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

Journal Article · Sat Feb 01 00:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90251-C· OSTI ID:7160302

Schraml-Marth, M; Wokaun, A ^[1]; Curry-Hyde, H E; Baiker, A ^[2]

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1. Univ. of Bayreuth (Germany)
2. 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), Vol. 133:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
01 COAL, LIGNITE, AND PEAT
36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHROMIUM OXIDES
MORPHOLOGY
SURFACE PROPERTIES
NITRIC OXIDE
SELECTIVE CATALYTIC REDUCTION
ABSORPTION SPECTROSCOPY
AMMONIA
AMORPHOUS STATE
BROENSTED ACIDS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
DESORPTION
FOURIER TRANSFORMATION
INFRARED RADIATION
LEWIS ACIDS
NITROGEN OXIDES
PH VALUE
REFLECTIVITY
SYNTHESIS
TEMPERATURE CONTROL
CHALCOGENIDES
CHROMIUM COMPOUNDS
CONTROL
DENITRIFICATION
ELECTROMAGNETIC RADIATION
HYDRIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INTEGRAL TRANSFORMATIONS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIATIONS
REDUCTION
SORPTION
SPECTROSCOPY
TRANSFORMATIONS
TRANSITION ELEMENT COMPOUNDS
540120* - Environment
Atmospheric- Chemicals Monitoring & Transport- (1990-)
010800 - Coal
Lignite
& Peat- Waste Management
360602 - Other Materials- Structure & Phase Studies
400201 - Chemical & Physicochemical Properties