Promotion of Rh catalyst interfaced with TiO 2 Elena A. Baranova, Gy€ orgy F oti * , Christos Comninellis Swiss Federal Institute of Technology, SB-ISP-UGEC, CH-1015 Lausanne, Switzerland Received 5 November 2003; received in revised form 17 November 2003; accepted 17 November 2003 Published online: 3 December 2003 Abstract The catalytic activity of Rh for the partial oxidation of methane to syngas can be markedly affected by interfacing polycrystalline Rh films with a dispersed TiO 2 interlayer deposited on YSZ. High CO selectivity (near 97%) can be reached in wide range of CH 4 :O 2 ratio at 550 °C. The observed modification of catalytic activity and selectivity towards CO and H 2 production over Rh interfaced with interlayer of TiO 2 is related to the lowered stability of surface Rh oxide against reduction to metallic Rh. The phenomenon may be interpreted either by electronic type strong metal–support interactions or by self-driven wireless electrochemical promotion mechanism. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Catalyst promotion; Metal–support interactions; Rhodium catalyst; TiO 2 support; Selective methane oxidation 1. Introduction In the last decade, many efforts have been devoted to the catalytic partial oxidation of CH 4 with oxygen to achieve syngas formation according to [1,2]: CH 4 þð1=2ÞO 2 ! CO þ 2H 2 ð1Þ This process has some advantages over the conventional steam reforming, namely: it is more energy efficient and can produce the desired H 2 /CO molar ratio of 2 (instead of 3 in steam reforming) required for methanol or Fischer–Tropsch synthesis. However, this reaction has not been yet developed at industrial scale due to prob- lems related to catalyst deactivation mainly by carbon deposition and/or oxidation of the catalyst to the cor- responding oxide. Prettre et al. [3] were among the first to report for- mation of syngas by the partial oxidation of CH 4 using supported Ni catalyst in the temperature range 973– 1173 K. The reaction was reported to occur in two stages. In the first stage, methane is converted into CO 2 and water until complete conversion of oxygen is achieved according to CH 4 þ 2O 2 ! CO 2 þ 2H 2 O ð2Þ In the second stage, syngas is produced via secondary reactions such as the carbon dioxide and the steam- reforming reaction: CH 4 þ CO 2 ! 2CO þ 2H 2 ð3Þ CH 4 þ H 2 O ! CO þ 3H 2 ð4Þ It is generally agreed that the type of catalyst used can influence strongly the reaction pathway. In fact it has been reported that on Rh catalyst the partial oxidation of methane to CO and H 2 occurs in one step [Eq. (1)] without the formation of CO 2 intermediate [4] as was the case on Ni catalyst [3]. More recent studies have demonstrated that Rh is one of the most promising catalysts in the partial oxi- dation of methane, giving the highest selectivity toward H 2 production [4]. However, the problems related to the Rh catalyst deactivation, mainly due to carbon deposi- tion and/or Rh oxidation to Rh 2 O 3 have not been yet completely resolved. The aim of this work is to investigate the modification of the catalytic activity and stability toward deactivation Electrochemistry Communications 6 (2004) 170–175 www.elsevier.com/locate/elecom * Corresponding author. Tel.: +41-21-693-3673; fax: +41-21-693- 3190. E-mail address: gyorgy.foti@epfl.ch (G. F oti). 1388-2481/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2003.11.009