TPD Study of Mordenite-Type Zeolites for Selective Catalytic Reduction of NO by NH 3
ABSTRACT The effect of the adsorption of NO and NH3on catalytic activity has been examined by temperature-programmed desorption over a series of cation-exchanged mordenite catalysts for selective catalytic reduction (SCR) of NO by NH3. The catalytic activity observed in a packed-bed flow reactor was well correlated with the cation content of the catalyst and its adsorption properties, making it possible to elucidate the role of metals and acidity in this reaction system. The amount of NH3and NO adsorbed on the catalyst surface proportionally increased with the degree of cation exchange of the catalyst, especially at the Brønsted acid site (H+) and the metal site (Cu2+). SCR activity also gradually increased with the acidity of the catalyst and/or its degree of catalyst cation exchange. Surface acidity of the mordenite catalysts appears to be a dominant factor in the high performance of the SCR reaction system. The common activation energy is observed to be about 12 kcal/mole for NaHM and CuHM catalysts, independent of their cation content on the catalyst surface. The active sties of this catalytic system are both the Brønsted acid site and the metal site. Furthermore, the reaction occurred in a Langmuir–Hinshewood manner with a dual-site catalysis mechanism.
- SourceAvailable from: Rajamani GounderJournal of Catalysis 04/2014; 312:26–36. · 5.79 Impact Factor
- Journal of Chemical Engineering of Japan - J CHEM ENG JPN. 01/2001; 34(2):148-153.
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ABSTRACT: The catalytic activity of sulfated titania (ST) calcined at a variety of temperatures has been investigated for selective catalytic reduction (SCR) of NO by NH3. The NO removal activity of ST catalyst mainly depends on its sulfur content, indicating critical role of sulfur species on the surface of TiO2. The role of sulfur is mainly the formation of acid sites on the catalyst surface. The presence of both Br�nsted and Lewis acid sites on the surface of sulfated titania has been identified by IR study with the adsorption of NH3 and pyridine on ST. The reduction of the intensity of IR bands representing Br�sted acid sites is more pronounced than that revealing Lewis acid sites as the calcination temperature increases. It has been further clarified by IR study of ST500 catalyst evacuated at a variety of temperatures. The NO removal activity also decreases with the increase of the catalyst calcination temperature. It simply reveals that Br�nsted acid sites induced by sulfate on the catalyst surface are primarily responsible for the enhancement of catalytic activity of ST catalyst containing sulfur for NO reduction by NH3.Korean Journal of Chemical Engineering 01/2003; 20(2):273-278. · 1.06 Impact Factor