Electrochimica Acta 49 (2004) 879–885 Electrocatalytic activity of surface adsorbed ruthenium–alizarin complexone toward the oxidation of benzyl alcohol Aldaléa Lopes Brandes Marques ∗ , Weihua Li 1 , Edmar Pereira Marques, Jiujun Zhang Departament of Technology Chemistry, Universidade Federal do Maranhão, Av. dos Portugueses, S/N 65.080-040 São Lu´ ıs, MA, Brazil Received 27 May 2003; received in revised form 10 July 2003; accepted 19 September 2003 Abstract The surface electrochemical behavior of an adsorbed alizarin complexone (abbreviated as AC) and its surface coordination with Ru(II) were studied in aqueous solution at a pH range of 0–6. The surface complex of ruthenium with AC displays strong electrocatalytic activities toward benzyl alcohol. Based on the rotating disk electrode measurement, it is believed that the electrocatalytic oxidation of benzyl alcohol is a two-electron and two-proton process with benzaldehyde as a major product. On the other hand, ruthenium–AC surface complex has also shown catalytic activities toward electro-oxidation of several small organic molecules such as methanol, formic acid, formaldehyde, ethanol, and acetaldehyde. © 2003 Elsevier Ltd. All rights reserved. Keywords: Ruthenium; Alizarin complexone; Electrocatalysis; Benzyl alcohol; Methanol; Ethanol 1. Introduction The electrocatalytic oxidation of small organic molecules such as methanol, ethanol, benzyl alcohol and others has been of interest as potential fuel reactions in fuel cells [1–3] and other industries [4] for many years. The electrocatalytic oxidation of benzyl alcohol (abbrevi- ated as BA), which is one of the representative primary alcohols, was investigated by several research groups [4–10]. Among those surface catalysts explored, ruthe- nium oxides and its complexes have been found to be active towards the electrocatalytic oxidation of BA [5–7]. Wong et al. [5] has reported the electrocatalytic activity of three mono complexes, trans-[Ru(V)(TMC)O(Cl)] 2+ , trans-[Ru(V)(TMC)O(NCO)] 2+ and trans-[Ru(V)(TMC)O- (N 3 )] 2+ towards BA oxidation in a non aqueous solution (acetonitrile media). Here, TMC is 1,4,8,11-tetramethyl-1,- 4,8,11-tetraazcyclotetradecane. The electrochemical behav- iors of these complexes were examined on a glass carbon electrode. The detail kinetics of such electrocatalyzed BA ∗ Corresponding author. Tel.: +55-98-217-8299; fax: +55-98-217-8245. E-mail address: aldalea@ufma.br (A.L.B. Marques). 1 Present address: Department of Chemistry and Biology, Suzhou Teacher’s College, Suzhou City, Anhui, PR China. oxidation was also investigated. Shi and Anson [6] have prepared a surface ruthenium oxide, [Ru 4 (OH) 12 ] 4+ , on a graphite electrode by Ru(II) in situ oxidation, and found its electrocatalytic activity towards BA oxidation in aqueous solution as well. A multiple layer of catalyst containing [P 2 Mo 18 O 62 ]6– and Ru(II)–polypyridine complex was ex- plored for BA electro-oxidation by Kloster and Anson [7]. The exploration for a new catalyst for primary alcohol oxidation is continuously an attractive subject in many ap- plications. We have found that Ru(II)–alizarin complexone displays an electrocatalytic activity towards the oxidation of several primary alcohols, especially BA. This new surface complex of ruthenium(II)–alizarin complexone is abbrevi- ated as [Ru II (AC)(H 2 O) 2 ] - in this paper. The proposed [Ru II (AC)(H 2 O) 2 ] - structure is shown in Fig. 1b. In the molecular structure of alizarin complexone ligand (abbreviated as AC) (Fig. 1a) [11], two functional groups are obvious. The first group is the big conjugated benzenoid ring which could provide a strong affinity to the graphite electrode surface, resulting in an AC modified elec- trode surface. The second group is a four-coordinate chelat- ing environment with two acetic acid group, one 2-hydroxyl group, and the nitrogen atom, which can bind metal ions at the electrode surface. In this way, if a ligand is adsorbed on a graphite electrode surface, it will have ability to pick-up metal ions to form surface complex. Thus the formed surface 0013-4686/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2003.09.040