Catalytic Oxidation of Nitric Oxide to Nitrogen Dioxide on Ru-FAU
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Catalytic Oxidation of Nitric Oxide to Nitrogen Dioxide on Ru-FAU Lingling Qu Æ Jinjun Li Æ Zhengping Hao Æ Landong Li
Received: 13 March 2009 / Accepted: 27 March 2009 / Published online: 27 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Ru-FAU samples were prepared by wet impregnation and studied as promising catalysts for NO oxidation. The existence of rare earth ions in FAU structure showed positive effect on NO oxidation while the existence of alkali metal ions on cation sites showed negative effect. As a result, Ru-REY exhibited the best activity and a maximal NO conversion of ca. 94% was obtained at 250 °C at a very high WHSV of 180,000 h-1. Keywords REY
NO oxidation Ru catalysts FAU zeolite
1 Introduction Nitrogen oxides are known to be associated with several environmental and health hazards, including photochemical smog and acid rain. Due to the increasingly stringent regulations on nitrogen oxide emissions, various posttreatment methods have been attempted for the reduction of NOx emissions in excess oxygen [1]. In the case of stationary sources, the selective catalytic reduction of NOx by ammonia (NH3-SCR), a state-of-the-art technology for NOx abatement, has been extensively studied. In the case of mobile sources, the selective catalytic reduction of NOx by hydrocarbons (HC-SCR) and NOx storage and reduction L. Qu J. Li Z. Hao L. Li (&) Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085 Beijing, People’s Republic of China e-mail: [email protected] L. Qu China University of Mining & Technology (Beijing), 100083 Beijing, People’s Republic of China
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(NSR) are two major techniques and draw much attention. During the above-mentioned processes, it becomes more and more evident now that NO2 plays a decisive role. For NOx storage and reduction, NO is first oxidized to NO2 over the noble metal component and then stored as nitrates or nitrites on the basic component [2]. For the selective catalytic reduction of NOx, NO is partially oxidized to NO2, which subsequently reacts with hydrocarbon or NH3 to give out N2 [3]. More important, the so-called ‘‘fast’’ SCR reaction (4NH3 ? 2NO ? 2NO2 ? 4N2 ? 6H2O), in contrast to standard ammonia SCR reaction (4NH3 ? 4NO ? O2 ? 4N2 ? 6H2O), is drawing more and more attention in recent years [4–8]. The reaction between equimolar NO–NO2 and NH3 is ca. 10 times faster than the reaction between NO and NH3 at low temperatures (200– 300 °C). Therefore, the fast SCR reaction is considered as a feasible means to boosting the denitrification efficiency at lower temperatures as well as to reducing the catalyst costs of SCR system. However, it is known that nitrogen oxides produced from emission sources mainly consist of NO ([90%). Thus, the oxidation of NO to NO2 becomes a key step to realize the fast SCR process and catalysts with sufficient activity for NO oxidation are being researched. During the research of NO oxidation catalysts, supported platinum catalysts drew much attention. Pt/SiO2 [9, 10] and Pt/Al2O3 [1
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