Alumina Supported Fenton-Like Systems for the Catalytic Wet Peroxide Oxidation of Phenol Solutions Carla di Luca, Fernando Ivorra, Paola Massa,* and Rosa Fenoglio INTEMA/Fac. de Ingeniería-Universidad Nac. de Mar del Plata, Juan B. Justo 4302, 7600, Argentina ABSTRACT: Fe 2 O 3 /Al 2 O 3 catalysts (2% Fe) were prepared and characterized by XRD, BET, Raman, and SEM-EDAX. The systems were tested for the catalytic oxidation of phenol solutions (5000 ppm) with H 2 O 2 . The effects of reaction temperature, catalyst loading, phenol initial concentration, and H 2 O 2 :phenol molar ratio were evaluated. The relatively low oxidant consumption rates favored increased mineralization levels at substoichiometric H 2 O 2 initial concentrations. The stability of the catalytic system was improved by means of a thermal treatment at 900 °C, which did not seriously affect the overall reaction performance. ■ INTRODUCTION Hydroxyl radicals have been effectively applied in the field of environmental remediation. Because of their strong oxidizing potential, these species are capable of degrading a wide range of pollutants. Different Advanced Oxidation Processes (AOPs) have been used to generate the •OH radicals. 1-5 Among them, the classic Fenton and Fenton-like reagents (Fe II or Fe III / H 2 O 2 ) remain attractive alternatives for the treatment of nonbiodegradable contaminants, such as phenol. 3,6-8 However, these systems are seriously affected by the typical problems of homogeneous catalysis (separation, regeneration) and also by ineffective consumption of H 2 O 2 and acid-range pH adjustment requirements. 5,8 Thus, different Fenton-like heterogeneous catalysts have been developed by immobilizing transition cations on adequate supports, such as zeolites, pillared clays, silica, activated carbon, or CeO 2 . 8-10 So far, only a few Catalytic Wet Peroxide Oxidation (CWPO) studies have been reported using iron catalysts supported on alumina. 11-18 Al-Hayek and co-workers 15,16 studied the oxidation of phenol solutions over Fe 2 O 3 /Al 2 O 3 powdered catalysts with an iron content of 7.7%. The catalysts were oxidized at 450 °C. The authors used a batch system at room temperature with 100 ppm of phenol as the initial concentration and a molar H 2 O 2 :phenol ratio that was nearly stoichiometric. At these reaction conditions, they observed complete phenol conversion and 60% of mineralization (after 120 min of reaction); leaching levels were moderate, on the order of 10%. More recently, Bautista et al. 18 studied the behavior of a Fe 2 O 3 /Al 2 O 3 powdered catalyst (4% Fe) in the CWPO of aqueous phenol. The catalyst was prepared with a 4% iron content, calcined at 300 °C, and tested in a batch reactor at atmospheric pressure, mild temperatures (25-80 °C), and an initial pH 3. These authors worked at a stoichiometric H 2 O 2 :phenol molar ratio of 14, using different initial concentrations of phenol (100-1500 ppm). For a typical experiment at 50 °C using 100 ppm of phenol as the initial concentration, the phenol conversion was complete, and the mineralization was partial: 27% after 2 h and 60% after 8 h. The levels of leached active phase were low (<2%). By increasing the initial phenol concentration (up to 1500 ppm), they observed a decrease in mineralization levels (42%) and an increased leaching of the iron species (10%). On the basis of these previous reports, we intended to study the performance of alumina-supported catalysts under more demanding reaction conditions, such as more concentrated phenol solutions (5000 ppm). We evaluated the effect of major CWPO variables: reaction temperature, hydrogen peroxide and phenol concentrations, and catalyst mass. The catalysts were prepared in the form of small pellets of Fe 2 O 3 /Al 2 O 3 with low iron content (2% w). We also investigated the impact of using a high calcination temperature (900 °C) in terms of catalyst stability enhancement (for previous reports, calcination temperatures did not exceed 500 °C). ■ EXPERIMENTAL SECTION Catalyst Preparation and Characterization. The Fe 2 O 3 / γ-Al 2 O 3 catalysts were prepared by incipient wetness impregnation of commercial γ-Al 2 O 3 (ALFA AESAR, spherical pellets of 1-1.2 mm) using an aqueous solution of iron citrate (Cicarelli, p.a.) as precursor. After impregnation, the sample was left for 12 h at room temperature and calcined at two different temperatures, 400 and 900 °C, under air current (10 L/min) for 4 h. The catalysts were designed as 2Fe400 and 2Fe900, respectively. The support and the catalysts were characterized using the following techniques: - Surface areas (BET method). Surface areas were calculated from nitrogen adsorption at -196 °C by using a Micromeritics FlowSorb II 2300. - X-ray diffraction (XRD). Powder X-ray diffraction patterns of the catalysts were obtained with a PANalytical X’Pert Pro diffractometer by using nickel-filtered Cu Kα radiation. The patterns were recorder over 10° <2θ < 70° range and compared to the JCPDS files to confirm phase identities. The main peaks corresponding to the Received: February 15, 2012 Revised: June 5, 2012 Accepted: June 11, 2012 Published: June 11, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 8979 dx.doi.org/10.1021/ie300416n | Ind. Eng. Chem. Res. 2012, 51, 8979-8984