Low-Pressure Catalytic Wet Air Oxidation of Aniline Over Co 3 O 4 /CeO 2 1 Gu ¨ lin Erso ¨z* and Su ¨ heyda Atalay † Chemical Engineering Department, Faculty of Engineering, Ege UniVersity, 35100 BornoVa, I ˙ zmir, Turkey Low -pressure catalytic wet air oxidation of aniline was investigated in a bubble reactor over Co 3 O 4 (10% wt)/ CeO 2 . The catalyst was prepared by sol-gel technology and characterized by using scanning electron microscope, X-ray diffraction, nitrogen adsorption, and thermogravimetric analysis techniques. The aim was to search for the conditions to destroy the aniline content by avoiding production of byproducts such as ammonium, nitrate, and nitrite ions. The reaction was optimized at 0.5 g/L catalyst loading at 150 °C with a pressure of 4 atm, in 2 h with an air flow rate of 1.36 L/min. A 35.15% amount of aniline was removed, and 14% of the input nitrogen was converted into N 2 gas. To evaluate the stability of the catalyst, two consecutive runs were performed by reusing the catalyst recovered. The highest removal with the reused catalyst was found as 34.94%, showing that Co 3 O 4 /CeO 2 is a stable catalyst. 1. Introduction Aromatic amines such as aniline are known to be toxic and hazardous water pollutants. They are present in several types of wastewaters including those from textile, petroleum, paper, and the coal industry and are widely used in the manufacturing of rubbers and plastics, azo dyes, agrochemicals, pharmaceu- ticals, and pesticides. They are known to be toxic water pollutants, and their presence in wastewater even in very low concentrations is harmful to aquatic life. 1 Aromatic amines therefore must be treated in order to meet the specifications for discharge. The treatment of these kinds of organic wastes, by biological processes, is often unsuitable due to their inherent toxicity to microorganisms. The use of traditional noncatalytic chemical processes or incineration may be too costly and energy intensive. 2 Recent literature shows that, among the wastewater treatment techniques, catalytic wet air oxidation (CWAO) of organic wastes in water seems to be effective and promising. 2-6 The wet air oxidation (WAO) process has well-known capabilities for breaking down biologically refractory com- pounds to simpler, easily treated materials, before they are released into the environment. In general, this aqueous-phase flameless combustion process takes place at high reaction temperatures (473-593 K) and pressures (20-200 bar) by means of an active oxygen species. 7 The use of catalysts in WAO not only makes it possible to reduce the reaction temperature and pressure and to increase oxidation rates but also avoids the formation of harmful products by complete oxidation of organic contaminants to harmless carbon dioxide, water, and nitrogen. 8,9 Indeed, in the past decades, numerous authors have demon- strated CWAO efficiency with a large range of compounds such as carboxylic acids, aromatics, polymers, N- and O-containing organic compounds, and treatment of toxic nitrogen-containing compounds as one of the major applications of the CWAO processes. 10 The different steps of the CWAO of nitrogen-containing compounds, involved in the process, can be summarized in Scheme 1. 11 Consequently, to evaluate the total process efficiency, it is essential to know the production of byproducts such as ammonia, nitrogen, nitrates, and nitrites. The desired product is molecular nitrogen. In literature there are valuable studies performed on CWAO of various industrial wastes. 10-13 Nevertheless, the reaction conditions of CWAO are still somewhat severe, and the search for an active and durable catalyst has become the focus of investigations. Though some inspiring results have been reported, it is still necessary to develop more active, stable, and environmentally friendly catalysts. In this research the main aim was to study the effectiveness of the WAO of aqueous aniline over the prepared nanostructured catalyst to make the stream ecofriendly by minimizing the organic content and also minimizing byproducts such as ammonium, nitrate, and nitrite ions by selectively converting the N atom in aniline into N 2 gas by searching for the suitable conditions. 2. Experimental Section 2.1. Catalyst Preparation. Co 3 O 4 /CeO 2 particles were pre- pared by the sol-gel method as reported in literature. 14-16 The procedure is mainly based on two steps. First, CeO 2 support was prepared by sol-gel technology, and then it was impreg- nated with Co 3 O 4 by the incipient wetness impregnation method. 2.2. Catalyst Characterization. The surface morphology of the catalyst prepared was investigated using a scanning electron microscope (SEM) analyzer (Phillips XL_30S FEG). Their phases were analyzed with powder X-ray diffraction (Phillips X’Pert Pro X-ray diffraction). In addition to these the charac- terization was enriched by nitrogen adsorption (Quantachrome 1 * To whom correspondence should be addressed. Tel.: 00 90 232 3884000/3061. Fax: 00 90 232 3887776. E-mail: gulin.aytimur@ ege.edu.tr. † Tel.: 00 90 2323887600. Fax: 00 90 2323887776. E-mail: suheyda.atalay@ ege.edu.tr. Scheme 1. CWAO of Nitrogen-Containing Compounds Ind. Eng. Chem. Res. 2010, 49, 1625–1630 1625 10.1021/ie901383e  2010 American Chemical Society Published on Web 01/15/2010