Platinum catalysts supported on MWNT for catalytic wet air oxidation of nitrogen containing compounds J. Garcia a,b , H.T. Gomes a , P. Serp c , P. Kalck c , J.L. Figueiredo a , J.L. Faria a, * a Laborato ´rio de Cata ´lise e Materiais, Departamento de Engenharia Quı ´mica, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal b Departamento de Ingenierı ´a Quı ´mica, Facultad de Ciencias, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain c Laboratoire de Catalyse, Chimie Fine et Polyme `res, Ecole Nationale Supe ´rieure des Inge ´nieurs en Arts Chimiques et Technologiques, 118 route de Narbonne, 31077 Toulouse Cedex 4, France Available online 25 March 2005 Abstract Multi-walled carbon nanotubes (MWNT) activated by nitric acid oxidation were used to prepare supported platinum (1% Pt) catalysts by the excess solution impregnation method. Three different platinum precursors were used to prepare the impregnation solutions, namely diiodo dicarbonyl platinum(II) [PtI 2 (CO) 2 ], dimethyl (1,5-cyclooctadiene) platinum(II) [Pt(CH 3 ) 2 (C 8 H 12 )] and hydrogen hexachloroplatinate(IV) hexahydrate H 2 PtCl 6 Á6H 2 O. The catalysts were characterized by transmission electron microscopy (TEM) analysis and H 2 chemisorption. They were tested in the catalytic wet air oxidation (CWAO) of aniline aqueous solutions (200 8C and 6.9 bar of oxygen partial pressure). The Pt/MWNT catalyst prepared from H 2 PtCl 6 Á6H 2 O showed the best performance with respect to combined activity and selectivity for aniline conversion to non-organic compounds. This catalyst was used in CWAO (150 8C and 6.9 bar of oxygen partial pressure) of aqueous solutions of various textile dyes such as the monoazo dye chromotrop 2R (C2R), the diazo dye erionyl red B (ERB) and the triazo dye solophenyl green BLE (SG) 155%. It was found that the selectivity for dye removal decreased in the order diazo > monoazo > triazo. The CWAO of a textile wastewater was also performed using the same catalyst and identical reaction conditions. Complete color removal and 51.2% TOC abatement was obtained under these conditions. # 2005 Elsevier B.V. All rights reserved. Keywords: Catalytic wet air oxidation; Platinum; Multi-walled carbon nanotubes; Wastewaters; Azo dyes 1. Introduction Since their discovery [1] carbon nanotubes (CNT) have attracted great interest from both fundamental and applied standpoints. Following this interest, large-scale syntheses facilities are currently being established by several research laboratories [2,3]. Carbon nanotubes are examples of materials with a broad range of potential applications owing to their high mechanical and unique electrical properties [4]. These properties are also interesting when considering CNT as a support for preparing heterogeneous catalysts, especially for catalysts to be employed in liquid-phase reactions. The results published to date seem to indicate that nanostructured carbon can represent a new class of advanced materials for catalytic applications leading to more efficient and highly selective processes, therefore environmentally more benign [5–7]. Carbon nanotubes can be multi-walled, double-walled or single-walled, depending on the number (several, two or one, respectively) of graphitic layers [8]. In this work, we aimed at the preparation of platinum catalysts supported on multi-walled carbon nanotubes (MWNT) for the catalytic wet air oxidation (CWAO) of aqueous solutions with nitrogen containing pollutants (including model solutions of aniline or azo dyes) and textile wastewaters. CWAO is a known process for oxidative treatment of industrial wastewaters, due to its intrinsic efficiency in the elimination of chemical oxygen demanding species, by means of an oxidizing source under relatively mild conditions (125–220 8C, 5–50 bar) in the presence of an www.elsevier.com/locate/cattod Catalysis Today 102–103 (2005) 101–109 * Corresponding author. Tel.: +351 225 081 645; fax: +351 225 081 449. E-mail address: jlfaria@fe.up.pt (J.L. Faria). 0920-5861/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2005.02.013