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Current Topics in Catalysis   Volumes    Volume 13 
TPD study of NO adsorption in the presence of O2 over Ag-, Cu- and Fe-containing catalysts: Relationship between SCR activity and acid-base property
Wladimir Suprun, Denis Worch, Krzystof Soja, Michal Pietraszek, Teresa Grzybek
Pages: 67 - 90
Number of pages: 24
Current Topics in Catalysis
Volume 13 

Copyright © 2017 Research Trends. All rights reserved

Cu-, Fe- and Ag-containing catalysts supported on γ-alumina, silica, SAPO-11 and Y-zeolite with 3 wt.% of metal loading were synthesized by the impregnation technique and characterized by N2-adsorption, H2-TPR and by the temperature-programmed desorption (TPD) of ammonia and NO. Additionally the textural properties, acidity and adsorption capacity of parent support materials were determined by above-described methods. The adsorption capacity of NOx (ACNOx) was quantified in the temperature range of 373 K to 823 K in continuous flow of NO + O2 and after saturation with NO at 90 °C in the presence of oxygen excess. It was found that the NOx uptake decreased as the temperature increased with maximum at 373 K. Total uptake of NOx depended on the type of transition metal, the content of Al in the support material, acidic site density and surface area. Two NOx desorption regions were found by TPD experiments over γ-Al2O3 after exposure to either a NO and O2 or NO2-containing gas, i.e., in a temperature range from 420 K to 500 K and from 550 K to 800 K. The latter one corresponds to a desorption of differently bonded NOx species. In-situ diffuse reflectance infrared fourier transform (DRIFT) spectroscopy of γ-alumina, 3Ag/Al2O3, 3FeO/Al2O3 and 3CuO/Al2O3 in the presence of NO and excess O2 shows that NO is mainly adsorbed in the form of nitrates and that it is oxidized to NO2 above 673 K. Catalysts containing Cu and Fe oxides show a higher activity for the oxidation of NO to NO2 than the Ag-containing counterparts. Ag, Cu and Fe oxides supported on silica possess a lower ACNOx in comparison to alumina- and zeolite-supported samples. The determined value of NO adsorption capacity allowed rationalizing some of the earlier results on selective catalytic reduction (SCR) of NOx in the presence of ethanol.
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