Chromia on titania. IV. Nature of active sites for selective catalytic reduction of NO by NH[sub 3]

Journal Article · Fri Apr 01 04:00:00 EST 1994 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1994.1093· OSTI ID:7185278

Schneider, H; Baiker, A ^[1]; Scharf, U; Wokaun, A ^[2]

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1. Swiss Federal Institute of Technology, Zurich (Switzerland)
2. Univ. of Bayreuth (Germany)

The surface sites on titania-supported chromia (CrO[sub x]/TiO[sub 2]), which are relevant for the selective catalytic reduction (SCR) of NO by NH[sub 3], and the undesired formation of N[sub 2]O have been investigated using temperature-programmed desorption (TPD) combined with in situ diffuse reflectance FTIR spectroscopy (DRIFT). The combined TPD and DRIFT measurements carried out on the differently pretreated (reduced, oxidized, exposed to SCR conditions) CrO[sub x]/TiO[sub 2] indicate that Broensted-bound ammonia is crucial for the SCR reaction. N[sub 2]O is formed at temperatures above 450 K by direct oxidation of Lewis-bound NH[sub 3] with oxygen present in the SCR feed gas. TPD measurements carried out with CrO[sub x]/TiO[sub 2] previously loaded with NO and NH[sub 3], respectively, showed that neither oxidized nor reduced CrO[sub x]/TiO[sub 2] covert NO in the absence of NH[sub 3] at the temperature used for SCR. TPD experiments with CrO[sub x]/TiO[sub 2], previously either reduced or oxidized and then exposed to the SCR feed gas, showed that the surface reduced with ammonia is inactive for the desired selective reaction between NO and NH[sub 3], indicating that a partially oxidized state of the surface must be maintained for SCR; this observation confirms the crucial role on the oxygen in the SCR feed gas. The studies indicate that Broensted-bound ammonia, characterized by bands at 1662 and 1425 cm[sup [minus]1], enhances the adsorption of NO and is involved in the selective catalytic reduction of NO to N[sub 2]. 27 refs., 10 figs.

• OSTI ID: 7185278
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 146:2; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
330701 -- Emission Control-- Nitrogen Oxides
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
REDUCTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS