copper oxide catalysts show deactivation during the oxidation due to the leaching of copper caused by the exposure of the catalyst to acid aqueous solution [15]. It is difficult to avoid the acid conditions since the final intermediates formed through the oxidation of organic pollutants are short chain acid such as oxalic, formic, and acetic acid. Naphthalene and its polymers are used as a stabilizing and protecting material of hazardous substances. Disposal of these materials is a problem because naphthalene is a persistent organic compound. Catalytic and non-catalytic oxidations of naphthalene were investigated for the steam reforming of tar in gas phase [16, 17] and for the elimi- nations of polycyclic aromatic hydrocarbons (PAHs) with oxygen gas in gas phase [18–20] and in supercritical water [21] and with ozone gas at ordinary temperature [22, 23]. In those studies, naphthalene was used as a model com- pound of tar derived from biomass gasification and PAHs which are environmental pollutants in the exhausts of the diesel vehicles with particulates. The total oxidation of naphthalene with oxygen gas was effectively controlled by heterogeneous catalysts such as platinum supported on alumina [19]. Although naphthalene is known as a water-insoluble compound, the solubility exponentially increases with increasing temperature, such as 28 ppm at 293 K, 61 ppm A. Onda (&) Á Y. Suzuki Á S. Takemasa Á K. Kajiyoshi Á K. Yanagisawa Research Laboratory of Hydrothermal Laboratory, Kochi University, Kochi 780-8520, Japan e-mail: onda@cc.kochi-u.ac.jp 123 J Mater Sci (2008) 43:4230–4235 DOI 10.1007/s10853-008-2612-3