Plasma-assisted oxidation of carbon particle by lattice oxygen on/in oxide catalyst Yasushi Sekine a,b,⇑ , Hiroshi Koyama a , Masahiko Matsukata a , Eiichi Kikuchi a a 65-301, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan b CREST, Tokyo, Japan article info Article history: Received 26 November 2010 Received in revised form 21 March 2011 Accepted 22 March 2011 Available online 11 April 2011 Keywords: Lattice oxygen Carbon particle Plasma-assisted oxidation Fluidized bed DBD plasma abstract Oxidation of carbon particles by lattice oxygen on/in catalysts was investigated with and without electri- cal discharge at 673 K in a fluidized bed reactor. Application of dielectric barrier discharge promoted the evolution of lattice oxygen in the oxide catalyst, and oxidation of carbon by the evolved lattice oxygen was accelerated by application of the discharge. The total amount of consumed lattice oxygen in/on the catalyst was not changed by the application of the discharge due to the low diffusion rate of bulk oxy- gen at low temperature. Metal-loaded catalysts such as Ni/CeO 2 evolved larger amounts of lattice oxygen because of interaction between the supported Ni particle and ceria support. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Solid carbon particles such as char, soot, and coke derived from combustion and gasification of diesel fuel, heavy oil, coal and bio- mass have low reactivity compared to that of gaseous/liquid prod- ucts. Especially, solid carbon exhausted from a diesel engine, called particulate matter (PM), brings on air pollution and is known as a hazardous material to the human body [1–4]. In addition, char and coke produced by gasification or combustion of coal [5–9] or biomass [10–16] are known to have low reactivity. Oxidative re- moval of these solid carbon species by gas-phase oxygen in air re- quires high temperatures because of its high activation energy. Recently, many investigations have been made into catalytic oxida- tion of these carbon species at lower temperature with solid oxides such as CeO 2 . These processes include redox processes; that is to say, solid carbon species are oxidized by active lattice oxygen in oxi- des such as CeO 2 , and consumed lattice oxygen is regenerated by gaseous oxygen in air. Some modified CeO 2 oxides with rare-earth metal catalyzes low-temperature oxidation of solid carbon because of its effect of promoting evolution of lattice oxygen [17–20]. In addition, metal oxides having a low melting point such as alkaline metals and alkaline earth metals show high reactivity because these metal oxides easily melt on carbon at the reaction temperature. The melt phase brings increased contact interfaces between catalyst and carbon particles. For the oxidation of solid carbon with oxide cata- lysts, the contact state between catalyst and carbon is very impor- tant. Especially for oxidation of PM or soot, some reports have described that the contact state of catalyst and carbon, whether soft-contact or tight-contact determined the oxidation rate of car- bon species [21,22]. In this work, we examined the oxidation of solid carbon particle by solid oxides in a fluidized bed reactor to maintain stable contact between the catalyst and carbon particles. Furthermore, these solid oxide catalysts evolve lattice oxygen to oxidize carbon particles, but the evolution rate of oxygen is the rate-determining step, especially at lower temperatures such as 673 K. Some researchers investigated the application of plasma to accelerate the oxidation of carbon species [23–27]. We also previ- ously studied oxidation of methane over solid oxide catalysts with electric discharge. The electric discharge promoted the release of lattice oxygen in/on catalysts to increase the oxidation activity [28]. Therefore, we conducted all experiments of oxidation of carbon with oxide catalysts in a fluidized bed to determine the ‘‘real’’ reac- tion rate with an application of electrical discharge (dielectric bar- rier discharge). In this study, we investigated the oxidation rate of carbon by oxide catalyst. The regeneration of lattice oxygen in the oxide was not evaluated. 2. Experimental 2.1. Catalysts Regarding the catalysts, we prepared various Ce-containing oxides—CeO 2 , CePrO x , BaCeMnO x , Pt/BaCeMnO x . In addition, for CeO 2 oxide, we prepared two samples: CeO 2 -1 (JRC-CEO-1; sup- plied by the Catalysis Society of Japan) and CeO 2 -2 (Kanto Chem- ical Co. Inc.). To investigate the effect of supported metal, we also prepared some metal-supported ceria catalysts: X/CeO 2 -1 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.03.046 ⇑ Corresponding author at: CREST, Tokyo, Japan. E-mail address: ysekine@waseda.jp (Y. Sekine). Fuel 103 (2013) 2–6 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel