Journal of Hazardous Materials 177 (2010) 407–413 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Total oxidation of toluene over calcined trimetallic hydrotalcites type catalysts Luz A. Palacio a,b , Juliana Velásquez b , Adriana Echavarría b , Arnaldo Faro c , F. Ramôa Ribeiro a , M. Filipa Ribeiro a,∗ a Instituto Superior Técnico, IBB - Centro de Engenharia Biológica e Química, Universidade Tecnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b Grupo Catalizadores y Adsorbentes, Universidad de Antioquia 1-317, A.A. 1226 Medellín, Colombia c Departamento de Fisicoquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Ilha do Fundão, CT bloco A, Rio de Janeiro, Brazil article info Article history: Received 4 June 2009 Received in revised form 7 December 2009 Accepted 8 December 2009 Available online 16 December 2009 Keywords: Hydrotalcite Toluene Combustion VOCs abstract Two trimetallic ZnCuAl and MnCuAl hydrotalcites have been successfully synthesized by a co- precipitation method. The manganese based material was identified as a new hydrotalcite phase. Both lamellar precursors were calcined at 450 and 600 ◦ C and the resulting catalysts were tested on reaction of total oxidation of toluene. The solids were characterized by X-ray diffraction, thermal analysis, atomic absorption spectroscopy, Fourier transformed infrared spectroscopy, N 2 adsorption and H 2 temperature- programmed reduction. It was found that ZnCuAl materials are composed of copper and zinc oxides supported on alumina; while MnCuAl ones comprise basically spinel phases, which were not completely identified. The catalytic behavior of the calcined samples showed that Mn hydrotalcite calcined at 450 ◦ C exhibited the best catalytic performance that corresponds to 100% toluene conversion into CO 2 at about 300 ◦ C. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The layered double hydroxides (LDHs) or hydrotalcite-like materials have been widely investigated owing to their potential applications as ion exchangers, adsorbents, ionic conductors, cat- alysts and catalyst precursors, supports, pharmaceuticals and so on [1]. The general chemical formula of these lamellar solids can be written as [M 2+ 1-x M 3+ x (OH) 2 ](A n- ) x/n · mH 2 O where M 2+ and M 3+ are divalent and trivalent cations (Mg 2+ and Al 3+ in the natural hydro- talcite) that occupy the center of M(OH) 6 octahedral units and A n- is a compensation anion [2]. A large number of LDHs with a wide variety of M(II)–M(III) cation pairs, as well as different anions in the interlayer have been reported in the scientific literature as stated in reviews like those from Sels et al. and Crepaldi et al. [3,4]. However, LDHs totally replacing the Mg 2+ for transition metals in the brucite-like layer are scarce due to the difficulty in obtaining a pure hydrotalcite phase. An outstanding factor that increases the effort for the synthesis of these materials is that thermal decomposition of LDHs precursors leads to the formation of M 2+ and M 3+ mixed oxides exhibiting fine dispersion of metal cations and high surface area, compared with those obtained from direct methods; besides memory effect, good thermal stability and good mixed oxides homogeneity are other properties of this type of materials [5]. ∗ Corresponding author. Tel.: +351 21 841 78 72; fax: +351 21 841 91 98. E-mail address: filipa.ribeiro@ist.utl.pt (M.F. Ribeiro). The mixed oxides obtained from hydrotalcites have shown a very good performance in many reactions of industrial interest like CH 4 and methanol reforming [6,7], hydrodesulfurization of gasoline [8], removal of SO 2 and NO x [9] and also for catalytic combustion of VOCs [10–12]. Volatile organic compounds (VOCs) are dangerous air pollutants that can be converted by catalytic combustion, which represents a very promising alternative for their elimination, due to the energy saving that it can provide comparatively to thermal combustion and also because transition metal based oxides can replace traditional noble metal based catalysts, because of their low cost and stability [13]. Recently, some hydrotalcites have been reported as precur- sors for obtaining catalysts for VOCs elimination, mainly toluene. They exhibit promising results, but combustion temperatures are not lower than those observed with noble metal catalysts. The tested hydrotalcites are based on the systems Cu–Mg–Al [10], Co–Mn–Al [14], Mg–Mn–Al [12], Cu(Zn)–Mn(Al) [15] for toluene combustion and Ni–Al for toluene and ethanol combustion [16]. In this work, hydrotalcite-like materials have been used as cat- alyst precursors, and their catalytic behavior was evaluated in toluene combustion. MnCuAl and ZnCuAl trimetallic hydrotalcites were synthesized and calcined. The first one evidences a new composition with hydrotalcite structure that differs from the one reported by Zimowska et al. [15] in terms of composition of the LDH and structure of the calcined material. Toluene was selected as VOC model molecule because it is a commonly used solvent in 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.12.048