Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites
- Univ. of Bayreuth (Germany)
- Swiss Federal Inst. of Tech., Zuerich (Switzerland)
Two types of NH{sub 3} molecules bound to Broensted acidic sites on the surface of the chromia catalysts, as well as two species bound to Lewis sites, are identified from the IR spectra. The oxidized surface of {alpha}-Cr{sub 2}O{sub 3} is characterized by a high surface coverage of strongly Lewis-bound ammonia molecules, which desorb at temperatures above 400 K. In contrast, weakly bound NH{sub 3} prevails on the oxidized surface of amorphous chromia. The desorption of the latter species starts at 380 K and is completed around 480 K. A reductive pretreatment of the chromia surfaces by hydrogen (10% in Ar) decreases the number of surface hydroxyl groups and devoids the surface of adsorbed oxygen., As a consequence, the number of Broensted acidic sites is reduced both on the crystalline and the amorphous catalyst. On the reduced surface of {alpha}-Cr{sub 2}O{sub 3}, strongly bound ammonia coordinated to Lewis acidic sites is observed to persist to temperatures beyond 560 K. In contrast, weakly Lewis-bound NH{sub 3} prevails on reduced amorphous chromia, which is quantitatively desorbed at temperatures below 410 K. The formation of NH{sub 3} oxidation products on {alpha}-Cr{sub 2}O{sub 3} is manifested by the observation of two characteristic surface species, an N{sub 2}O{sub 2} dimer and an NO{sub 2} chelate surface complex. Corresponding signals are not observed on the surface of amorphous chromia.
- OSTI ID:
- 7160302
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:2; ISSN 0021-9517; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide
Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 2. Diffuse reflectance FTIR study of thermal treatment and oxygen adsorption
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ABSORPTION SPECTROSCOPY
AMMONIA
AMORPHOUS STATE
BROENSTED ACIDS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
CONTROL
CRYSTAL STRUCTURE
DENITRIFICATION
DESORPTION
ELECTROMAGNETIC RADIATION
FOURIER TRANSFORMATION
HYDRIDES
HYDROGEN COMPOUNDS
INFRARED RADIATION
INORGANIC ACIDS
INTEGRAL TRANSFORMATIONS
LEWIS ACIDS
MORPHOLOGY
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN OXIDES
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PH VALUE
PHYSICAL PROPERTIES
RADIATIONS
REDUCTION
REFLECTIVITY
SELECTIVE CATALYTIC REDUCTION
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
SYNTHESIS
TEMPERATURE CONTROL
TRANSFORMATIONS
TRANSITION ELEMENT COMPOUNDS