Ag/ALUMİNA KATALİZÖRLERİ ÜZERİNDE ÜRENİN BOZUNMASININ İNCELENMESİ

Dizel araçlardan çevreye salınan zararlı NOx gazları, seçici katalitik indirgeme (SCR) reaksiyonları ile N2 gazına dönüştürülebilmektedir. Bu reaksiyonların verimi, kullanılan indirgen maddeye önemli ölçüde bağlıdır. Ürenin hem kendisi hem de bozunma/hidroliz bileşikleri olan izosiyanik asit (HNCO) ve amonyak (NH3) SCR reaksiyonlarında kullanılabilmektedir. Bundan dolayı, üre son zamanlarda ilgi çeken bir indirgen maddedir. NOx indirgenmesinde Ag/Al2O3 katalizörleri önemli bir yere sahiptir. Sol-jel yöntemi kullanılarak hazırlanan %1 Ag/Al2O3 ve %2 Ag/Al2O3 katalizörü üzerinde ürenin bozunma ve hidroliz bileşikleri FTIR cihazı kullanılarak incelenmiştir. Deneysel çalışmalar, helyum ortamında 100 400°C sıcaklık aralığında gerçekleştirilmiştir. FTIR spektrumlarının analizi sonucunda katalizörler üzerinde ürenin bozunma ve hidroliz bileşikleri olarak NH3, NH4 + , -CNO, melamin ve CO2 tespit edilmiştir. Bunun yanı sıra OH, CH, NH ve C=O gerilme titreşim bantları da gözlenmiştir. NH4 +bileşiği %2 Ag/Al2O3 katalizörü üzerinde 100 ve 250 °C sıcaklıklarda gözlenirken, %1 Ag/Al2O3 katalizörü üzerinde hiçbir sıcaklıkta tespit edilmemiştir. Ürenin bozunma ve hidroliz bileşiği olan amonyak her iki katalizör üzerinde de çalışılan bütün sıcaklık ve zamanlarda gözlenmiştir. Ürenin bozunma bileşiği olan izosiyanat (-CNO), %1 Ag/Al2O3 katalizörü üzerinde en şiddetli pikini 200°C sıcaklıkta, %2 Ag/Al2O3 katalizörü üzerinde 250°C sıcaklıkta vermiştir.

THE INVESTIGATION OF UREA DECOMPOSITION OVER Ag/ALUMINA CATALYSTS

The NOx gases which are released from diesel vehicles can be reduced to N2 gas with selective catalytic reduction (SCR) reactions. The yield of these reactions are majorly related to the reducing agent. Both urea and its decomposition/hydrolysis compounds which are isocyanic asid (HNCO) and ammonia (NH3) can be used SCR reactions. Therefore, urea is an attractive reducing agent recently. Ag/Al2O3 catalysts have an important role for NOx reduction. The decomposion and hydrolysis compounds of urea on the %1 Ag/Al2O3 and %2 Ag/Al2O3 catalysts which are prepared by sol-gel method were investigated by using FTIR. The experimental studies were carried out between 100-400°C temperature in the presence of helium. As a result of the analyses of FTIR spectra, NH3, NH4 + , -CNO, melamine and CO2 were dedected as the decomposition and hydrolysis compounds of urea on the catalysts. Besides that, OH, CH, NH and C=O stretching vibration bands were also observed. NH4 + compound was not observed at any temperature on the %1 Ag/Al2O3 catalyst however, it was observed at the temperatures of 100 and 250 °C on the %2 Ag/Al2O3 catalyst. Ammonia, which is a decompositon and hydrolysis compound of urea, was observed on both catalysts at all temperatures and times. Isocyanate (-CNO), which is a decompositon compound of urea, gave its most intensive peak at the temperature of 200°C on %1 Ag/Al2O3 catalyst and at the temperature of 250°C on %2 Ag/Al2O3 catalyst.

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1. Miyadera, T., Alumina-Supported Silver Catalysts for the Selective Reduction of Nitric Oxide with Propene and Oxygen-Containing Organic Compounds, Applied Catalysis B: Environmental, Cilt 2, No 2-3, 199-205, (993.
2. Bethke, K.A., and Kung, H. H.Supported Ag Catalysts for the Lean Reduction of NO with C3H6, Journal of Catalysis, Cilt 72, 93-102, 1997.
3. Ueda, A., Oshima, T., and Haruta, M., Reduction of Nitrogen Monoxide with Propene in the Presence of Oxygen and Moisture over Gold Supported on Metal Oxides, Applied Catalysis B: Environmental , Cilt12, No 2-3, 81-93, 1997.
4. Kramlich, J.C and Linak, W.P. Nitrous Oxide Behavior in the Atmosphere, and in Combustion and Industrial Systems, Progress in Energy and Combustion Science, Cilt 20, No 2, 149 202, 1994.
5. Van Kooten, W.E.J, Krijnsen, H.C, Van Den Bleek, C.M, Calis, H.P.A, Deactivation of Zeolite Catalysts Used for NOx Removal, Applied Catalysis B: Environmental, Cilt 25, No 23, 125135, 2000.
6. Long, R.Q., Yang, R.T, Characterization of FeZSM5 Catalyst for Selective Catalytic Reduction Nitric Oxide by Ammonia, Journal of Catalysis, Cilt 194, 80-90, 2000.
7. Richter, M., Trunschke, A., Bentrup, U., Brzezinka, K., Schreier, E., Schneider M. , Pohl, M. , Fricke, R. Selective Catalytic Reduction of NO by Ammonia over Egg-shell MnOx/NaY Composite Catalysts, Journal of Catalysis, Cilt 206, 98-113, 2002.
8. Seker, E. , Yasyerli, N. , Gulari, E. , Lambert, C. , Hammerle, R.H , NO Reduction by Urea under Lean Conditions over Single Sol-Gel Cu/Alumina Catalyst , Journal of Catalysis, Cilt 208, 1520, 2002.
9. He, H., Li, Y., Zhang, X., Yu, Y., Zhang, C., Precipitable Silver Compound Catalysts for Selective Catalytic Reduction of NOx by Ethanol, Applied Catalysis A: General, Cilt 375, 258-264,2010.
10. Dong, H., Shuai, S., Li, R., Wang, J., Shi, X., He, H., Study of NOx Selective Catalytic Reduction by Ethanol over Ag/Al2O3 Catalyst on a HD Diesel Engine, Chemical Engineering Journal, Cilt 135, 195-201,2008.
11. Breen, J.P., Burch, R., Hill, C.J., NOx Storage During H2 Assisted Selective Catalytic Reduction of NOx Reaction over a Ag/Al2O3 Catalyst, Catalysis Today, Cilt 145, 34-37, 2009.
12. Shimizu, K., Satsuma, A., Hydrogen Assisted Urea-SCR and NH3-SCR with Silver-Alumina as Highly Active and SO2- Tolerant De-NOx Catalysis, Applied Catalysis B: Environmental, Cilt77, 202-205, 2007.
13. Richter, M., Bentrup, U., Eckelt, R., Schneider M. , Pohl, M.M. , Fricke, R., The Effect of Hydrogen on the Selective Catalytic Reduction of NO in Excess Oxygen over Ag/Al2O3, Applied Catalysis B: Environmental, Cilt 51, 261-274, 2004.
14. Seker, E., Cavataio, J., Gulari, E., Lorpongpaiboon, P., Osuwan, S., Nitric Oxide Reduction by Propene over Silver/Alumina and Silver-Gold/Alumina Catalysts: Effect of Preparation Methods, Applied Catalysis A: General, Cilt 183, 121-134, 1999.
15. Zhang, C., He, H., Shuai, S., Wang, J., Catalytic Performance of Ag/Al2O3-C2H5OH-Cu/Al2O3 System for the Removal of NOx from Diesel Engine Exhaust, Environmental Pollution, Cilt 147, 415-421, 2007.
16. Liu, Z., Li, J., Hao, J., Selective Catalytic Reduction of NOx with Propene over SnO2/Al2O3 Catalyst, Chemical Engineering Journal, Cilt 165, No 1, 420-425, 2010.
17. Eichelbaum, M., Farrauto, R. J., Castaldi, M.J., The Impact of Urea on the Performance of Metal Exchanged Zeolite for the Selective Catalytic Reduction of NOx Part I. Pyrolysis and Hydrolysis of Urea over Zeolite Catalysts, Applied Catalysis B: Environmental, Cilt 97, No 1, 90-97, 2010.
18. Lundström, A., Snelling, T., Morsing, P., Gabrielson, P., Senar, E., Olsson, L., Urea Decomposition and HNCO Hydrolysis Studied over Titanium Oxide, Fe-Beta and γ-Alumina, Applied Catalysis B: Environmental, Cilt 106, 273-279, 2011.
19. Bernhard, A.M., Peitz, D., Elsener, M., Wokaun, A., Kröcher, O., Hydrolysis and Thermolysis of Urea and Its Decomposition Byproducts Biuret, Cyanuric Acid and Melamine over Anatase TiO2, Applied Catalysis B: Environmental, Cilt 115-116, 129-137, 2012.
20. Şahin, A., Aktan, H., Balbaşı, M., Ar, İ., Synthesis and Characterization of Phosphonated Poly(Vinyl Alcohol) Based Membrane with Silica Support , J. Fac. Eng. Archit. Gazi Univ., Cilt 25, No 4, 693-699, 2010.
21. Şahin, A., Balbaşı, M., Ar, İ., Synthesis and Characterization of Sulphonated Polystyrene/Polyvinyl Alcohol Composite Membrane with Boric Acid and Boron Phosphate Support , J. Fac. Eng. Archit. Gazi Univ., Cilt 24, No 1, 137-144, 2009.
22. Yaşyerli, S., Aktaş, Ö., MCF Supported V-MoNb Catalysts Prepared by Dırect Hydrothermal Synthesıs and Impregnatıon Methods for Oxıdatıve Dehydrogenatıon of Propane, J. Fac. Eng. Archit. Gazi Univ., Cilt 27, No 1, 49-58, 2012.
23. Yasyerli, N., Tasdemir, M., FTIR Studies of Urea Decomposition over Pt-Alumina and CuAlumina Catalysts, International Journal of Chemical Reactor Engineering, Cilt 8, No 1, A162, 2010.
24. Park, P.W., Boyer, C.L, Effect of SO2 on the Activity of Ag/γ-Al2O3 Catalysts for NOx Reduction in Lean Conditions, Applied Catalysis B: Environmental, Cilt 59, No 1-2, 27-34, 2005.
25. Lowell, S., Shield,J. Powder Surface Area and Porosity, Chapman and Hall, New York, A.B.D, 1984.
26. Sing, K.S.W, Haul, R.A.W, Pierotti, R.A., Siemieniewska, T., Reporting Physisorption Data for Gas/Solid Systems with Special Reference to the Determination of Surface Area and Porosity, Pure & App. Chem., Cilt 57, No 4, 603-619, 1985.
27. Chen, L.F., Gonzalez, G., Wang, J.A, Norena, L.E., Toledo, A., Castillo, S., Pineda, M.M., Surfactant Control Synthesis of Pd/Ce0.6Zr0.4O2 Catalyst for NO Reduction by CO with Excess Oxygen, Applied Surface Science, Cilt 243, 319-328, 2005.
28. Li, Q., Zhao, N., Wei, W., Sun, Y., Catalytic Performance of Metal Oxide for the Synthesis of Propylene Carbonate from Urea and 1,2 Propanediol, Journal of Moleculer Catalysis A: Chemical, Cilt 270, No 1-2, 44-49, 2007.
29. Li, G., Jones, C.A, Grassian, V.H, Larsen, S.C., Selective Catalytic Reduction of NO2 with Urea in Nanocrystalline NaY Zeolite, Journal of Catalysis, Cilt 234, No 2, 401-413, 2005
30. Seker, E. , Yasyerli, N. , Gulari, E. , Lambert, C. , Hammerle, R.H , NOx Reduction by Urea under Lean Conditions over Single Sol-Gel Pt/Alumina Catalyst , Applied Catalysis B: Environmental, Cilt 37, No 1, 2735, 2002.