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https://hdl.handle.net/20.500.14279/11046
Τίτλος: | Understanding the synergistic catalytic effect between la2O 3 and CaO for the CH4 Lean De-NOx reaction: Kinetic and mechanistic studies | Συγγραφείς: | Anastasiadou, T. Loukatzikou, Loukia A. Costa, Costas |
Major Field of Science: | Natural Sciences | Field Category: | Chemical Sciences | Λέξεις-κλειδιά: | Calcium compounds;Chemisorption;Cyanides;Doping (additives);Lanthanum compounds;Photoluminescence;Reaction kinetics | Ημερομηνία Έκδοσης: | 28-Ιου-2005 | Πηγή: | Journal of Physical Chemistry B, 2005, Volume 109, Issue 28, Pages 13693-13703 | Περίληψη: | Doping of La2O3 crystallites with Ca2+ ions significantly enhances the intrinsic rate of NO reduction by CH4 in the presence of 5% O2 at 550°C compared to pure La 2O3 and CaO solids, while the opposite is true after doping of CaO with La3+ ions. It was found that the 5 wt % La 2O3-95 wt % CaO system has one of the highest intrinsic site reactivities (TOF = 8.5 × 10-3 s-1) reported at 550°C for the NO/CH4/O2 reaction among metal oxide surfaces. The doping process occurred after first dispersing La 2O3 and CaO crystallites in deionized water heated to 60°C for 90 min, while the dried material was then ground and heated slowly in air to 800°C and kept at this temperature for 5 h. The doping process had the effect of creating surface oxygen vacant sites (F-type defects) in the oxide lattices the concentration of which is a function of the wt % La 2O3 used in the mixed oxide system as revealed by photoluminescence and O2 chemisorption studies. According to DRIFTS 15NO transient isotopic experiments (SSITKA), oxygen vacant sites in Ca2+-doped La2O3 promote the formation of a more active chemisorbed NOx species (NO2 -) that contributes to the enhancement of reaction rate as compared to pure lanthana, calcium oxide, and La3+-doped CaO. These results were supported by the kinetic orders of the reaction with respect to NO and O2 obtained as a function of wt % La2O3 content in the mixed oxide system. Carbon dioxide (a reaction product) competes for the same oxygen vacant sites to form stable adsorbed carbonate-like species, thus lowering the reduction rate of NO. The dependence of the reaction TOF on the wt % La 2O3 loading at 550°C was found to follow the trend of the dependence of photoluminescence intensity on the wt % La2O 3 content in the La2O3-CaO oxide system. | URI: | https://hdl.handle.net/20.500.14279/11046 | ISSN: | 15206106 | DOI: | 10.1021/jp0515582 | Rights: | © 2005 American Chemical Society. | Type: | Article | Affiliation: | University of Cyprus University of Ioannina |
Publication Type: | Peer Reviewed |
Εμφανίζεται στις συλλογές: | Άρθρα/Articles |
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