Synthesis and thermal treatment of cu-doped goethite: Oxidation of quinoline through heterogeneous fenton process Iara R. Guimaraes a , Amanda Giroto a , Luiz C.A. Oliveira a, *, Mario C. Guerreiro a , Diana Q. Lima b , Jose ´ D. Fabris b a Departamento de Quı´mica, Universidade Federal de Lavras, Caixa Postal 3037, CEP 37200-000, Lavras, MG, Brazil b Departamento de Quı´mica, Universidade Federal de Minas Gerais, CEP 31270-901 Belo Horizonte, MG, Brazil 1. Introduction Goethite (a-FeOOH) structurally consists of double bands of edge-sharing FeO 3 (OH) 3 octahedra. The double bands are linked by corner-sharing in such a way as to form 2  1 octahedra ‘‘tunnels’’ crossed by hydrogen bridges [1]. The yellow-brown goethite occurs in almost all soils and other iron-containing surface formations. Its relative wide availability and suitable physical and chemical properties have allowed consideration of its use as a heterogeneous catalyst or starting material for catalysis of various industrial processes, including NH 3 synthesis, high temperature water–gas shift reaction to produce hydrogen, and desulphurization of natural gas [1]. To achieve the desirable catalytic activity the iron oxide should often be modified, dispersed on a supporting material or doped with some cations. Doping-cations are added to principally assist special redox processes, such as the Fenton reaction. The classical Fenton reaction (Fe 2+ +H 2 O 2 ! Fe 3+ +  OH +  OH), invol- ving hydrogen peroxide and Fe 2+ in solution, is often used to degrade contaminants, such as industrial wastewater textile dyes [2,3]. In order to minimize the amount of the ferric hydroxide sludge forming in the homogeneous reaction, some iron oxides, such as magnetite (ideal formula, Fe 3 O 4 ), hematite (a-Fe 2 O 3 ), goethite (a-FeOOH) or ferrihydrite (Fe 5 HO 8 4H 2 O), are used instead, as heterogeneous catalysts [4]. For this reason, active heterogeneous redox processes are increasingly replacing the homogeneous systems in catalysis research [5–9] and in some technological applications, particularly for environmental remediation. Modifications of the iron oxide structure by doping with isomorphic cations or by thermal treatment have been studied by many authors, in an attempt to improve the catalytic performance of those materials. However, to date, the chemical role of Fe 3+ , Fe 2+ and other ions and their ability to promote the production of the  OH radical are not sufficiently clear [10]. It is well known that nitrogen-containing impurities are significant sources of atmospheric pollution, as well as being potential agents of acid rain. In this context there is a search for new technologies that can better satisfy environmental requirements. In this work, quinoline was used as a model compound present in the diesel fuel, aiming to shed some light on the chemical mechanisms involved in the oxidative reaction. The effect of thermal treatment under a H 2 stream on the surface of goethite and also of copper-doped goethites (Fe 1x Cu x OOH, x = 0.05) on the Fenton oxidation of quinoline was evaluated. 2. Experimental 2.1. Catalyst preparation and characterization All chemicals were high purity grade and were used as purchased. A goethite sample was prepared by co-precipitation, Applied Catalysis B: Environmental 91 (2009) 581–586 ARTICLE INFO Article history: Received 28 March 2009 Received in revised form 19 June 2009 Accepted 26 June 2009 Available online 3 July 2009 Keywords: Goethite Copper Oxidation Fenton-like reaction ABSTRACT Samples of Cu-doped goethites were prepared and characterized by Mo ¨ ssbauer spectroscopy, XRD, TPR and BET surface area measurements. Mo ¨ ssbauer data showed the incorporation of Cu 2+ in the goethite structure, and this cation-doping caused a significant decrease of the chemical reduction temperature in the TPR process. The catalytic behavior of these Fe 1x Cu x OOH materials was investigated for the H 2 O 2 decomposition to O 2 and the Fenton-like reaction to oxidize quinoline. It was observed that Cu 2+ in this goethite and also the thermal treatment with H 2 produced a strong increase in the catalytic activity during the quinoline oxidation. The successive hydroxylation of quinoline during this oxidation strongly suggests that highly reactive hydroxyl radicals are generated during the reaction involving H 2 O 2 on the Cu-goethite grain surface, also confirming that these materials are efficient heterogeneous Fenton catalysts. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +55 35 3829 1626; fax: +55 35 3829 1271. E-mail address: luizoliveira@ufla.br (Luiz C.A. Oliveira). URL: http://www.gqa.dqi.ufla.br Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.06.030