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

Journal Article · Sat Feb 01 04:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90250-L· OSTI ID:7160306

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)

The activation of crystalline and amorphous chromia surfaces by thermal pretreatment in argon and oxygen adsorption at 473 K has been studied by diffuse reflectance FTIR and Raman spectroscopy. The formation of coordinatively unsaturated chromium sites during thermal activation is monitored by observing the evolution of Cr{double bond}O stretching absorptions both in the fundamental and overtone regions of the FTIR spectrum. On {alpha}-Cr{sub 2}O{sub 3}, labile surface oxygen species are largely removed at 498 K, whereas on the amorphous chromia surface, labile oxygen is more tightly bound. As a consequence, coordinatively unsaturated chromium sites are generated on amorphous chromia to a lesser extent than on {alpha}-Cr{sub 2}O{sub 3}. Upon high-temperature oxygen treatment, O{sub 2} is dissociatively adsorbed. Coordinatively unsaturated sites are occupied by the added oxygen, as manifested by an increase in the number of Cr{double bond}O oscillators. Fine structure in the Cr{double bond}O absorptions of the amorphous chromia is observed for the first time, and is tentatively assigned to various types of surface sites. Raman spectroscopic characterization of the amorphous chromia surface reveals laser-induced dehydration and creation of coordinatively unsaturated surface Cr{double bond}O sites, accompanied by progressive crystallization of the amorphous substrate. Differences between crystalline and amorphous chromia with respect to their SCR activity are correlated with the higher density of labile oxygen species available on the surface of amorphous chromia under SCR reaction conditions (423-473 K).

• OSTI ID: 7160306
• 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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ABSORPTION SPECTROSCOPY
ADSORPTION
AMMONIA
AMORPHOUS STATE
ARGON
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL ACTIVATION
CHEMICAL BONDS
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
COMPARATIVE EVALUATIONS
CRYSTAL STRUCTURE
DENITRIFICATION
ELECTROMAGNETIC RADIATION
ELEMENTS
EVALUATION
FLUIDS
FOURIER TRANSFORMATION
GASES
HEAT TREATMENTS
HYDRIDES
HYDROGEN COMPOUNDS
INFRARED RADIATION
INTEGRAL TRANSFORMATIONS
LASER SPECTROSCOPY
MORPHOLOGY
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN OXIDES
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PH VALUE
RADIATIONS
RAMAN SPECTROSCOPY
RARE GASES
REDUCTION
SELECTIVE CATALYTIC REDUCTION
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
TRANSFORMATIONS
TRANSITION ELEMENT COMPOUNDS