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2007_6_Nr6_EEMJ

Chirila et al

Chirila et al /Environmental Engineering and Management Journal 6 (2007), 6, 549-553 Conversia NO x [%] 100 90 80 70 60 50 40 30 20 10 0 600 °C 800 °C 1000 °C 150 200 250 300 350 400 450 500 550 600 650 Oxygen lack in synthetic gas mixture leaded to important changes of conversion curves for both propane oxidation and nitrogen oxides reduction. Fig.6 displays, reduction reaction was favored, while oxidation reaction has kept constant values in whole temperature range in which tests were performed. The higher values for oxidation reaction belong to perovskite sample calcined at 600 o C which proves to be again the most efficient perovskite in propane oxidation while LaMnO 3 sample calcined at 800°C presented lower values, almost negligible. Temperatura [°C] 100 100 90 90 80 Conversia C 3 H 6 [%] 80 70 60 50 40 30 20 10 0 600 800 1000 150 200 250 300 350 400 450 500 550 600 650 Temperatura [°C] Conversiea NO x [%] 70 60 50 40 30 20 10 0 600 800 1000 150 200 250 300 350 400 450 Temperature [°C] Fig. 4. Nitrogen oxides (a) and propene (b) conversion for the LaMnO 3 perovskite samples (propene 600 ppm, NOx 600 ppm) Conversia NO x [%] Conversia C 6 H 8 [%] 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 600 °C 800 °C 1000 °C 150 200 250 300 350 400 450 Temperatura [°C] 600 °C 800 °C 1000 °C 150 200 250 300 350 400 450 Temperatura [°C] Fig. 5. Nitrogen oxides (a) and propane (b) conversion for the LaMnO 3 perovskite samples (propane 400 ppm, NOx 600 ppm, 5% O 2 ) Conversia C 6 H 8 [%] 100 90 80 70 60 50 40 30 20 10 0 600 °C 800 °C 1000 °C 150 200 250 300 350 400 450 Temperatura [°C] Fig. 6. Nitrogen oxides (a) and propane (b) conversion for the LaMnO 3 perovskite samples (propane 400 ppm, NOx 600 ppm) 4. Conclusions The characterization by presented physicochemical methods confirmed that the synthesized samples are perovskite structures with a high homogeneity and crystallinity. The calcination process has leaded to three different symmetry of LaMnO 3 perovskite due to octahedral distortion. It is well known that perovskites present a certain small surface comparing with other catalysts. The BET specific surface of LaMnO 3 perovskite was found 24m 2 /g corresponding to the sample obtained at 600 o C and decreases once with the calcinations temperature rising up to 2.5m 2 /g in the case of calcinations sample at 800 o C. The oxidation state of the manganese from the LaMnO 3 perovskite leaded to 552

Syntheis, characterization and catalytic reduction of NOx emissions over LaMnO 3 perovskite a reducing character just like the reduction analysis at programmed temperature showed. The catalytic activity tests made on the three LaMnO 3 perovskite samples using propena and propan as reduction agent, showed a good oxidation catalytic activity in a rich oxygen medium. For lack of oxygen from the synthetic mixture of gas using propane, the LaMnO 3 perovskite presents activity both in nitrogen oxides reduction and the propane oxidation. In the case of propane the oxidation activity takes place only in the presence of oxygen, while the reduction activity needs a poor oxygen medium and over 400 o C temperatures. For the temperature interval of 150 o -450 o C used in catalytic activity tests the “full” structure type LaMnO 3 had the best activity. A good activity was obtained also in the case of the other two types of structures: La 0.98 MnO 3 and LaMnO 3.15 . Using propene as a reduction agent leads to better results than using propane. The synthesized sample at 800 o C revealed the lowest activity in nitrogen oxides reduction with propene in lack of oxygen References Hackenberger M., (1998), Untersuchungen an Perowskit – Katalysatoren und Perowskit-Traegerkatalyzatoren fuer die Totaloxidation von Schadstoffen, Dissertation, Universität Leipzig, Germany. Alifanti M., Kirchnerova J., Delmon B., (2003), Effect of substitution by cerium on the activity of LaMnO 3 perovskite in methane combustion, Appl. Cat. A: Gen., 245, 231-244. Buciuman F. C., Patcas F., Zsakó J., (2000), TPR-study of Substitution Effects on Reducibility and Oxidative Non-stoichiometry of La0.8A'0.2MnO3+δ Perovskites, Journal of Thermal Analysis and Calorimetry, 61, 819-825. Buciuman F. C., Joubert E., Menezo J. C., Barbier J., (2001), Catalytic properties of La 0.8 A 0.2 MnO 3 (A = Sr, Ba, K, Cs) and LaMn 0.8 B 0.2 O 3 (B = Ni, Zn, Cu) perovskites: 2. Reduction of nitrogen oxides in the presence of oxygen, Appl. Cat. B: Env., 35, 149-156. Kakihana M., Arima M., Yoshimura M., Ikeda N., Sugitani Y., (1999), Synthesis of high surface area LaMnO 3+d by a polymerizable complex method, J. Alloys. Compd. 283, 102-105; Haj K. O., Ziyade S., Ziyad M., Garin F., (2002), DeNO x reaction studies: Reactivity of carbonyl or nitrocompounds compared to C 3 H 6 : influence of adsorbed species in N 2 and N 2 O formation, Appl. Catal. B: Env., 37, 49-62. Liu Y., Zheng H., Liu J., Zhang T., (2002), Preparation of high surface area La 1−x A x MnO 3 (A=Ba, Sr or Ca) ultra-fine particles used for CH 4 oxidation, Chem. Eng. J., 89, 213-221. Ng Lee Y., Lago R. M., Fierro J. L. G., Cortés V., Sapiña F., Martínez E., (2001), Surface properties and catalytic performance for ethane combustion of La 1−x K x MnO 3+δ perovskites, Appl. Cat. A: Gen., 207, 17-24. Patcas F., Buciuman F. C., Zsako J., (2000), Oxygen nonstoichiometry and reducibility of B-site substituted lanthanum manganites, Termochim. Acta, 360, 71-76. Rottländer C., Andorf R., Plog C., Krutzsch B., Baerns M., (1996), Selective NO reduction by propane and propene over a Pt/ZSM-5 catalyst: a transient study of the reaction mechanism, Appl. Cat. B: Env., 11, 49- 63. Spinicci R., Faticanti M., Marini P., De Rossi S., Porta P., (2003), Catalytic activity of LaMnO 3 and LaCoO 3 perovskites towards VOCs combustion, J. Mol. Cat. A: Chem., 197, 147-155. Spinicci R., Delmastro A., Ronchetti S., Tofanari A., (2002), Mater. Chem. Phys., 78, 393-399; Stephan K., Hackenberger M., Kießling D., Wendt G., (2004), Total oxidation of methane and chlorinated hydrocarbons on zirconia supported A1-xSrxMnO3 catalysts, Chem. Eng. Technology, 27, 687-693. Teraoka Y., Harada T., Kagawa S., (1998), Reaction mechanism of direct decomposition of nitric oxide over Co- and Mn-based perovskite-type oxides, J. Chem. Soc., Faraday Trans., 94, 1887-1891. Tran D. N., Aardahl C. L., Rappe K. G., Park P. W., Boyer C. L., (2004), Reduction of NO x by plasma-facilitated catalysis over In-doped γ-alumina, Appl. Cat. B: Env., 48, 155-164. 553

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