Chemical Engineering Science 63 (2008) 5056 – 5065 www.elsevier.com/locate/ces Novel oxidation reaction at ambient temperature and atmospheric pressure with electric discharge and oxide surface Yasushi Sekine a , ∗ , Shinjiro Asai a , Shigeru Kado b , Masahiko Matsukata a , Eiichi Kikuchi a a Department of Applied Chemistry, School of Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan b Department of Mechanical and Control Engineering, Tokyo Institute of Technology, School of Science and Engineering, 152-8552, Japan Received 16 May 2007; received in revised form 29 November 2007; accepted 13 December 2007 Available online 30 January 2008 Abstract We investigated a novel oxidation reaction with surface-oxygen and lattice-oxygen induced using a non-equilibrium electric discharge at ambient temperature. We employed MgO, ZrO 2 , and TiO 2 for this novel reaction. Methane was oxidized easily and converted into H 2 , CO, and CO 2 by the surface-oxygen and lattice-oxygen of oxide with activation of discharge at ambient temperature without gas-phase oxygen. The oxide itself was stable after the reaction. Among these oxides, the tetragonal phase and amorphous phase of ZrO 2 showed remarkably high activity for methane oxidation. Consequently, up to 8% of surface and lattice oxygen of the oxide was consumed by methane oxidation induced by electric discharge. The non-equilibrium electric discharge activated both the surface-oxygen and the lattice-oxygen of the oxides and methane molecules in the gas phase. After these reactions, the oxide surface vacant sites were recovered partially through steam post-treatment. Hydrogen formed simultaneously with steam decomposition. Other reactions were also studied by changing the reaction gas: methane into carbon monoxide, carbon monoxide with oxygen, and carbon monoxide with steam. Furthermore, the correlation of reactivity between the feed gas and surface oxygen was studied. Emission spectra under a CH 4 atmosphere with electric discharge showed complex peaks caused by carbon monoxide formation at 280–500 nm at 0–4 min, suggesting that surface oxygen on oxides was probably consumed within 4 min from the start of the reaction.  2007 Elsevier Ltd. All rights reserved. Keywords: Electric discharge; Reaction at ambient temperature; Oxide surface; Methane oxidation 1. Introduction Numerous investigations of plasma-catalysis hybrid systems have been reported in recent years, with a catalyst to control product selectivity and/or conversion (Hammer et al., 2004; Heintze and Pietruszka, 2004; Kraus et al., 2001; Nozaki et al., 2004; Onoe et al., 2004; Pietruszka et al., 2004, etc.). We have reported that a hybrid system of non-equilibrium spark dis- charge and a Lindlar catalyst (Pd.CaCO 3 with Pb) showed high throughput synthesis of ethylene from methane at temperatures as low as 293–373 K with atmospheric pressure (Kado et al., 2003, 2004). Its one-pass yield was as high as 47%, which is re- markably high among precedent reports for the direct formation of ethylene from methane. To date, the roles of the surface and ∗ Corresponding author. Tel.: +81 3 5286 3114. E-mail address: ysekine@waseda.jp (Y. Sekine). 0009-2509/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2007.12.017 discharge remain unclear. We investigated the use of surface- and lattice-oxygen of oxide by induction of electric discharge for oxidation of methane in order to clarify the effect of ox- ide catalysts in electric discharge. To elucidate the reaction scheme, we also measured emission spectra induced by elec- tric discharge for observation of activated species on the oxide surface. 2. Experiments Fig. 1 shows a quartz tube used in all experiments as a flow- type reactor. Two stainless steel rods, used as electrodes, were inserted from each end of the quartz tube. Then 400 mg of ox- ide was charged in the middle of the reactor. As oxide samples, MgO (Ube Material Industries Ltd.), TiO 2 (anatase and rutile; Ishihara Sangyo Kaisha Ltd.), ZrO 2 (amorphous, tetragonal and monoclinic; Daiichi Kigenso Kagaku Kogyo Co. Ltd.),